A TISSUE CAVITY DISTENDING SYSTEM WITH LOW TURBULENCE
FIELD OF INVENTION
The present invention relates to a system for distendmg body tissue cavities of subjects utilizmg continuous flow imgation durmg endoscopic procedures The system and the methods of the present invention descnbed above can be used in any endoscopic procedure requinng contmuous flow irrigation few examples of such endoscopic procedures bemg hysteroscopic surgery, arthroscopic surgery, trans uretheral surgery (TURP), endoscopic surgery of the bram and endoscopic surgery of the spine The proposed invention can also have certain useful non medical applications.
BACKGROUND OF THE INVENTION
Endoscopic surgery is becoming mcreasingly popular because of the following reasons
(a) it is a minimally invasive form of surgery,
(b) It avoids large incisions over the skin and muscle,
(c) It is associated with less pam,
(d) there is a relatively less requirement of blood transfusions and
(e) the patients can return back to normal work relatively early with minimal loss of working days
While m the correspondmg open conventional surgeries a relatively large body part consisting of skm and muscle needs to be cut in order to gam access to an underlying body tissue cavity, in endoscopic surgery instead of cutting body structures like skin and muscle an endoscope is mtroduced into the body cavity via the natural openmg of a cavity, if such exists, or alternatively a minute hole is made in the wall of the cavity through which the endoscope is introduced to visualize the intenor of the body tissue cavity and to perform major or minor endoscopic surgical procedures For this reason endoscopic surgery is also sometimes called 'key hole' or 'mmimal access surgery' Besides reducmg the pain associated with surgery, endoscopic surgery also helps m reducing the medical expenses ENDOSCOPIC SURGERY is PRIMARILY RELATED TO A TISSUE CAVITY: All endoscopic surgeries are earned out on a existmg body cavity which is distended or 'ballooned up' by a suitable distending apparatus which permits the inner lining of the said tissue cavity to be visualized by the help of an endoscope. Though multiple endoscopic procedures have become established as the preferred surgical modality but still there is immense scope of mcreasmg the safety and efficiency of the such existing endoscopic procedures by improving upon the existing techniques and apparatus used for distending

body tissue cavities Hysteroscopy, arthroscopy, TURP (transuretheral resection of the prostate), endoscopic surgery of the brain and endoscopic surgery of the spine are few of the routmely performed endoscopic procedures and the organs related to such surgenes being uterus, human jomts, bladder, bram and the spine respectively The list of endoscopic surgenes is long, ever increasmg and there is hardly any body organ or organ system to which the benefits of endoscopy have not been extended
TISSUE CAVITIY IS INITIALLY COLLAPSED IN ITS NATURAL STATE: In the natural state tissue cavities are collapsed structures and the cavity walls are in apposition with each other as if kissing each other Thus if an endoscope is introduced in such a collapsed cavity no endoscopic visualization is possible unless the cavity is ballooned up by filling It with a transparent fluid or a gas Such ballooning of a tissue cavity is technically termed as 'cavity distension' No endoscopic procedure can be performed without an efficient cavity distendmg system and no endoscopic procedure should be attempted without a safe distending system because unsafe tissue cavity distendmg means can lead to extreme human morbidity and even the death of a patient and such gnm realities shall be discussed in the later sections of this manuscnpt Cavity distension provides both endoscopic visualization and mechanical distension which is necessary for the movement of endoscopic mstruments CONTINUOUS FLOW IRRIGATION:
In the present invention, the Inventors are focused on a system for distending body tissue cavities for those endoscopic procedures m which the cavity needs to be distended by utilizing continuous flow imgation only Here, the term 'continuous flow irngation' means that fluid simultaneously enters and escapes from a tissue cavity via separate entry and exit points, as a result of which a positive fluid pressure is created inside the tissue cavity which distends the cavity
THE NEED FOR CONTINUOUS FLOW IRRIGATION:
Any tissue cavity can be easily distended in a 'static manner' by simply pushing fluid via a single inflow tube mserted into the cavity and in this manner a desired cavity pressure can be developed and also maintained For example, a cavity can be distended by pressing on the piston of a simple synnge filled wilii fluid witti the outlet end of the synnge being connected to the cavity by a tube Alternatively a fluid filled bottle may be elevated to a suitable height and under the influence of gravity fluid from such bottle may be allowed to enter the cavity via a tube connecting the said bottle to the cavity and m this manner a desired static pressure can be developed and also mamtained Though it is very easy to achieve distension by the said static manner, it is not a practical solution because blood and tissue debns which are
mvanably released from the fragile cavity inner Immg mix with the distendmg fluid and
endoscopic vision gets clouded within a few seconds or a few mmutes Thus continuous flow
irrigation is needed to constantly wash away blood and tissue debns m order to maintain
constant clear endoscopic vision
CAVITY PRESSURE AND CAVITY FLOW RATE:
It is obvious that cavity fluid pressure and the flow rate through the cavity are the two basic
parameters associated with all continuous flow irrigation systems.
AN EFFICIENT DISTENDING SYSTEM:
The Inventors believe that an efficient distending system is the one which provides a
predictably continuous clear visualization and a predictably stable mechanical stabilization of
the cavity walls In order to achieve this the Inventors believe that a suitable stable constant
precise cavity pressure and a suitable stable precise cavity flow rate have to be created and
mamtained m a predictable and controlled manner The cavity pressure should be adequate so
that vision is not clouded by oozing of blood and enough mechanical separation of the cavity
walls occurs to allow the movement of the endoscope Similarly, the cavity flow rate should
be adequate enough to constantly wash away blood and tissue debris m order to allow clear
vision Many pnor systems utilize a penstaltic pump over the inflow and or the outflow side
and these peristaltic pumps create pressure pulsations which are then transmitted to the tissue
cavity Such pressure pulsations are undesirable and the main aim of the present invention is
to dampen such pressure pulsations
A SAFE DISTENDING SYSTEM:
An efficient distending system as explained in the previous paragraph need not also be a safe
distending system In this regard, the Inventors would like to highlight that if the cavity
pressure nses above the prescnbed safe limits excessive fluid intravasation may occur or the
cavity may even burst Fluid intravasation is a process by which the irrigation fluid enters
into the patient's body system through the cavity walls and may cause significant danger to
the patient's life including death Thus a safe distendmg system is one which prevents or
minimizes fluid intravasation and allows the surgeon to accurately know the instantaneous
real time rate of fluid intravasation into the patient's body system
NO PRIOR ART IS ABSOLUTELY SAFE:
Many different types of utenne distending systems are known and are being commercially
marketed by many different companies but none of these systems can be considered to be
absolutely safe for the patient This fact has been clearly stated m the 'Hysteroscopic Fluid
Momtonng Guidelines proposed by the Ad Hoc Committee on Hysteroscopic Fluid
Guidelines of the Amencan Association of Gynecologic Laproscopists February 2000 (Loffler FD, Bradley LD, Bnll AI et al Hysteroscopic fluid monitoring guidelines The journal of the Amencal Association of Gynecologic Laproscopists 7(1) 167-168, 1994) where the authors clearly and explicitly state "fluid pumps for low-viscosity media are a convenience and do not guarantee safety" The present invention aims at providing a distending system which is both safer and more efficient in companson to all the pnor art systems
BASIC PHYSICS OF CAVITY DISTENSION:
Although, a person skilled in the art may know it, the Inventors would like to provide a bnef descnption of the basic physics of cavity distension Filling the tissue cavity with fluid enables distension of the same Initially more fluid is pumped in than the amount which is extracted from the cavity and ultimately the mflow rate is fixed at a level where a somewhat desired cavity pressure and distension is achieved It may be possible to accurately maintain the desired pressure and distension in the case of a ngid cavity, for example a cavity made of steel
However, the body tissue cavities are not ngid because they are distensible and also have some element of elasticity Thus a distended tissue cavity in its attempt to constantly revert back to Its natural collapsed state reacts by exhibiting physiological contractions of the cavity wall which generally leads to vanations in the cavity pressure which ultimately culminates in irregular movement excursions of the cavity walls In a static system the said movement excursions may be so minute that they may even go unnoticed However in a dynamic system such that being created dunng an endoscopic procedure, the said physiological cavity wall contractions may cause the cavity to expel out its entire fluid content thus leading to a surgically dangerous large magnitude movement excursion of the cavity wall Because of these reasons it is extremely difficult to mamtain the cavity pressure and cavity distension in a predictably stable fashion
Further, the inflow tube, the out flow tube and the endoscope also mvanably move and shake dunng surgery which leads to vanations in fluid flow resistance which is also manifested in the form of vanations in the cavity pressure The cavity pressure vanations occumng as a result of cavity wall contractions and the mechanical movement of the tubes and the endoscope tend to occur again even if they are corrected once because it is impossible to prevent the physiological cavity wall contractions and the mechanical movements of the imgation circuit Thus, the said cavity pressure vanations shall continue to occur even after multiple repeated corrections
Thus, till date the surgeon was only left with two options, either to ignore the said cavity pressure vanations by not correctmg them, or to externally and actively correct such pressure vanations The Inventors have noticed that any attempt to externally and actively correct the said cavity pressure vanations leads to an undesirable turbulence inside the cavity and also tends to amplify the resultant movement excursions of the cavity walls Thus there is a grave need to provide a system which can maintain an almost constant and stable cavity pressure even in the presence of the said physiological cavity contractions and the mechanical movements m the imgation circuit BRIEF DESCRIPTION OF AN ENDOSCOPE:
Pnor to descnbmg the basic layout of a continuous flow imgation system the basic structure of an 'endoscope' needs to be descnbed Endoscope is a cyhndncal tube having an outer diameter ranging between 3 to 9 mm approximately A typical endoscope has four channels One channel is meant to pass a fibereoptic telescope while endoscopic instruments are negotiated through a second instrument channel A third channel also known as the inflow channel is used for pushing imgation fluid into a tissue cavity, the proximal end of this channel ending m a metal adaptor known as the inflow port while the distal end of this mflow channel opens near the tip of the endoscope The inflow port is connectable to an inflow tube which cames stenle imgation fluid from a fluid source reservou" A fourth channel also known as the out flow channel is meant for extracting waste fluid out of the cavity, the proximal end of this channel ending in a metal adaptor known as the outflow port while the distal end of this outflow channel opens near the tip of the endoscope The outflow port is connectable with an outflow tube which transports the waste fluid from the cavity to a suitable waste fluid collecting reservoir A set of fiber optic bundles contained inside the telescope transmit light energy produced by an external light source This light energy illummates the walls of the tissue cavity The image thus formed is earned via a separate set of optical pathways again situated inside the telescope A video camera attached to the eye piece of the telescope forms a clear endoscopic image of the cavity on a TV monitor. The endoscopic surgeon has to continuously look at the TV monitor all through the endoscopic procedure
BASIC LAYOUT OF A 'CONTINUOUS FLOW IRRIGATION SYSTEM: Henceforth in this manuscnpt unless otherwise specified the term 'distension' shall be deemed to imply tissue cavity distension by 'continuous flow imgation' only and the term 'cavity' unless specifically stated shall be deemed to refer to a 'body tissue cavity' In a typical distension system a physiological non viscous liquid like 0 9% normal saline, 1 5%
glycme, mannitol, nnger's lactate and 5% dextrose is stored in a stenle fluid source reservoir A fluid supply tube connects the said fluid reservoir with the inlet end of a pump The outlet end of the inflow pump is connected to the mflow port of an endoscope When the inflow pump operates the fluid from the fluid source reservoir is sucked via the fluid supply tube and the mflow pump pushes this fluid into the tissue cavity via the said mflow tube The pump operates by consuming certam amount of energy and as a result of this a positive fluid pressure is created mside the tissue cavity An outflow tube extends between the outflow port and the inlet end of an outflow pump When the outflow pump operates it actively extracts waste fluid from the cavity again at the expense of energy and this waste fluid is ultimately sent to a waste fluid reservoir via a tube which connects the outlet end of the outflow pump with the waste fluid reservoir Alternatively the outflow pump may be missing and m such case the outflow tube directly carries the waste fluid from the cavity to the waste fluid reservoir and the energy for such act is supplied by gravity instead of the outflow pump Also, the inflow pump may be missing and in such case die inflow tube directly supplies the irrigation fluid from a fluid source reservoir to the cavity In such case the fluid source reservoir is hung at a suitable height above the patient and the said energy for cavity distension is derived from gravity instead of the inflow pump A suitable pressure transducer is attached to the mflow tube, the outflow tube or directly to the cavity to measure the fluid pressure A controller may be incorporated to regulate the system THE SIMPLEST CONTINUOUS FLOW IRRIGATION SYSTEM: In Its simplest form, a contmuous flow imgation system comprises a fluid reservoir bottle hung at a suitable height above the patient and an inflow tube connectmg this fluid reservoir to a tissue cavity An out flow tube is incorporated to remove fluid from the tssue cavity. In this system there is no pump and no transducer In such a system fluid flows from the fluid source reservoir mto the cavity and the required energy is supplied by gravity The pressure developed inside the cavity can be mcreased or decreased by elevatmg or lowermg the height of the fluid source reservoir In such system the mam limiting factor is the height of the room ceilmg beyond which the fluid reservoir cannot be raised This is a crude system having negligible practical importance and has been mcluded only from the academic pomt of view Also m such a system unlimited volume of imgation fluid may enter mto the patient's blood circulation Thus such system is not suitable even from the patient safety point of view BASIC COMPONENTS OF A CONTINUOUS FLOW IRRIGATION SYSTEM: Like a motor car is made up of certain obvious components like engine, testes and a steenng wheel, a continuous flow distending system is made of components like pump, pressure
transducer, flow regulating valve, rubber tubes and a controller The pump may be a positive displacement pump like a peristaltic pump, piston pump or a gear pump or alternatively it may be a dynamic pump like a centnfugal pump Further the said pump may be of a fixed RPM type which runs at fixed RPM all through the endoscopic procedure or the pump may be of a variable RPM type which operates at vanable RPM dunng the endoscopic procedure It is extremely important to note that fixed RPM pumps and vanable RPM pumps are two separate mechanical entities m context with a cavity distending system because the fixed and vanable RPM pumps impart different surgical efficiency and patient safety cntena to the distending system The said pump may be attached on the inflow side only, on the outflow side only or both on the inflow and outflow side Further if a pump is attached only on the mflow side the outflow tube may directly empty in a waste fluid reservoir at atmosphenc pressure or a vacuum source may also be additionally attached In some distending systems a flow controlling valve is attached on the outflow tube in order to regulate the cavity pressure There may be a single pressure transducer attached to the inflow tube, the outflow tube or directly to the cavity In some systems instead of one pressure transducer two pressure transducers may be used, one on the inflow tube and the other on the outflow tube DESCRIPTION OF A PRIOR ART SYSTEM USING A PNEUMATIC PUMP ON THE INFLOW SIDE
This type of system has been descnbed m U S Pat No 5814009 (Wheatman) This patent is related to product Dolphin II Fluid Management System marketed by ACMI CIRCON In this system the irrigation fluid is pushed into the utenne cavity by the help of a bladder pump which compresses the imgation fluid contained in a collapsible plastic container The outflow tube opens directly into a waste fluid collecting container at atmosphenc or m a waste fluid collecting container having a vacuum source attached to it In this system a pressure transducer located in the downstream portion of the inflow tube near the inflow port constantly senses the cavity pressure and sends appropnate signals to a controller which by a feedback mechanism regulates the air pressure inside the bladder enclosmg the said collapsible fluid source container If the said pressure transducer senses a fall m the tissue cavity pressure it sends a feedback signal to the said controller via a feedback mechanism and the controller m turn increases the air pressure mside the said bladder by activating an air compressor which results in the collapsible fluid source container being compressed with a greater force which culminates in an increased inflow rate and the end result being an mcreased uterine cavity pressure. Similarly when the utenne cavity pressure increases the controller causes the bladder pressure to decrease and the end result being a reduced utenne
cavity pressure In this system the cavity pressure is maintained by irregularly fluctuatmg around a preset value, thus implying that in the said system the pressure cannot be maintamed at a fixed and precise value The differences between this system related to U S Pat No 5814009 and the system of the proposed mvention are given below in table 1 Table 1. Comparison of the System of Wheatman et al (U S Pat No 5814009) with the system of the proposed invention

(Table Removed)

Relvant references have been included in a PCT application filed by the Inventors m the past numbered PCT/IB/002341 and the same may also be deemed to have been included in the present application In addition, three references U S Pat Nos 5520638, 4902277 and 5578012 are now being included and discussed herebelow

In the U S Pat No 5520638 a vanable speed penstaltic pump is used to push irrigation fluid mto a tissue cavity This patent is related to the 'Continuous Wave II Arthroscopy Pump' marketed by Arthrex A chamber with volume is connected to the inflow tube and a collapsible bladder is contained withm the bladder. The collapsible bladder has an open end connected with tubing to a pressure transducer. Once activated the pump begins to mtroduce fluid into the tissue cavity via the inflow tube and as pressure builds within the tissue cavity, fluid enters the chamber, and air in the chamber is compressed The compressed air in the chamber compresses the bladder Air pressure m the bladder is expenenced by the pressure transducer. The pressure transducer feeds pressure mformation to a controller which regulates the RPM of the pump on the basis of a pressure feedback mechanism Thus by the help of a pressure feedback mechanism the pressure inside a tissue cavity is maintained by fluctuatmg around a desired value In this invention an important purpose of the said chamber is to dampen the pressure pulsations created by the peristaltic pump Such pressure pulsations create turbulence inside the tissues cavity and are hence undesirable The method of dampening the pressure pulsations as descnbed in this 5520638 is not adequately efficient, especially at high pump RPM's. The Inventors would like to submit that the system bemg claimed m the aforesaid US Patent is a passive dampening system The system is only able to passively correct the small pressure pulsations In the present invention a method shall be descnbed by which the amplitude of the said pressure pulsations would be reduced to negligible magnitude even at a high pump RPM
In U S Pat No 4902277 a pump is provided on the mflow side which pushes fluid into a tissue cavity while a positive displacement pump removes fluid from the cavity This patent is related to 'FMS duo Fluid Management System' marketed by FMS Group. By the help of a pressure feedback mechanism the inflow pump is constantly mcreased or decreased thereby mamtammg the cavity around a desired value Thus by the help of a pressure feedback mechanism the pressure inside a tissue cavity is mamtained by fluctuating around a desired value
In U.S Pat No 5578012 a centrifugal pump is deployed on the inflow side while no pump is deployed over the outflow side This patent is related to the 'HydroFlex HD' pump marketed by DA VOL company By the help of a pressure feedback mechanism the mflow pump is constantly increased or decreased thereby maintaining the cavity around a desired value. Thus by the help of a pressure feedback mechanism the pressure inside a tissue cavity is maintained by fluctuating around a desired value.
Inventors own PCT Application No PCT/IB04/002341 filed on 21/07/2004 and the contents of the same may also deemed to be included m the present application and could be referred to as and when found necessary
OBJECTS OF THE INVENTION
The overall objective of the mvention is to provide a safe, efficient and turbulence free
system for distending body tissue cavities for those endoscopic procedures which utilize
contmuous flow imgation
The main object of the invention is to mmimize the amplitude as well as the fi-equency of
pressure pulsations, mside the tissue cavity, created by the two positive displacement pumps
Another object of the present mvention is to provide a system for distending tissue cavities
usmg which it being possible to create and maintam a desired precise cavity pressure for a
desired precise rate at which fluid may be allowed to flow through the cavity, for any length
of time
Still another object of the present invention is to provide a system for distendmg tissue
cavities using which it being possible to achieve a predictably constant clear endoscopic
vision throughout the endoscopic procedure
Yet another object of the present invention is to provide a system for distendmg tissue
cavities using which it being possible to achieve predictably stable mechanical cavity
distension throughout the endoscopic procedure
One more object of the present mvention is to provide a system for distending tissue cavities
using which it being possible to predictably mamtam the cavity pressure at any desired
precise value despite physiological contractions of the cavity wall
One another object of the present invention is to provide a system for distendmg tissue
cavities using which it bemg possible to constantly, accurately and rehably determine the
instantaneous real time rate of fluid intravasation into the patient's body by usmg two fluid
flow rate sensors which do not have any movable components
A further more object of the present mvention is to provide a system for distending tissue
cavities usmg which it being possible to maintain any desired precise and high cavity
pressure without increasing the 'maximum possible fluid mtravasation rate'
Another object of the present mvention is to provide a system for distending tissue cavities
using which it being possible to measure the actual cavity pressure, m an accurate, reliable
and simple manner, by using a pressure transducer located far away from the cavity in the up
stream portion of the inflow tube
Yet another object of the present invention is to provide a system for distending tissue cavities using which it being possible to make the pressure mside the body cavity and the flow rate of the fluid passing through the body cavity absolutely mdependent of each other such that the value of any may be altered without affecting the value of the other Still another object of the present invention is to provide a system for distending tissue cavities using which it being possible to reduce the cavity filling time m a predictably controlled manner and at the same time achieving a desired cavity pressure at the end of the cavity refilling phase, cavity refilling time being the time taken to completely fill a cavity with the irigation fluid
One more object of the present invention is to provide a system for distending tissue cavities using which it being possible for the surgeon to have a fairly accurate assessment of the total volume of the imgation fluid which would be required to complete the entire endoscopic procedure
On another object of the present invention is to provide a system for distending tissue cavities usmg which it being possible for the surgeon to accurately know the maximum pressure which develop inside the cavity in case of an accidental obstruction of the outflow tube and it should be possible to minimize such nse m the cavity pressure m a controlled and predictable manner
SUMMARY OF THE INVENTION
The present mvention provides a safe and an efficient system for distending body tissue cavities for those endoscopic procedures which utilize continuous flow imgation The mam aim of the invention is to mmimize cavity fluid turbulence by minimizing the amplitude as well as the frequency of the pressure pulsations in a tissue cavity created by two positive displacement pumps. The present mvention is a system of creating and mamtammg a desired positive pressure mside a body tissue cavity through which fluid is made to flow at a desired flow rate Alternatively the present invention may be considered as a system of creatmg cavity fluid pressure which is absolutely independent of the cavity outflow rate The present invention comprises of two positive displacement pumps which work simultaneously, for mdefimte time, at fixed flow rates to create and maintain any precise desired cavity pressure for any desired cavity outflow rate, mcluding a zero outflow rate The present invention compnses of a dynamic pump like a pneumatic piston pump on the mflow side and a positive displacement pump such as a penstaltic on the outflow side which work simultaneously, for mdefimte time, at fixed RPM's to create and maintain a desired precise cavity pressure for a desired cavity outflow rate In the present invention the amplitude of tissue cavity pressure
fluctuations caused by two positive displacement outflow and inflow pumps can be
minimized to almost negligible levels Also m the proposed invention the changes in the
tissue cavity pressure is not actively corrected as is done in the pnor art systems Further if
any fluid is being absorbed mto or through the cavity walls, such as fluid mtravasation which
occurs dunng hysteroscopic endometnal resection, the instantaneous real time rate of such
fluid absorption can be constantly determined by utilizmg two fluid flow rate sensors Also
the cavity pressure can be mamtained at any desired high value without mcreasing the
'maximum possible fluid mtravasation rate' In the proposed invention by synchronizing the
mflow and the outflow pumps it is possible to reduce fluid turbulence to almost negligible
levels The proposed invention also has multiple other features of endoscopic surgical
relevance which greatly enhance the patient safety and efficiency dunng endoscopic surgery
few such features being shortening of the cavity refilling time in a predictably controlled
fashion, to be able to predict by a fair degree of accuracy the volume of fluid which would be
required to complete the endoscopic procedure, to be able to predict and limit the magnitude
of the maximum mcrease in the cavity pressure or the magnitude of a minor pressure surge
which might occur in case of an accidental obstruction of the outflow tube for a specific
outflow rate Also the same system can be used for all types of endoscopic procedures which
utilize continuous flow imgation
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows the mam invention with a pressure pulse dampening system
Figure 2 is similar to figure 1 except that the pressure pulse dampenmg system has not been
included
Figure 3 is similar to figure 2 except that the controller has not been included.
Figure 4 is the same as figure 3 except that a fluid replemshmg tube, an optional transducer
on the outflow side and an optional constriction site housmg tube have been included
Figure 5 shown a special type of coupling mechanism to operate the syringe system.
Figure 6 is similar to the main invention shown in figure 1 except that m figure 6 a pressure
pulse dampening system has been added on the inflow side also
Figure 7 shows a detailed layout of the outflow pressure pulse dampening system
DETAILED DESCRIPTION OF INVENTION
Accordingly, the present invention provides a system for distendmg body tissue cavities of
subjects by continuous flow imgation dunng endoscopic procedures the said system
compnsing
a collapsible fluid source reservoir containing a non viscous physiologic fluid meant for
tissue cavity distension,
said fluid source reservoir being encircled by a bladder cavity, said bladder cavity being
connected to an inflow positive displacement pump through an air transporting tube for
inflating the same and a pressure transducer being coupled to the air transporting tube,
a fluid supply mflow tube connecting the fluid source reservoir to an inflow port of an
endoscope mstrument for pumping the fluid at a controlled flow rate mto the body tissue
cavity, the flow rate of the said inflow pump being termed as the inflow rate and the rate at
which the fluid from the mflow tube enters into the tissue cavity bemg termed as the cavity
inflow rate,
an inflow liquid pressure transducer bemg coupled to the fluid supply conduit tube,
an outflow port of the endoscope being connectable to an mlet end of a vanable speed
positive displacement outflow pump through a outflow tube for removing the fluid from the
cavity at a controlled flow rate, the flow rate of the said outflow pump bemg termed as the
cavity outflow rate,
an outlet end of the outflow pump bemg connected to a waste fluid collecting container via a
waste fluid carrymg tube, and
charactenzed that a housing tube having a controllable constnction site is bemg coupled to
the air transporting tube between the positive displacement inflow pump and the bladder
cavity, wherem the housmg tube provides a route for any excess air present m the bladder
cavity or being pumped by the positive displacement pump to escape to the atmosphere,
thereby minimizing turbulence inside the body tissue cavity and mamtaining the body tissue
cavity pressure at a stable value despite physiological contractions of the body tissue cavity
wall
In an embodiment of the present invention, a proximal end of the fluid supply conduit tube is connected to the fluid source reservoir and a distal end of the tube bemg connectable to the mflow port of the endoscope instrument
In another embodiment of the present invention, the positive displacement mflow pump is a piston pump
In yet another embodiment of the present invention, the housmg tube is releasably provided between the positive displacement pump and the bladder cavity to enable replacement of the housing tube with yet another housmg tube having a different diameter at the constriction site to suit the operational need of the endoscopic procedure
In still another embodiment of the present invention, the housing tube is provided with a clamping means at the constriction site to enable the user to vary the diameter of the housmg tube at the constnction site to suit the operational needs of endoscopic procedures
In one more embodiment of the present invention, the diameter of the housmg tube at the constriction site is in the range of 0 001 mm to a maximum value which is less than the overall diameter of the rest of the housing tube
In one another embodiment of the present invention, the diameter of the housmg tube at the constnction site is in the range of 0 01 to 2 5 mm
In a further embodiment of the present mvention, the mflow pressure transducer is located sufficiently away from the cavity site, preferably near the outlet end of the mflow pump from the practical pomt of view, such that the fluid pressure measured by the same is almost equal to the fluid pressure inside the cavity
In a further more embodiment of the present invention, a proximal end of the outflow tube being connectable to the outlet port of the endoscope mstrument and a distal end of the outflow tube is connected to an inlet end of the vanable speed positive displacement outflow pump
In another embodiment, the system of the present mvention further compnses an inflow gas pressure transducer connected between the positive displacement pump and the bladder cavity
In yet another embodiment, the system of the present invention further comprises an outflow pressure transducer connected between a proximal end of the outflow tube and the inlet end of the vanable speed positive displacement outflow pump for measunng the pressure m the outflow tube
In still another embodiment of the present mvention, the vanable speed positive displacement outflow pump is selected from the group compnsing penstaltic pump, piston pump, gear pump, diaphragm pump and plunger pump
In one more embodiment of the present mvention, the vanable speed positive displacement outflow pump is a penstaltic pump
In one another embodiment of the present invention, the outlet end of the vanable speed positive displacement outflow pump is connected to the waste fluid collecting container through a waste fluid carrying tube
In yet another embodiment, the system of the present invention further compnses a microcontroller means electrically coupled to the inflow gas pressure transducer, the inflow liquid pressure transducer, the outflow pressure transducer, the inflow positive displacement pump and the outflow pump for regulating the operation of the inflow and the outflow pumps.
In still another embodiment of the present invention, the housing tube is provided with an electromechanical device, a solenoid, to enable the micro-controller to vary the diameter of the constnction site
In one more embodiment, the system of the present invention further compnses a housing tube having a vanable size constnction site being provided between the outflow tube and the waste fluid reservoir
In one another embodiment of the present invention, a proximal end of the housmg tube is connected to the outflow near the inlet of the outflow pump
In an embodiment, the system of the present invention further comprises a fluid replenishing tube connected either directly or indirectly to the fluid source reservoir through a replenishment fluid controllmg valve for refilling the fluid source reservoir
In another embodiment of the present invention, the fluid replenishing tube is connected directly to the fluid source reservoir or via the fluid supply inflow tube to the fluid source reservoir
In yet another embodiment of the present invention, an inflow fluid controlling valve is provided on the mflow tube for preventing the fluid from entenng into the tissue cavity dunng fluid replenishment phase
In still another embodiment of the present invention, the fluid supply conduit tube and the outflow tube and the waste fluid carrying tube are flexible, disposable and are made of polymenc matenal
In one more embodiment, the system of the present invention further compnses a fluid inflow rate sensor connected to the inflow tube
In one another embodiment of the present invention, the fluid inflow rate sensor is located m the lumen or wall of the inflow fluid supply conduit tube for measurmg the cavity inflow rate In another embodiment, the system of the present invention further comprises a fluid outflow rate sensor connected between the proximal end of the outflow tube and the mlet end of the vanable speed positive displacement outflow pump for measunng the cavity outflow rate.
In yet another embodiment of the present invention, the fluid inflow and the outflow rate sensors consist of a heating coil m physical contact with a metal plate for heatmg the same and a temperature sensor placed in contact with the metal plate for measunng the temperature of the said metal plate, the temperature of the metal plate being a function of the fluid flow rate
In still another embodiment of the present invention, the fluid rate flow sensor is a hot wire anemometer
In one more embodiment of the present invention, mstantaneous real time rate of fluid mtravasation is determmed by electrically connecting the inflow and outflow fluid flow rate sensors to a micro-controller
In one another embodiment, the system of the present invention further comprises an mflow pressure vanation dampenmg means provided on the inflow side for dampening the pressure variation inside the body tissue cavity caused by the positive displacement mflow pump.
In one further embodiment of the present invention, the mflow pressure variation dampening means composes a single outlet synnge mechanism, the piston of the same bemg coupled synchronously to the positive displacement mflow pump through a coupling means and the smgle outlet end of the said synnge mechanism being connected to the air transporting tube.
In another embodiment, the system of the present invention further compnses an outflow pressure vanation dampening means provided on the outflow side for dampenmg the pressure vanation mside the body tissue cavity caused by the positive displacement outflow pump
In yet another embodiment of the present invention, the outflow pressure vanation dampenmg means compnses a single outlet synnge mechanism, the piston of the same being coupled synchronously to the positive displacement outflow pump tiirough a coupling means and the single outlet end of the said synnge mechanism being connected to the outflow tube
The present invention also provides a method of distending a body tissue cavity of a subject by continuous flow imgation such that minimal or negligible fluid turbulence is present inside the cavity, such that any desired cavity pressure can be created and mamtamed for any desired outflow rate, said method compnsmg the steps of
(a) mflatmg a bladder cavity that encircles a collapsible fluid source reservoir using a positive displacement pump for dispensing a non viscous physiologic fluid meant for cavity distension from the fluid source reservoir to an inflow port of an endoscope instrument at a controlled flow rate tiirough one or more fluid supply conduit tubes;
(b) mjecting the non- viscous physiologic fluid at a controlled flow rate into the cavity for distending the body tissue cavity of the subject, the rate at which the fluid enters into the tissue cavity firom via the mflow fluid conduit being termed as the cavity mflow rate,
(c) removing a waste fluid from the cavity via the outlet port of the endoscope,
(d) actively extracting the waste fluid via the outlet port of the endoscope and transporting it to a waste fluid collecting reservoir at a controlled flow rate, the said flow rate being termed as the cavity outflow rate, through a outflow conduit tube, a vanable speed positive displacement outflow pump and a waste fluid carrying tube and
(e) providing a housing tube having a controllable constriction site between the bladder cavity and the positive displacement inflow pump such that the housing tube provides a route for any excess air being pumped by the positive displacement pump or due to the physiologic contraction of the body tissue cavity walls escape to the atmosphere, thereby avoiding turbulence mside the body tissue cavity and to mamtam a stable pressure inside the body tissue cavity
The proposed mvention is descnbed hereafter with reference to the accompanying drawmgs m order to clearly explain and illustrate the system and the working of the system It is respectfiiUy submitted the scope of the invention should not be limited by the descnption being provided hereafter
The system of the present invention is a unique system for distendmg body tissue cavities m endoscopic procedures In the proposed mvention a body tissue cavity is distended by contmuous flow imgation m such a manner that the amplitude of the pressure pulsations created by a positive displacement outflow pump and a positive displacement, mflow pneumatic piston pump, can be reduced to a negligible value In the proposed mvention a method of reducing of the said pulsations has been descnbed. Also the cavity pressure is absolutely independent of the cavity outflow rate, such the both, the cavity pressure and the outflow rate, may be independently altered without varymg the value of the other parameter Figure 1 shows the mam diagram of the invention In figure 1 an outflow 'pressure pulse dampening system', has been shown clearly However m order understand the invention m a simpler manner, first the basic mvention without the said 'pressure pulse dampenmg system' shall be discussed by takmg the help of figures 2 and 3 Figure 3 is similar to figure 2 except that in figure 3 a controller 25 in not included, and the said 'pressure pulse dampening system is also not shown in figures 2 and 3 as already stated The two pumps 3 and 20 operate simultaneously in order to distend a tissue cavity in such a manner that the cavity pressure is totally independent of the cavity outflow rate
Refemng to figure 2 a positive displacement pump, preferably a piston pump 1 is used to for mstilling air into a bladder cavity 9 This pump in the form of a piston pump 1 installed on the inflow side of the imgation circuit shall be termed as 'pneumatic pump' m the rest of the manuscnpt The pump 1 shall also be referred to as the 'inflow pump' as it is located on the inflow side of the imgation circuit A positive displacement pump, preferably a penstaltic pump 20 is attached on the outflow side of the imgation circuit. The two pumps 1 and 20 can operate simultaneously in order to distend a tissue cavity m such a manner that the cavity pressure is totally independent of the cavity outflow rate. Please note that the controller bemg used in the system shown in figure 1 is an optional feature and the system would provide most of the features even without the controller The figure 3 represents the schematic diagram of the invention but without a controller system Thus figure 3 is a mechanical version of the invention A human operator is required to operate such mechanical version of the invention shown in figure 3 Though it is recommended that the controller based version of the invention be used in endoscopic surgenes, it is not essential The controller being used m the present invention merely assists the user in amving easily at some of the additional functions which otherwise can be performed manually Thus, in tins manuscnpt the mechanical version of the invention shown m figure 3 is being discussed m more detail m order to explain the basic physical pnncipals of the invention with a greater clanty Refemng to figure 3, the system shown m this figure compnses of a pneumatic pump and a peristaltic pump which can maintain a predictably precise stable cavity pressure for indefinite time by workmg simultaneously at fixed RPM's. Pneumatic pump 1 pushes air into a bladder cavity 9 which encloses a suitable collapsible plastic fluid source container 10 which contains stenle non viscous physiological fluid like 0 9% normal saline, 1 5% glycine, nnger lactate or 5% dextrose fluid When the pneumatic pump 1 operates air flows mto the bladder cavity 9 via a air transporting tube 4 which creates a positive pressure mside the bladder cavity 9 which compresses the fluid contained in the fluid source contamer 10 which causes the pressunzed irrigation fluid to be expelled out of the fluid source container 10 and this ungation fluid flows mto the tissue cavity 15 via an inflow tube 11 The out flow peristaltic pump 20 simultaneously extracts fluid out of the tissue cavity 15 via an out flow tube 18. A constnction site housing tube 7 is attached anywhere to the air transporting tube 4, such as at a point 6 The said constnction site housing tube 7 has a constriction point 8 which can be located anywhere along its length Such constnction point refers to a point where the inner diameter of the lumen of tube 7 is reduced in companson to the lumen of the rest of the tube 7 One end of tube 7 is connected to the air transporting tube 4 while the other end just opens
mto the atmosphere Such constriction may be a permanent constnction in the lumen of tube 7 or It may be a vanable constriction whose diameter may be mcreased or decreased as desired A suitable pressure transducer 5 connected anywhere to the air transporting tube 4 via a tube 23, such as at point 6, measures the air pressure in the bladder cavity 9 The bladder cavity 9 is assumed to be absolutely distensible but not elastic A pressure transducer 14 is attached at one of tube 24 while the other end of tube 24 is connected anywhere on mflow tube 11 For practical convenience it is desirable that the said other end of tube 24 be connected m the up stream part of the inflow tube 11 such as at point 26 For practical convenience the point 26 may be located in the pump housing itself The pressure transducer 14 measures the fluid pressure via a column of liquid or air present m the lumen of tube 24 The fluid pressure as measured by the pressure transducer 14 shall be referred to as P In this manuscnpt the term 'P' shall frequently be used to refer to the actual pressure mside the tissue cavity but in physical terms P is the pressure sensed by the transducer 14 at point 26 The pressure transducer 14 may also be in the form of a membrane diaphragm incorporated in the wall of the inflow tube 11 such that this membrane diaphragm is in direct contact with the fluid contamed in the mflow tube 11, such that the linear movement excursions of the said membrane are interpreted as pressure of the fluid inside the inflow tube 11 by a suitable pressure transducer Such type of pressure sensor bemg directly incorporated m the wall of the mflow tube 10 senses the fluid pressure without the intervention of tube 24. The basic purpose of the transducer 14 is to measure the fluid pressure mside the inflow tube 11, such as at point 26, thus the mechanical construction of the transducer is not important as long as it measures the fluid pressure For the sake of simplicity the existence of tube 24 shall be continued to be considered in the rest of the manuscript The peristaltic pump 20 attached to the outflow side actively extracts fluid out of the tissue cavity 15 via the out flow tube 18 The outlet end of the pump 20 is connected to a waste fluid carrying tube 21 which opens mto a waste fluid collecting reservoir 22 at atmosphenc pressure. The rollers of the pump 20 constantly compress and roll over the entire length of the peristaltic pump tubing 19 thus displacing fluid in the direction of the curved arrow which also corresponds with the direction of pump rotation.
In order to understand the mvention m a simpler manner all the tubes shown m figure 3 and the inflow and out flow port are considered to be having the same uniform inner diameter However the inner diameter of the tubes and the mflow and outflow ports can also be different The inflow and outflow ports are metallic adaptors located at the proximal end of the endoscope and are meant to connect with the inflow and outflow tubes respectively,
however the said inflow and outflow ports have not been separately shown in any of the figures Tube 19 consists of a soft resilient plastic matenal which can be efficiently compressed by the rollers of the peristaltic pumps The other tubes also consist of a suitable resilient plastic matenal It is assumed that the bladder 10 along with the fluid container 10, the inflow tube, the cavity, the out flow tube and the out flow peristaltic pump are placed at the same honzontal height with respect to the ground The bladder cavity enclosing the container 10 can also be hung on a stand at a suitable height above the patient but in this case the additional pressure as a result of the fluid column m the mflow tube 11 also has to be taken into account Thus for an easier understanding bladder cavity 10, the inflow tube 11, the cavity 15, the out flow tube 18 and pump 20 shall be assumed to be at the same honzontal height with respect to the floor Also the rollers of pump 20 should press adequately over tube 19 in such a manner that there is no leak through this tube when the pump 20 is stationary It is also assumed that there is no abnormal leak of fluid in the imgation system, for example leak via a accidental hole made m any imgation tube or a fluid leak which might occur if the endoscope loosely enters mto the tissue cavity, for example in hysteroscopic surgery fluid leaks by the sides of the endoscope if the cervix is over dilated Also a constnction site housing tube similar to tube 7 labeled as 31 can be attached to the outflow tube 18 as shown in figure 4 In the said tube 31 the said constriction site is labeled as 32. Such tube can serve a number of purposes Tube 31 can be utilized for relatively faster evacuation of air bubbles from the cavity The said bubbles are mvariably created mside the cavity as a result of electrosurgical cutting and coagulation or they may enter the cavity while the endoscope is bemg introduced mto the cavity Such bubbles cause extreme nuisance for the surgeon because they obscure vision and thus the surgical time may be greatly mcreased In routine surgery the surgeon moves the tip of the resectoscope near the bubble and the bubble is sucked out of the cavity by the process of contmuous flow imgation However m certain situations it may not be possible to bnng the tip of the resectoscope near the bubble, one such situation is when bubbles accumulate inside a very deep comuae associated with a long septum, the diameter of the comuae bemg less than the outer diameter of the resectoscope In such a situation the tubal opening situated at the center of the comuae can only be visualized after evacuating such bubbles from the cavity In such situation the bubbles can be quickly evacuated without moving the tip of the resectoscope near the bubbles by simply opening the constnction 32 m the tube 31 However such maneuver tends to completely collapse the cavity Thus if the resctoscope tip is only moderately away from the bubbles the constnction site 32 is opened only partially so that the bubbles are sucked out and
the cavity collapses by a relatively smaller magnitude In place of the adjustable constnction site 32 a pressure release safety valve may be incorporated as a safety feature, however it is more beneficial to install such pressure safety valve in the inflow circuit The tube 31 may also be used for quickly flushing air bubbles from the imgation tubes by fully opening the constnction site 32 for a few seconds The tube 31 may also be used for any other purpose as deemed fit by the surgeon However the said tube 32 has intentionally not been mcluded m figures 1 to 3 only to keep the drawings simple However tube 31 is a very beneficial component and is thus recommended to be mcorporated in the system of the proposed invention The opening and closing of the constnction site 32 can also be regulated manually to help in vanous special advanced endoscopic applications Incorporation of tube 31 with the vanable constnction site 32 can help in reducing the substantially high amplitude pressure vanations mside the cavity caused by abnormally large cavity wall contractions, but such phenomenon is only rarely encountered Also an additional pressure transducer 30, as shown in figure 4, may also be attached on the out flow tube 18, if desired, as shown m figure 4 However the said pressure transducer 30 has intentionally not been included m the main block diagrams of the invention because by doing so it would have become very difficult to explain the basic physical pnncipals of the mvention Also a fluid replenishmg tube 27 with a flow controlling valve or clamp 28, as shown m figure 4 can also be incorporated A flow controllmg valve or clamp 29, as shown in figure 4, can also be incorporated m the inflow tube 11 The function of the said 27, valves 28 and 29 shall be descnbed in the subsequent paragraphs The said fluid replenishing tube can also be connected directly to the fluid source reservou- 10 and such tube has been labeled as 33 and the related flow controlling valve has been labeled as 34
In order to clearly understand the system shown m figure 3 it would be helpful to first discuss the functioning of the inflow pneumatic pump 1 As abeady mentioned the pneumatic pump 1 is a piston pump Initially when the pump 1 is not operating the tubes 4, 23, 7 and the bladder cavity 9 contain air at atmosphenc pressure When the pump 1 is operated air starts entenng into tubes 4, 23, 7 and the bladder cavity 9 The moment the constnction site 8 is fully occluded air starts accumulating inside tubes 4, 23, the bladder cavity 9 and a part of tube 7 between point 6 and the constnction site 8 If tube 7 continues to remain fully occluded at the constnction site 8, the air continues to accumulate mside tubes 4, 23, the bladder cavity 9 and a part of tube 7 between point 6 and the constnction site 8 and the pressure transducer 5 reads a steeply increasing air pressure The moment the block at the constnction site 8 is partially released air escapes in the form of a jet through the partially
open constriction opening 8 mto the atmosphere With the constriction openmg 8 being only partially blocked, if the pump 1 continues to work at constant RPM the air pressure ultimately gets stabilized at a fixed value provided the internal diameter of the constriction site 8 is not further varied The diameter D of the constnction site 8 ranges from a minimum non-zero value to a maximum value which is less than the overall diameter of the rest of the housmg tube 7 Henceforth m this manuscript the inner diameter of the constnction site 8 shall be deemed to be fixed at some predetermined value D, unless otherwise stated The fluid which is being expelled out of the fluid source container 10 is actually pulsatile in nature due to the pulsatile nature of the air pressure mside the bladder cavity 9 A system to dampen the pulsatile nature of the air pressure shall be descnbed m the later sections of this manuscnpt The pressure sensed by the pressure transducer 5 is equal to the pressure inside the bladder cavity 9, as it simulates a static system Further the pressure inside the bladder cavity 9 can be considered almost equal or slightly higher than the pressure inside the fluid source container 10 Due to factional resistance expenenced by the moving fluid the pressure at point 26, as sensed by the transducer 14, is always found to be higher than the actual pressure mside the tissue cavity 15 but the said pressure difference is so small that it may be neglected from the practical surgical point of view Also such pressure difference increases as the fluid flow rate increases In the out flow rate ranging between 0 to 500 ml/min such pressure difference is in the range between 0 to 2 mm Hg approximately The term 'out flow rate' is being referred to the flow rate of pump 20 Also, the said pressure difference remains constant all through surgery at any fixed outflow rate Though the said pressure difference is negligible but if desired its effect can also be totally negated by subtracting its value from the pressure readmg of the transducer In this manner, m endoscopic surgenes, it is possible to determine the actual cavity pressure by usmg the pressure transducer 14 located far away from the cavity This feature is of special relevance because m endoscopic procedures like hysteroscopy, arthroscopy and bram endoscopic surgery while it is important to know the actual cavity pressure but at the same time it is practically difficult to take a pressure measurement directly from the cavity
Refemng to figure 3 it shall be first descnbed as to how the system of the proposed invention can be used mechanically, that is witiiout a controller. The penstaltic pump 1 and the penstaltic pump 20 can be made to work at any fixed rotational speed The air flow rate of pump 1 and the fluid flow rate of pump 20 is directly proportional to the pump RPM or the pump rotational speed Thus any precise pump flow rate can be generated by selecting a suitable pump rotational speed The fluid flow rate of pump 20 shall henceforth be denoted
by R2 and shall be termed as the 'outflow rate' The air flow rate of pump 1 shall be denoted by Rl and shall be termed as the 'inflow rate' Here it is to be noted that the term 'inflow rate' Rl is not the inflow rate for the cavity 15, as might be suggested by the literary meanmg of the term 'inflow' Henceforth in the entire manuscnpt the term 'inflow rate' shall only be referred to the flow rate of the inflow pump 1 unless specifically mentioned However the term 'outflow rate' R2 does correspond to the literary meanmg of the term 'outflow' because R2 is equal to the rate at which fluid flows out of the cavity 15 The surgeon mitially decides an out flow rate R2 by selecting a suitable rotational speed for pump 20 Next the surgeon decides the maximum flow rate at which fluid could be allowed to enter into the tissue cavity via the inflow tube 11 and the inflow pump 1 is set to work at such flow rate or at a flow rate slightly lesser than this Intravasation is process by which fluid enters into the patient's blood circulation through the cut ends of blood vessels located m the cavity wall or enters into the patient's body, for example into the pentoneal cavity, as a result of an accidental perforation or escapes via patent fallopian tubes into the pentoneal cavity Thus 'intravasation' is a process by which the pressunzed imgation fluid enters into the patient's body system through the walls of the tissue cavity In case of a surgical accident like cavity wall perforation the fluid being squeezed out of the contamer 10 can enter into the patient's body at a rate shghtly less than the value Rl It is obvious that the maximum rate of fluid intravasation cannot exceed the value Rl In case of an accident like cavity wall perforation it may take some time before an abnormally high intravasation rate is discovered and m such time a dangerous quantity of fluid might enter mto the patient's body If the inflow rate Rl is kept at a relatively lower value then the volume of mtravasated fluid m case of such an accident would be low After fixing the values for R2 and Rl the system is started and the diameter of the constnction site 8 is gradually reduced As the diameter of the constnction site 8 is reduced air pressure starts building up mside the bladder cavity 10 as a result of which fluid starts flowing into the tissue cavity and the pressure inside the tissue cavity starts nsmg When the desired pressure is achieved inside the tissue cavity the diameter of the constnction site 8 is not reduced any fiirflier and is fixed The diameter at the constnction site is termed as "D" The constnction site may also be a plastic or metal piece which has a hole in the centre such that the diameter of the hole is permanently fixed at some value D If a constnction 8 has a permanently fixed diameter then only the flow rates, that is the RPM's, of pumps 1 and 20 have to be set before the system becomes operational
The Inventors here would like to discuss about the importance of incorporating the housing tube 7 with the constriction site and the non-obvious advantages provided by the housing tube 7 with the constriction site
As mentioned earlier, till date the surgeons were left with only two options, either to ignore the cavity pressure vanations by not correcting them, or to externally and actively correct such pressure vanations To externally and actively correct the vanations in the cavity pressure, controller was incorporated and the working of the pumps were essentially controlled by the controller Incorporation of the controller controlling the operation of the pumps did not provide any benefit The controllers used to activate the controlling action after the vanations in the cavity pressure had subdued Thus, the controlling action initiated by the controller instead of benefiting the surgeon leads to an undesirable turbulence mside the cavity and also tends to amplify the resultant movement excursions of the cavity walls The Inventors have noticed that if the controller continuously controls the operations of the pumps (either on the inflow side or on the outflow side), the cavity pressure continuously fluctuates around a preset value and it not at all possible to attain a constant value The Inventors believe that the controller provides proper corrective action (by continuously controUmg the operations of the pumps) only if the fluctuations m the cavity pressure are gradual and not highly instantaneous That is, if the quantitative nse/fall in the cavity pressure is over long time penod, the controller would be able to provide proper corrective action As the time penod to detect vanation m the cavity pressure and commence corrective action is ideally m the range of 2 to 4 seconds, if the quantitative nse/fall m the cavity pressure is over very short time penod, the suggested mechanism of providing a controller will be unsuitable Under such mstances, instead of providing any corrective action, the controller destabilizes the system and induces additional pressure fluctuations inside the cavity (because of commencing a corrective action at a delayed stage) Thus it takes very long time period for the system to once again get stabilized
The Inventors have surpnsingly found that by incorporating a housing tube 7 provided with a constnction site in the au: carrying tube 4 as descnbed above, inherently and passively corrects the pressure vanations due to physiological cavity wall contractions and the mechanical movement of the tubes and the endoscope and also limits the vanation m the size of the cavity The Applicants would like to highlight that it is important to control both the vanations in the pressure inside the cavity and the changes in the size of the distended cavity Large vanations in the pressure inside the cavity or the size of the cavity are detnmental to the surgical procedure In all the pnor art systems attempts were made to either control the
vanations in the pressure or the vanations in the cavity size But none of the pnor art document the need to control both the cavity pressure vanations and the cavity size vanations and hence failed to provide a safe and ideal system Dunng the contraction of the cavity, a minute quantity of the fluid is pushed out of the cavity If dunng tins stage the system does not provide a way for releasing the fluid being pushed out, the instantaneous pressure inside the cavity increases tremendously which is harmful to the patient On the other hand, if the amount of fluid being pushed out of the cavity is not checked/controlled, the changes in the size of the distended cavity are very high The incorporation of the housing tube having the constnction site for the first time in the present system controls both the vanations in the pressure inside the cavity and the changes m the size of the distended cavity If the cavity contracts some fluid enters the fluid source container 10 m a retrograde maimer which causes a minute increase in the volume of the container 10 which m turn reduces the volume of the bladder cavity 10 by a corresponding magnitude and the same is facilitated by the escape of an additional equivalent volume of air via the constnction site 8 Thus the housing tube having the constnction site indirectly provides a by-pass route for the fluid being pushed out of the cavity to go back to the fluid source reservoir 10 This avoids the mstantaneous pressure surge mside the cavity which is harmful to the patient The size of the diameter at the constnction automatically controls the amount of fluid passing through the housing tube, thereby controUmg the amount of fluid bemg pushed out of the cavity. Inclusion of the housing tube with the constriction site therefore mmimizes the instantaneous vanations in the size of the distended cavity
Alternatively if the cavity expands a suitable volume of fluid is sucked into the cavity from the fluid source container 10, and this is accompanied by a corresponding transient decrease m the flow rate at which air escapes via the constnction site 8 but if the magnitude of the said physiological expansion is more air may even be sucked into the cavity via the constnchon site 8 This implies that the constnction site 8 is helping in maintaining a stable cavity pressure despite physiological cavity wall contractions by suitably varying the magnitude as well as the direction of an imaginary air flow vector passing through the constnction site 8 CAVITY PRESSURE OR THE OUTFLOW RATE, BOTH CAN BE ALTERED INDEPENDENTLY WITHOUT VARYING THE VALUE OF THE OTHER PARAMETER:
Refemng agam to figure 3 an hypothetical endoscopic procedure is being considered where surgery is being performed at an outflow rate R2 and inflow rate Rl with the constnction 8 diameter being been fixed at some value D and a resultant cavity pressure P being created
maintained In such hypothetical situation as long as R2 and Rl are not altered the cavity pressure P remains predictably constant throughout surgery resultmg in a predictably stable mechanical distension of the tissue cavity walls which culmmates in constant clear visualization throughout the endoscopic procedure If m the said hypothetical procedure the cavity pressure needs to be increased without altenng the out flow rate R2 then all that is needed is to start mcreasing the value of Rl and stop domg so when the desired higher cavity pressure is achieved Similarly if the cavity pressure needs to be decreased without altenng the out flow rate R2 then Rl is decreased till the desired lower cavity pressure is attained In the said hypothetical endoscopic procedure if the outflow rate R2 needs to be mcreased without altenng the cavity pressure P then the value of R2 is mcreased by the desired magnitude but simultaneously the value of Rl is also increased by a similar magnitude Similarly, if the outflow rate R2 needs to be decreased without altering the cavity pressure P then the value of R2 is decreased by the desired magnitude but simultaneously the value of Rl is also decreased by a similar magnitude Thus if Rl and R2 are simultaneously increased or decreased by the same magnitude the cavity pressure does not vary, the value D is always fixed as akeady stated. The preceding statements shall now be explained by the help of a numencal hypothetical example In reference to figure 3 considenng a hypothetical situation m which an endoscopic procedure is being done at an outflow rate of 100 ml/mmute, an mflow rate Rl and the cavity pressure bemg 80 mm Hg If the surgeon wants to increase the outflow rate to 322 ml/mmute by maintammg the cavity pressure at the same value of 80 mm Hg outflow rate is increased to 322 ml/mmute and the inflow rate is increased by 222 ml/minute, because 322 ml/min - 100 ml/mm = 222 ml/minute As already mentioned m this paragraph if both inflow and outflow rates are increased or decreased by the same magnitude the cavity pressure does not change Thus the final inflow rate becomes Rl + 222 ml/minute, where Rl was the initial inflow rate Thus in the proposed invention the cavity pressure and the outflow rate both can be altered absolutely independent of each other without affecting the value of the other parameter MECHANICAL VERSION OF THE INVENTION:
The mechanical version of the invention shown in figure 3 can be used practically in endoscopic surgenes but it requires a skilled operator having a detailed knowledge of the physical principals involved in cavity distension, which may not be always possible Also the mechanical version has certain practical limitations which shall be explained in the later sections of the manuscnpt This mechanical version of the invention has been discussed only in order to explam more clearly the basic physical principals of the invention
CONTROLLER BASED VERSION OF THE INVENTION:
Referring to figure 2, this figure shows a schematic diagram of the main invention which is proposed to be used m endoscopic procedures. Figure 2 and figure 3 are similar except that m figure 3 the controller system is not included A tachometer, not shown in the diagrams, is coupled to each pump and sends information regarding the pump RPM's to the controller 25 via wires 3 and 17 respectively. The pump flow rates bemg proportional to the pump rotation speed the tachometer signals always conveys flow rate related mformation to the controller The controller also regulates the rotation speed of the two pumps via electncal signals sent through wires 3 and 17. The pressure transducer 14 conveys the fluid pressure signal to the controller via wires 13 The pressure transducer 5 always sends the bladder cavity pressure related information to the controller via wires 12 The controller can be programmed can be programmed not to allow a build up of air pressure which is more than the maximum allowable cavity pressure On the basis of a pressure feed back signal received from the pressure transducer 14 the controller regulates the rotational speed of the inflow pump 1 The outflow pump 20 works at fixed outflow rates and the flow rate of this pump is also regulated by the controller via suitable electncal signals sent via wires 16 A provision exists by which desired values for P and R2 can be fed mto the controller and the values Rl, R2 and P can be continuously displayed via suitable display means incorporated m the controller The pressure reading of the pressure transducer 5 can also be displayed m the controller The controller can be programmed to perform many special functions related to endoscopic surgery which shall be discussed in the following paragraphs
METHOD OF OPERATING THE CONTROLLER BASED VERSION OF THE INVENTION:
Again refemng to figure 2, in context with the present invention at the start of surgery the surgeon initially selects suitable values for cavity pressure P and outflow rate R2 The said desired values of P and R2 are fed into the controller via suitable mput means mcorporated m the controller The diameter D at the constnction site 8 remams fixed at some pre selected value The diameter of the constnction site 8 is so chosen that it suits the operational needs of the endoscopic procedure When the system shown m figure 2 is operated the controller 25 instructs the outflow pump 20 via wires 16 to continuously extract fluid out of the body cavity 15 at a desired fixed outflow rate R2 Thus all through the surgery the outflow rate remains fixed at R2 irrespective of any internal or external factors unless intentionally changed by the surgeon The cavity pressure is sensed by the pressure transducer 14 and a corresponding pressure feedback signal is sent to the controller via wires 13 on the basis of
which the controller regulates the inflow rate Rl, via wires 2 After the system is made operational the controller 25 gradually increases the inflow rate up to the point where the desired preset cavity pressure P is achieved Let the value of the inflow rate at which the desired cavity pressure is achieved be termed as 'Rl Final' It is obvious that the value 'Rl final' is actually determmed by the controller by a pressure feed back mechanism and such determmation of the value 'Rl Final' is based on the preset values of R2 and P The controller is so programmed that once the value 'Rl Fmal' is achieved and is mamtamed for a desired mmimum time interval, for example 10 seconds, after which the controller releases the inflow pump 1 from its pressure feedback control mechanism and allow the mflow pump 1 to operate on its own at an mflow rate 'Rl Final' which was determined by the controller In this manner the two positive displacement pumps continue to work at fixed flow rates to maintain a desired stable cavity pressure. The controller is also programmed that in case the cavity pressure subsequently alters, for example due to intravasation, by a desired minimum preset magnitude and for a desired mmimum time, which may hypothetically be 10 seconds, the inflow pump 1 again comes under the pressure feedback control of the controller and a new value of 'Rl Final' is determined by the controller after which the inflow pump 1 is again allowed to be operated without the pressure feedback mechanism at the newly determined 'Rl Final' inflow rate Such sequence of events contmue to occur throughout the endoscopic procedure Taking an imagmary example if the total surgical time is 60 minutes then It may be hypothetically possible to operate the inflow pump mdependent of the pressure feedback mechanism for 55 minutes and under the control of the pressure feedback mechanism for 5 mmutes However, provision of operating the mflow pump 1 under a pressure feedback mechanism all through the endoscopic procedure can also be incorporated THE ADVANTAGE OF OPERATING THE INFLOW PUMP INDEPENDENT OF THE PRESSURE FEEDBACK MECHANisM:
The only reason for operatmg the mflow pump 1 mdependent of the pressure feedback mechanism is to avoid unnecessary corrections of minor pressure vanations caused by physiological cavity wall contractions and the mechanical movements of the imgation tubes. The concept of physiological cavity wall contractions has been explamed m detail under the heading "basic physics of cavity distension' In the present invention the physiological vanations m cavity pressure are automatically corrected by the constriction site 8 without the need of a controller If the cavity contracts a minute quantity of fluid which is pushed out of the cavity and this causes a correspondmg volume of air to escape vie the constnction site 8 It is to be noted that the distal end of tube 7 is open at atmosphenc pressure thus air escapes
via the constnction site 8 agamst a zero pressure head, which is atmosphenc pressure Thus, the transient, insignificant and instantaneous nse/fall m cavity pressure vanations get stabihzed at the desired preset value within a fraction of seconds. Alternatively if the cavity expands a suitable volume of fluid is sucked into the cavity from the fluid source container 10 and this is accompanied by a corresponding transient decrease in the flow rate at which air is escaping via the constnction site 8 but if the magnitude of the said physiological expansion is more air may even be sucked into the cavity via the constnction site 8. This implies that the constnction site 8 is helpmg m mamtammg a stable cavity pressure despite physiological cavity wall contractions by suitably varymg the magnitude of an imaginary fluid flow vector passing through the constnction site 8 Normally the direction of such imaginary vector is always towards the open distal end of tube 7 while its magnitude constantly vanes to take care of the pressure changes resulting due to physiological cavity confractions Normally a cavity continuously contracts and dilates by approximately the same magnitudes thus there is little logic to check the minor pressure vanations emanating from the said contractions. Also the opening of the constriction site 8 does not allow the said physiological cavity pressure fluctuations to cause any significant cavity wall movement excursions by allowmg to and fro movement of air flow through its lumen However, if the said pressure changes are made to be corrected by a controller, as is done m the prior art systems, the cavity wall may exhibit significant inegular pressure fluctuations which may result m significant movement excursions of the cavity wall, thus disallowing a predictably stable mechanical stabilization of the cavity walls However, in the eventuality of fluid intravasation the fall m cavity pressure drop is relatively more permanent in nature thus needs to be corrected by the controller As explained in the previous paragraph the controller is so programmed that the inflow pump 1 automatically comes under the pressure feedback control mechanism of the controller in case the cavity pressure alters by a desired minimum preset magnitude and for a desired preset time interval, thus a new 'Rl Final' mflow rate is established at which the mflow pump is again allowed to operate without the feedback control of the controller As a safety precaution a provision can be made in the controller via suitable input means to fix an upper safe limit for the inflow rate Rl, the cavity pressure P and the pressure inside the bladder cavity such that these safe limits are not exceeded accidentally
SELECTION OF A SUITABLE DIAMETER FOR THE CONSTRICTION SITE:
The most suitable diameter D for the constriction site 8 can be selected for endoscopic procedure or procedures but such an approach must take mto consideration the operational efficiency needs in context with the cavity pressure fluctuations which might occur due to
the inevitable physiological contraction or expansion of the cavity walls If the diameter of the constnction site 8 is very small then the said transient pressure fluctuation m the cavity pressure would be of a relatively larger magnitude and would last for a relatively longer time interval but the associated resultant movement excursion of the cavity wall would be of a relatively small amplitude. Similarly if the diameter of the constnction site 8 is very large then the said transient cavity pressure fluctuations would be of a relatively smaller magnitude and would last for a relatively shorter time interval but the associated resultant movement excursion of the cavity walls would be of a much larger amplitude These statements are explained by the help of three hypothetical numencal assumptions as stated m table 2 which is as follows Table2
(Table Removed)
(Note. A similar table can be hypothetically constructed taking into consideration cavity wall expansion, instead of contraction.)
In context with routine endoscopic procedures the above mentioned hypothetical situation associated with serial number 2 is most acceptable out of the three hypothetical examples because a high magnitude cavity wall movement excursion is not at all desirable while a moderately high transient pressure surge may be acceptable m most endoscopic procedures Thus the nuisance value of a cavity wall movement excursion is relatively more than the nuisance value of the said transient pressure surge However the amplitude of the pressure surge should also be not very high because it may promote intravasation and other problems Thus while selecting the diameter of the constriction site two things are kept m mind, flie operational needs of the endoscopic procedure and the anticipated cavity wall contraction and expansion movements Thus in those endoscopic procedures where mechanical stability of the cavity walls is important the numencal value of the constnction site diameter D should be relatively smaller There may be endoscopic precedures where mechanical stability of the
cavity walls is not the major concern and in such case a relatively higher value of D may be
chosen
LIMITING AND PREDICTING CAVITY PRESSURE SURGE IN CASE OF
ACCIDENTAL OUTFLOW OBSTRUCTION:
If an abnormally high pressure develops inside a tissue cavity dunng endoscopic surgery it may cause mechanical rupture of the cavity and may also lead to dangerous intravasation Referring to figure 2 if dunng endoscopic surgery the outflow tube is accidentally blocked the cavity pressure does not mcrease to dangerous levels because the controller automatically instructs the pump 1 to work at a reduced RPM, thus a surgical complication is avoided Refemng to the system shown in figure 3 if the outflow tube 18 is accidentally blocked the cavity pressure nses to a dangerously high value in the absence of a controller In context with figure 3 an accidental obstruction of the outflow tube or a deliberate obstruction of the mflow tube as achieved by willfully closing the inflow port, both the situations result in a steeply nsmg pressure as measured by the transducer 14. Thus, while using the mechanical version of the invention as shown m figure 3, it is suggested that before starting the endoscopic surgery the surgeon should deliberately block the distal end of the mflow tube 11 by closing the inflow port of the endoscope and note the resultant maximum pressure nse If the resultant pressure is higher than the maximum prescnbed safe cavity pressure, then the diameter of the constnction site can be increased by some magnitude such that the resultant pressure created by blocking the inflow tube is well below the maximum safe pressure prescnbed for the tissue cavity In this manner, for a mechanical system as shown in figure 3, for a specific inflow rate Rl, the maximum resultant pressure that would develop inside the cavity in the case of a block in the outflow tube can be predictably known and limited Such method of knowmg and limiting the nse in cavity pressure as a result of outflow tube obstruction does not have much role in the controller based version of the invention as shown m figure 2 However, even if the controller based version of the invention as shown in figure 2 is being used and a high out flow rate is bemg used then if the outflow tube is suddenly obstructed a transient pressure surge of a relatively small or large amplitude may be expenenced before the controller finally stabihzes the inflow pump rotation speed at a significantly reduced value to mamtam the initially desired preset cavity pressure Such pressure surge occurs because initially the pressure transducer senses an exponentially increasing cavity pressure, next a corresponding feedback signal is sent to the controller and the controller finally acts by reducing the rotattonal speed of the inflow pump and all these actions may take a few seconds to be implemented, especially if the inflow pump was
operating at a very high speed of rotation, and m this short time mterval a transient surge in the cavity pressure may be expenenced The amplitude of such pressure surge would be small due to the controller feedback mechanism but even a small magnitude surge may damage fragile tissues, for example tissue inside a brain tissue cavity The amplitude of the said surge can be predictably reduced by suitably mcreasing the value D Thus a relatively higher value of D enhances patient safety by predictably limitmg the maximum pressure which can develop inside the cavity m case of an accidental obstruction of the outflow tube 18 if the mechanical version of the invention is being used and it also predictably limits the amplitude of any small amplitude pressure surge which might occur when the inflow tube is accidentally blocked while the controller based version of the invention is being used It has been described in the previous paragraph that the operational efficiency of the system also improves if the value of D is increased Thus a suitable value of D can be selected by keeping into consideration patient safety and system efficiency Once a suitable value for D is selected it never altered thereafter as has already been discussed previously The systems shown in figures 2 and 3 can also have the provision of mcorporating constnction sites having different diameters D to suit and accommodate the operational needs of multiple type of endoscopic procedures
METHODS OF SHORTENING THE CAVITY REFILLING TIME: The advantage of shortenmg the cavity refilling time has already been discussed in a preceding paragraph and in the present invention this beneficial maneuver can be carried out by the help of the controller Refemng to figure 2, one simple way of reducing the cavity refilling time is by temporanly increasing the fluid flow rate into the cavity while the cavity is being filled The physical pnncipals related to the said maneuver shall now be descnbed Refemng to figure 2 let the difference in the values of Rl and R2 be denoted by a value R which can be stated in equation form as R = R1-R2. Also Rl has to be always more than R2 if any positive cavity pressure is to be maintained In the system shown in figure 2 it is seen that if the cavity pressure is fixed at a preset value P then the value R = R1-R2 also never changes irrespective of the desired outflow rate The value D is always fixed as already discussed This implies that m the normal operational mode, for any fixed value of P, the value R = R1-R2 always remains the same However, when the inflow port is deliberately closed the pressure transducer 14 senses an increased pressure due to which the mflow rate is significantly reduced by the pressure feedback circuit, the outflow rate being always fixed at a value R2 In a mathematical manner it can be stated that if the inflow port is deliberately
closed the value R reduces while the pressure value P remains unchanged A reduction m
the value R of a certain minimum minimum magnitude associated with an unchanged P can
serve as a tngger which prompts the controller to carry out a specified sequence of events
Let such tngger be termed as 'refilling initiation trigger' The controller can be so
programmed such that upon being prompted by the 'refilling initiation tngger' the controller
can carry out any one of the below mentioned three maneuvers A, B or C
1 Maneuver A The moment the controller is prompted by a 'refilling initiation tngger'
the controller makes the pump 5 to work at some increased flow rate such that a pressure PI, which usually would be higher than the desired cavity pressure, is created and maintamed in the fluid source contamer 10 The value of PI is so selected that when the inflow port is opened after reintroducing the endoscope the cavity gets completely filled up m a desired shorter time interval and at the end of such a maneuver the cavity pressure also should not exceed a prescribed maximum safe cavity pressure or a lower value as desired by the surgeon. Subsequent to opening the inflow port the pressunzed fluid accumulated m the inflow circuit enters the cavity m the form of a transient high velocity jet lasting for a few seconds, due to which the cavity gets filled at an accelerated pace thus reducing the total refilling time The cavity refilling time can thus be reduced by programming the controller to create and maintain a suitable higher value of PI but it is also important that the value PI should be low enough such ttiat at the end of the refilling phase, that is when the cavity is completely filled, the pressure mside the cavity does not exceed the maximum prescnbed safe cavity pressure The moment the inflow port is opened the pressunzed fluid enters into the cavity and pressure transducer 14 immediately senses a fall m pressure below PI The controller has to be further programmed that such that any fiirther fall m pressure below PI should serve as a second tngger which prompts the controller to start workmg in the normal mode By normal mode it is meant that the controller functions in order to maintain a desired cavity pressure at a desired outflow rate as was initially decided at the beginning of the surgery The only draw back in this proposed method of reducing the cavity refilling time is that an accidental kinking of the outflow tube 18 may be wrongly sensed by the controller as deliberately blockmg the inflow port But such accident can be avoided by fixing a suitable upper limit for the cavity pressure or to just accept the remote possibility of such a remote accident but the maximum cavity pressure created m such an eventuality is known
and can also be limited Some hypothetical numencal examples shall be taken in order
to further clanfy the steps proposed in this paragraph It is practically seen m
hysteroscopy that if the value PI is taken as 160 mm Hg a utenne cavity having a
volume capacity about 20 ml gets filled m approximately 2 seconds and at the end of
which a utenne cavity pressure of 60 mm Hg is created If the cavity had been
allowed to fill at a normal flow rate used in actual surgery, for example 50 ml/minute,
it would have taken 24 seconds to completely fill a cavity havmg the same volume
capacity However if a bladder cavity having a large volume capacity of up to 300 ml
is substituted in place of the utenne cavity the proposed 'method A' cannot be used
for reducing the cavity refilling time Methods B and C are being proposed to reduce
the cavity refilling in the case of large cavities like bladder cavity
2 Method B Let us take a hypothetical example of a bladder cavity having volume
capacity of 300 ml and the desired cavity pressure while domg the endoscopic surgery bemg 30 mm Hg As explained in method A the controller is programmed to create a pressure PI when the inflow tube is deliberately blocked after withdrawmg the endoscope In method A the openmg of the inflow port after again mtroducmg tfie endoscope into the cavity, serves as the second tngger for the controller to start workmg m the normal operational mode to mamtain a desired cavity pressure and at a specified outflow rate but in method B the controller is programmed differently such that opening the of inflow port after again introducing the endoscope into the cavity should serve as the second tngger which prompts the controller to work at an increased flow rate for a specified time, such time being the calculated time mterval in which the cavity would get completely filled, and after the expiry of such specified time the controller bemg further programmed to start workmg the system in the normal operational mode. Taking an hypothetical example with numerical values, if the value PI was taken as 160 mm Hg, as was assumed in method A, then 20 ml fluid shall accumulate inside the bladder cavity m 2 seconds but still 280 ml = 300 ml - 20 ml more fluid needs to be introduced inside the bladder cavity in order to fill it completely Hypothetically, the controller may be so programmed that opening of the inflow port should serve as a second tngger to the controller to make the inflow pump 5 work at an inflow rate of 1000 ml/minute for 16 8 seconds At such flow rate 280 ml fluid can be pushed into the bladder cavity withm 16 8 seconds Had the bladder cavity been filled at an mflow rate of 50 ml/mm it would have taken 6 mmutes for the
cavity to get completely filled where as by resorting to method B the cavity filling
time is reduced to 188 = 2 + 168 seconds
3 Method C Let the 'refiUmg initiation tngger' serve only as a tngger which informs
the controller that the inflow port has been deliberately blocked and the controller should be so programmed that it allows the mflow pump to continue workmg in the normal operational mode, that is to maintain the desired cavity pressure. The openmg of the mflow port can serve as the second tngger which prompts the controller to make the inflow pump work at an increased flow rate for a specified time and then to again start working m the normal operational mode This would reduce the cavity refiUmg time significantly Taking a hypothetical example similar to the example taken m method B, if opening the inflow port serves as a tngger to make the inflow pump work at a flow rate of 1000 ml/mm for 18 seconds then the bladder cavity would get completely filled in 18 seconds It is to be noted that m this paragraph the term 'inflow rate' is not the rate which fluid enters mto the cavity via the mflow tube 11 but it is the flow rate of pump 1
MEASUREMENT OF THE ACTUAL CAVITY PRESSURE:
In the system shown in figures 1, 2, 3 and 4 the value P refers to the actual fluid pressure mside the cavity 15, but m reality P is a pressure value which is sensed by the transducer 14 in the mflow tube, such as at a point 26 which is situated m the upstream part of the inflow tube 11, far away from the cavity In any system the most convenient place for mstallmg the pressure transducer is inside the mam pump housing As already discussed a transducer located in such position may not measure the actual pressure inside the cavity In the out flow rate ranging between 0 to 500 ml/min such pressure difference is m the range between 0 to 2 mm Hg approximately and the said pressure difference remains constant all through surgery at any fixed outflow rate Thus in the proposed invention the pressure P measured by the transducer 14, being only negligibly higher than the actual cavity pressure, may be considered to represent the actual cavity pressure
AVOID CHANGING THE FLUID SOURCE RESERVOIR CONTAINER: The collapsible fluid source reservoir 10 can contam only a limited quantity of ungating fluid usually ranging between 500 ml to 2 5 liters Dunng an endoscopic procedure when the imgation fluid contained inside the reservoir 10 is consumed then the same is replenished by removing the empty container 10 and replacing it with a fresh container 10 which is full of the imgation fluid Such maneuver wastes valuable surgical time In figure 4 a fluid supply tube 27 contaming a fluid flow control valve 28 has been proposed In case the fluid source
container 10 empties dunng an endoscopic procedure the imgation fluid can be mstiUed at a suitably fast rate via the said tube 27 by fully opening the valve 28 and simultaneously fully closmg the valve 29, shown in figure 4, and also simultaneously making the value of the mflow rate Rl equal to zero or a negative value. The said fluid control valves 28 and 29 may also be clamps which are applied externally over tubes 27 and 11 to completely block or open the lumen of the said tubes In order to aid the said imgation fluid replenishing maneuver the diameter D of the constnction site 8 can be temporanly increased to the maximum possible value or a suitable controlled air releasing vent may be incorporated in the air supply tube 4 or m the pump itself Further the controlled may be programmed to control the valves 28 and 29, the said air release vent and pump 1 For example the controller may be so programmed that when the imgation fluid is being replenished via tube 27, then by a single command the valve 28 is fiiUy opened, valve 29 is fully closed, an air release vent attached to tube 4 is fiilly opens and the pump 1 temporanly stops Alternatively a fluid supply tube such as tube 33 having a fluid flow control valve 33 may be directly connected to the fluid source reservoir 10 as shown m figure 4 The fluid supply tube 33 has been depicted by depicted by two dashed parallel Imes The advantage of incorporating tube 33 is that this tube can have a have a relatively large mner diameter which would promote a more rapid filling of the fluid source container 10 While in context witii tube 27 even if the inner diameter of this tube is increased the rapidity at which the fluid source reservoir 10 could be filled would be limited my the smaller diameter of the inflow tube 11 Also irrigation fluid could continuously be instilled mto the fluid source reservou-10 via tube 33 or 27 at a flow rate 'R Replimsh' by utilizing a positive displacement pump such as a penstaltic pump The value 'R.Replinish' obviously has to be lower than the value R2 However in order to incorporate such concept suitable modifications have to be made, both structural and controller based. After suitable structural modifications such as installation of the second penstaltic pump the controller has to be so programmed that if fluid is instilled into the fluid source reservoir at a rate 'R Replmish' then the inflow rate should automatically reduce to a suitable value, such as (Rl - R Replimsh) It is obvious that the controlled can be programmed in multiple ways in context with the instilling fluid via the tubes 27 and 33 Such provision of instilling fluid via tubes 27 and 33 would avoid interrupting surgery m order to refill the fluid source reservoir 10 A VARIABLE CONSTRICTION SITE
In context with the system shown in figure 1,2, 3 and 4 it is also possible to have a system in which the cavity pressure is maintained and regulated by continuously varying, by the help of a controller, the diameter D at the constriction site 8 The housing tube having the
constriction site is substantially responsible for dampening the pressure pulsation or minimizing the turbulence inside the cavity It however may not provide any substantial dampening to the pressure pulsation caused by the working of the inflow or outflow pumps The diameter D at the constriction site 8 could also be intermittently regulated by a controller as and when required for example in the eventuality of fluid intravasation or extravasation thus implying that the diameter D shall be free from the influence of the controller for most of the time and shall be brought under the influence of the controller only when needed and that also for only a small part of the total surgical time Such a concept has been descnbed m great detail m the previous paragraphs in context with figure 2 In the 'vanable constnction' system proposed in this paragraph both pumps 1 and 20 would always operate at desired but fixed flow rates and the cavity pressure would be regulated only by varying the diameter D at the constnction site 8 At the start of the surgery the inflow and outflow rates would be set by feeding suitable flow rate values into the controller after which the controller would not influence or regulate the said two pumps and the cavity pressure would be mamtained only by varying the diameter D at the constnction site 8 In order to vary the diameter at the constnction site 8 a suitable electromechanical devise such as a solenoid operated devise could be installed over the housing tube 7 Such a devise is not a devise which would either totally close or totally open the lumen of the pipe By the help of the said devise the lumen diameter would be vaned in a controlled manner and not just by totally opening or totally closing the lumen The said devise could compnse of a long coil containing a movable long cylmdncal magnet and this magnet piece by pressing over the tube, would vary the mner diameter of the tube When current passes through such coil the magnet piece would either be pulled in or pushed out dependmg upon the direction of the current and the polanty of the magnet and the force which the said long cylmdncal magnet piece could apply over the plastic tube would depend upon the current density passing through the coil or m simpler terms the amount of electncal energy supplied to the coil In context with the present paragraph the controller shall regulated the amount of electncal energy supplied to the coil such that the magnetic rod presses over the tube with an adequate force and the inner diameter of the pipe would depend upon such force Thus the inner diameter of the tube shall be a function of the current density. The system efficiency of this particular embodiment of the proposed invention could be greatly enhanced by incorporatmg a system of pump synchronization as descnbed in the next paragraph However the said solenoid system for the constnction site has not been incorporated in any of the figures only to keep the drawings simple
A METHOD TO DAMPEN THE PRESSURE PULSATIONS CAUSED BY THE OUTFLOW POSITIVE DisPLACEMENT PUMP
Referring to figure 2 the outflow positive displacement pump, that is the outflow penstaltic pump 20 creates pressure pulsations which are invariably transmitted to tissue cavity leading an undesirable turbulence mside the tissue cavity The fluid pressure is pulsatile in nature because the penstaltic pump 20 constantly extracts fluid from the tissue cavity via the outflow tube 18 in a pulsed manner and not in a continuous manner and this leads to fluid pressure pulsations The said pulsations are transmitted to the tissue cavity 15 in a retrograde manner via the outflow tube 18 Hypothetically assuming that the pump 20 rotates at fixed RPM then in that case the frequency of such pulsations would remam uniformly the same all through the operation of the pump If a graph is plotted for the said pulsations, by relatmg the fluid pressure to the 'Y' axis and the time to the 'X' axis, then such graph would have a uniform shape having positive and negative pressure swmgs of a predictably fixed amplitude and fixed frequency It is to be noted that as the pump RPM is increased the frequency as well as the amplitude of the said pressure swings also increase The said pulsations are produced because each time any one roller of the penstaltic pump comes in apposition with a fixed point, for example the inlet end of the peristaltic pump 20, some fluid is withdrawn from the outflow tube 18 by the outflow penstaltic pump via its inlet end in the form of a bolus The wave form of such pulsations need not be sinusoidal, but for the sake of an easier understanding let the said waveform be hypothetically assumed to be sinusoidal m nature As already stated, if the pump RPM increases then along with the frequency the amplitude of the said waveform also increases When the pump 20 rotates m the direction of the curved arrow fluid is extracted from the outflow tube 18, the cavity 15 and the mflow tube 11 and let all three of these collectively be termed as 'fluid extraction region'. In physical terms the said pressure pulsations are produced because the fluid tends to be extracted from the 'fluid extraction region' in the form of regular pulses wherem each pulse corresponds to a fixed volume of fluid pulled by a roller from the 'fluid extraction region' m the form of a bolus of fluid Thus the motion of each roller would correspond to one complete sinusoidal pressure wave Thus the motion of each roller would correspond to one complete sinusoidal pressure wave, assuming that the said waveform has been assumed to be sinusoidal as previously stated The movement of a single roller in relation to a fixed point such as the mlet end of the pump can be hypothetically divided into three parts, that is, part one when the roller approaches the said point, part 2 when the roller is in apposition with the said point and part 3 when the roller moves away from the said point Let the parts 1, 2 and 3 be collectively
termed as 'single roller movement' and the time taken to accomplish the said 'smgle roller movement' be termed as 'single roller time' Assummg the pressure waveform to be a sinusoidal curve, each 'single roller movement' corresponds to one complete sinusoidal pressure waveform consisting of a positive pressure pulse followed by a negative pressure pulse or vice versa Also the time period of flie assumed sinusoidal wave form would be equal to 'single roller time' If dunng a negative pressure pulse an adequate volume of fluid is removed from the 'fluid extraction region' and dunng a positive pressure pulse the same adequate volume of fluid is again added back into the 'fluid extraction region' the smusoidal nature of the pressure waveform could get dampened and the resultant waveform would get transformed into an almost straight line curve The resultant waveform could theoretically be an absolute straight Ime if the wave form associated with the said process of adding and removing adequate volumes of fluid from the 'fluid extraction region' absolutely resembled with the wave produced as a result of the pulsatile flow of the peristaltic pump and the phase difference between the two waves was exactly 180 degrees however this may not be achieved m practical situations However a substantial dampening of the resultant waveform could be practically achieved if a synnge system was synchronously coupled with the outflow penstaltic pump 20 and the smgle outlet end of the said synnge system was connected with the 'fluid extraction region'
The said synnge system is shown m figure 7 The synnge system 42 consists of a piston 38 denoted by a shaded area and the piston 38 moves up and down inside a cylinder 42 while making a watertight contact with the iimer walls of this cylmder 42. One end of a straight rod 41 is connected to the piston while the other end of this rod 41 is connected to a couplmg mechanism 36 housed on a common rotatmg shaft 35 The couplmg mechanism 36 and the penstaltic pump 20, both are attached on this common shaft 35 The coupling mechanism 36 is so designed tiiat it converts the rotary motion of the shaft 35 into a Imear up down motion of rod 41 which is ultimately manifested as an up down movement of piston 38 inside the cylinder 42 The up down motion of the rod 41 is denoted by arrows 38 and 40 Thus the shaft 35 is a common shaft which mechanically operates both, pump 20 as well as the synnge system 42 The direction of rotation of the shaft 35 is denoted by a curved arrow located at the right end of the shaft 35 The synnge system 42, as the name suggests, resembles a hypodermic synnge used for givmg mjections to patients Obviously, the sjoinge system 42 has only one single opening 43 A tube 44 extending between the openmg 43 and the outflow tube 18 connects the synnge system to the outflow tube 18 Tube 18 is a part of the said 'fluid extraction region' descnbed m the previous paragraph Thus the syringe system can be
considered to be connected with the said 'fluid extraction region' The opening 43 can be referred to as an 'outlet end' or an 'inlet end' because the synnge system can push as well as pull fluid from the 'fluid extracton region' However for the sake of convenience henceforth the opening 32 shall be termed as the outlet end of the synnge system 42. The couplmg mechanism 36 is so designed that the vertical movements of the synnge system can be accurately synchronized with the rotary motion of the penstaltic pump 20 The piston 38 can move up>down>up or down>up>down, depending upon the mitial position of the piston at the start of the motion and let each such movement of the piston be termed as a 'complete piston movement' The couplmg mechanism 36 is so designed that while the penstaltic pump 20 rotates by 360 degrees the synnge system correspondingly exhibits 'complete piston movements' which are equal to the number of the rollers of the penstaltic pump Thus for a penstaltic pump which has three rollers then for each 360 degrees rotation of the penstaltic pump the syrmge system exhibits three 'complete piston movements' while for a penstaltic pump with four rollers four 'complete piston movements' would occur for each 360 degree rotation of the penstaltic pump The syrmge system is synchronized with the penstaltic pump via the coupling mechanism 36 in such manner that while a roller of the penstaltic pump produces a negative pressure pulse the synnge system pushes fluid mto the 'fluid accumulation region' and while the same roller produces a positive pressure pulse the synnge system pulls out an equivalent volume of fluid from the 'fluid accumulation region' In order to dampen the pulsations of the penstaltic pump, besides mechanically synchronizing the syringe system with the penstaltic pump, the volume of fluid pulled in or pushed out of the syringe system corresponding to each upward or downward movement of the piston also has to be accurately adjusted, and the same may be done manually by a 'hit and try method' The volume of fluid pulled m or pushed out by the synnge system depends upon the linear movement excursion of the piston 38 Also the magnitude of the downward piston excursion is equal to the magnitude of the upward piston excursion, thus the volume of fluid pushed out is always equal to the volume of fluid pulled in dunng each downward or upward movement Thus the coupling mechanism 36 has two ftinctions, synchronization of the synnge system with the penstaltic pump and adjusting the volume of fluid pulled m or pushed out by the synnge system for each upward or downward movement of the piston The synchronization and the determmation of the said volume to be pushed out or pulled into the synnge system are done manually such that a substantial dampenmg of the pressure pulsations is achieved and once this is achieved the sjTichronization at the level of the coupling 36 is never again disturbed and the volume of fluid pulled m or pushed out of the synnge system for each
movement excursion is also not changed thereafter After the coupling 36 is adjusted with respect to synchronization and the volume of fluid to be pulled in and pushed out, the penstaltic pump pulsations shall contmue to remain dampened independent of the penstaltic pump RPM and the nature of rotation, that is fixed or vanable RPM In simpler terms the penstaltic pump pulsations would contmue to remain dampened even at a high pump RPM Also the pomt at which the synnge system 42 is connected to the said 'fluid extraction region', for example the outflow tube 18, then the position of such a point should also not be changed thereafter because this may bring about a phase difference between the waveform related to the peristaltic pump pulsations and the waveform related to the synnge system pulsations, thus the resultant dampening could no longer be satisfactory Also preferably the outlet tube 44 of the synnge system should be connected as close to the outlet end of the inflow penstaltic pump as possible
The coupling 36 can be compared to some extent with the conventional CAM system present in automobile engines Any specific mechanical design for the coupling 36 is not important, it is the resultant fiinction of the couplmg 36 with respect to the piston movement, as already descnbed, which is important The coupling27 can have many mechanical designs Figure 5 shows one such possible mechanical design for the coupling 36 In figure 5 a small length of the common shaft 35, which is related to the coupling 36, has been made of tnangular shape as seen in its cross sectional view and the same is labeled as 46 Let this tnangular part 46 be termed as the 'piston coupler' The edges of the piston coupler are shown sharp however they could preferably be rounded to suit vanous operational needs Similarly the size of the 'piston coupler' could also be increased or decreased in order to decrease or increase the volume of fluid displaced by the cylmder dunng a downward or upward movement of the piston The central axis pomt of the 'piston coupler' is denoted by pomt 47. In case the dimensions of the 'piston coupler' are chosen to be relatively larger than the dimension of the common shaft 35, the point 47 could also represent the pomt at which the common shaft 35 passes through the 'piston coupler' and in such a situation the 'piston coupler' 46 could be manually rotated on the common shaft 35 m a clockwise or anti clockwise direction and then locked mechanically at a position which provides the most accurate synchronization The sprmgs 48 and 49 extending between the inner walls of the cylinder and the piston exert a constant and substantially large upward pull on the piston 38 which causes the rod 41 to constantly be m apposition with the 'piston coupler' 46 The spnngs can be one or more than one in number and the spnngs can also be substituted by any other mechanical means also which provide an active upward movement of the piston The 'piston coupler' 46 is assumed to be able to apply
a substantially large downward force on the piston 38 via rod 41 such that a correspondmg transient negative fluid pressure inside the cylinder can be totally neglected m the face of the said large substantial downward force Similarly the spnngs 48 and 49 are capable of pullmg up the piston with a substantially large force such that a corresponding transient positive fluid pressure pulse inside the cylinder could be totally neglected. The idea is that the downward movement of the piston should not be aided by the negative pressure pulse inside the cylmder, this downward movement should be an active movement for which energy is to be denved from the spnngs from the shaft 35 Similarly the upward movement of the piston should not be aided by the positive pressure pulse mside the cylinder, this upward movement should be an active movement for which energy is to be denved from the spnngs 48 and 49 The energy for the said upward movement of the piston could also be denved from the shaft 35 if suitable mechanical provision facilitating an active upward movement of the piston could be provided at the level of the coupling 46
It is important to note that it is not mandatory to use the said 'pressure pulse dampening system' with a penstaltic pump only as, with suitable mechanical modifications, the 'pressure pulse dampenmg system' could be used beneficially with any type of a positve displacement pump
The 'pressure pulse dampening system' could also be a mechanism like the 'piston coupler' 46 shown in figure 5 whose rounded edges could directly impinge on a suitable area situated on the outer surface of the 'fluid extraction region' in a uniform synchronized manner, as descnbed, such that this results in contmuous uniform synchronized vanations m the total volume capacity of 'fluid extraction region' The said suitable area on the outer surface of the 'fluid extraction region' could be a membrane made consisting of a strong resilient polymenc matenal having an adequate elasticity The said membrane should also be sufficiently thick and should have an adequate elasticity such that an outward movement of such membrane, a movement related to the upward pull by the said spnngs, applied a substantially larger force m companson to force related with the transient correspondmg pressure pulse A METHOD TO DAMPEN THE PRESSURE PULSATIONS CAUSED BY THE INFLOW POSITIVE DisPLACEMENT PUMP
A pressure dampening system similar to the one suggested for the outflow side can also be installed on the inflow side as shown in figure 6 and the same has been numbered as 50 A common shaft 59 dnves both the piston pump 1 and the synnge system via coupling 56 which moves the piston 51 via rod 55 and thus the cylinder moves up and down inside cylmder 52 The outlet end 57 of the syrmge system 52 is connected to the air delivery tube 4
via tube 58 The synnge system 52 helps in dampening the air pressure pulsations created by the piston pump I in a similar manner as the synnge system 37 helps in dampening the fluid pressure pulse created by the out flow penstaltic pump 20. The air pressure pulsations from the bladder cavity are ultimately transmitted to the tissue cavity via the inflow tube 11 thus leading to undesirable turbulence inside the tissue cavity. Thus it is important to dampen the air pressure pulsations
The Inventors would like to mention that the pressure dampenmg mechanism descnbed in the present invention is an active pressure dampening system and not a passive dampening system The Applicants have realized that only active pressure dampenmg systems as discussed above provide substantial dampening to the pressure pulsation caused by the penstaltic pumps and relymg on passive factors such as the inherent resistance to the flow of the liquid etc do not provide any effective pressure dampenmg Further, the pressure dampenmg system may not provide any substantial dampenmg to the pressure pulsation caused by the physiological contractions of the cavity walls SYNCHRONIZATION OF THE INFLO AND THE OUTFLOW PUMPS The inflow pump I and the out flow pump 20 are both positive displacement pumps and both these pumps could also be housed on a smgle common dnving shaft in a manner that both pumps were synchronized By synchronization here means that when the inflow pump produces a positive pressure pulse inside the tissue cavity the outflow pump should produce a negative pressure pulse in the cavity. Such synchronization could be achieved by hit and tnal empincal means by adjustmg the spatial onentation of a piston, related to the inflow pump, with a conespondmg penstaltic pump roller in such a manner that the amplitude of the resultant pressure pulse waveform inside the cavity could be made as less as possible However such a system of synchronization on a common central shaft is not practically easy Further m such a system if the pressure needs to be vaned then the same could be possible only by varying the diameter D of the constriction site 8. Also m such a system the inflow and the out flow pumps cannot be run mdependently of each other Thus in such a system it would be mandatory to have a vanable dynamic constriction site preferably under the control in a manner as descnbed m tins manuscnpt
A SYSTEM OF INCORPORATING MULTIPLE PERisTALTIC PUMP TUBES In the preceding parts of the manuscnpt the penstaltic pump 20 is shown to have one single tube 19 which come in contact with the rollers of the penstaltic pumps Arbitranly refemng to the outflow pump 20,

(Equation Removed)

where Rl = Flow rate of pump 20, B = inner diameter of the
penstaltic pump tube 4, L = length of tube 4 and RPM = revolution per minute of pump 5 If
the value B is doubled then for the same RPM the flow rate Rl doubles Similarly if L
doubles then also for RPM the flow rate Rl doubles However keeping in mind the
mechanical constraints the values B and L cannot exceed a certain practical value. However
if two tubes like tube 19 are used in parallel in the pump 20 then the mathematical expression
for the flow rate could be wntten as follows

(Equation Removed)
This implies that if two penstaltic pump tubes are used instead of one single tube then the
flow rate becomes double for the same RPM and if three tubes are used then the flow rate
becomes three times and so on. The frequency of the 'pressure pulsations' created by a
penstaltic pump is directly proportional to the pump RPM The said 'pressure pulsations' are
undesirable thus it is helpful to keep their frequency as minimal as possible if the flow rate is
not compromised Thus this system of mcorporating two or more penstaltic pump tubes helps
m attaining a higher flow rate for a relatively lesser RPM It is but obvious that the said two
or more than two parallel tubes are connected to each other at the inlet and the outlet ends of
the penstaltic pump
DETERMINATION OF THE INSTANTANEOUS REAL TIME RATE OF FLUID
INTRAVASATION
Fluid intravasation is a process by which the imgation fluid enters into the patient's body
system and if excess volume of fluid is intravasated it can be dangerous to the patient's life.
Thus, keeping m mind surgical safety, it is extremely important to constantly know the rate at
which such intravasation occurs so that corrective surgical measures can be taken before a
dangerous volume of fluid intravasates The mventors propose that one fluid flow rate sensor
each be incorporated m the inflow tube and the outflow tube Refemng to figure 1 the inflow
flow rate sensor should be located in the inflow tube 11 anjrwhere between the inlet port of
the endoscope and the outlet end of the fluid source reservoir 10 Such a flow rate sensor
would measure the rate at which fluid enters into the tissue cavity 15 and the same is being
termed as 'cavity inflow rate' Obviously the 'cavity mflow rate' is ttie true mflow rate for
the tissue cavity Similarly the outflow flow rate sensor should be located anywhere m the out
flow tube between the outflow port of the endoscope and the inlet end of the outflow
penstaltic pump 14 or any other outflow positive displacement pump However if an
additional or optional constnction site housing tube 31 is also connected to the out flow tube
18 as shown m figure 4 then the outflow flow rate sensor should be located between the outflow port of the endoscope and the pomt at which the proximal end of the constnction site housing tube 31 is connected to the outflow tube 18 The outflow flow rate sensor measures the rate at which fluid is extracted from the tissue cavity which is the same as R2 that is the flow rate of the outflow pump Now the real time rate of fluid mtravasation, being termed as R3, can be determining by subtracting R2 from the 'cavity inflow rate', the mathematical expression for the same being can be written as R3 = Cavity inflow rate - R2 The said flow rate sensors should be accurate, reliable, easy to install and should not have any movable parts The inventors suggest that a the said sensor compnse of a heating coil m physical contact with a metal plate for heating the same and a temperature sensor placed in contact with the metal plate, the temperature of the metal plate being a function of the fluid flow rate The said flow rate sensors are electncally connected with a micro-controller which automatically subtracts R2 from the 'cavity mflow rate' to give the value R3 The value R3 can also be further integrated with respect to time to give the total volume of fluid intravasated over a certain time interval The said temperature related flow rate sensor could be a 'hot wire anemometer'
DETERMINATION OF THE REAL TIME RATE OF FLUID INTRAVASATION WITHOUT USING FLUID FLOW RATE SENSORS
The tissue cavity pressure P is a function of the RPM of the inflow piston pump (Rl), the cavity outflow rate (R2) and the real time rate of mtravasation (R3) The value P increases as the value RPM of the inflow pump increases and decreases as R3 and R2 increase Thus a mathematical expression could be denved which contains P, RPM of the inflow positive displacement pump, R2 and R3 Such a mathematical expression could be fed into a controller and in this manner the value R3, the real time rate of fluid mtravasation could be determined
The proposed mvention can also be used to impart endoscopic training skills by the help of endoscopic expenmental models based on the present invention. Also use and scope of the present invention is not limited to human tissue cavities and it may be used for performmg multiple endoscopic procedures in animal tissue cavities also and also for imparting training m endoscopic surgenes related to animal tissue cavities
It is believed that the foregomg descnption conveys the best understanding of the objects and the advantages of the present invention It will be understood by those skilled m the art that numerous improvements and modifications may be made to the embodiments of the
mvention disclosed herein without departmg from the departing from the spmt and scope thereof
The proposed invention has obvious use in hysteroscopic surgery, arthroscopic surgery and TURP surgery The proposed invention can also be utilized for carrying out endoscopic procedures in the brain and the spine Brain endoscopic surgery also known as neuro endoscopy is a frequently performed life saving procedure. The human brain has got cavities known as the brain ventricles Many endoscopic procedures are performed by inserting the endoscope into the brain ventricles and many such procedures utilize continuous flow irrigation Endoscopic surgery of the spine is also a frequently performed and many endoscopic procedures related to the spine utilize continuous flow imgation The proposed invention can be useful in other endoscopic procedures also which require continuous flow imgation The present invention can be usefiil in certain non endoscopic procedures also where a tissue cavity needs to be distended by continuous flow imgation such as gall stone dissolution, balloon thermal ablation of the endometnum, phako emulsification procedure related to the eye ball cavity and vitrectomy procedure related to the eye ball cavity The advantage of predicting the required volume for the irrigation fluid at the beginning of the surgery has akeady been explained Such maneuver though extremely simple is extremely helpful In the present invention the outflow rate remains fixed all through the surgery unless intentionally changed by the surgeon The average total surgical time for similar endoscopic procedures usually does no vary and the surgeons on the basic of their past expenence always have an idea of the approximate time which an endoscopic procedure takes Such time multiplied by the chosen outflow rate R2 gives a fairly accurate idea of the total volume of imgation which would be consumed in the proposed endoscopic procedure if intravasation was to be ignored and the surgeons again by their past expenence also have a fairly rough idea of the of the volume of fluid which is intravasated in a certain duration of time for specific endoscopic procedures In this manner the total fluid that would be required in a particular endoscopic procedure can be roughly evaluated but even such rough evaluation is helpftil as explained in a previous paragraph entitled 'Predicting the total volume of required imgation fluid' It is advisable to take a slightly greater volume than that predicted by the method descnbed in this paragraph
The proposed invention can also be used to impart endoscopic training skills by the help of endoscopic expenmental models based on the present invention Also use and scope of the present invention is not limited to human tissue cavities and it may be used for performing
multiple endoscopic procedures in animal tissue cavities also and also for imparting trammg
m endoscopic surgenes related to animal tissue cavities
It is believed that the foregoing descnption conveys the best understanding of the objects and
the advantages of the present invention It will be understood by those skilled in the art that
numerous improvements and modifications may be made to the embodiments of the
invention disclosed herein without departing from the departing from the spint and scope
thereof
THE INVENTION is UNIQUE
There is no other pnor art system in which two positive displacement pumps running
simultaneously at fixed RPM's predictably create and maintain any desired fixed pressure
inside a tissue cavity, despite unpredictable irregular physiological contractions of the cavity
walls, for any precise and fixed outflow rate for unlimited time Also the concept of 'pressure
pulse dampening system', 'pump synchronization' and using more than one peristaltic pump
tubes as discussed in the previous paragraph has not been descnbed m any pnor art system
Besides these unique features the invention has many other unique features also as already
discussed in the previous paragraphs
THE HEART AND SOUL OF THE INVENTION
The constnction site 8 as descnbed in the manuscnpt is the heart and soul of the invention
without which the invention cannot exist
ADVANTAGES OF THE PROPOSED INVENTION
The proposed invention makes endoscopic procedures extremely safe, simple, more accurate
and easy to perform The proposed invention helps the surgeons to perform endoscopic
surgenes with greater safety and confidence especially in the initial phase of their leammg
curve Also a distending system based on the proposed invention can be used in multiple
endoscopic procedures thus reducing the financial burden on the hospital and the patient The
advantages of proposed invention are summanzed in the following table 3 along with the
corresponding disadvantages of the pnor art systems
Table 3
(Table Removed)

CONCLUSION
The proposed invention is novel and unique The invention relates not only to increasing surgical efficiency in certain endoscopic procedures but it also helps in preventing human morbidity and human mortality in many endoscopic procedures Thus the proposed invention is extremely useful for entire mankind.

We Claims :-
1. A system for distending body tissue cavities of subjects by continuous flow irrigation
during endoscopic procedures the said system comprising:
a collapsible fluid source reservoir containing a non viscous physiologic fluid meant
for tissue cavity distension;
said fluid source reservoir being encircled by a bladder cavity, said bladder cavity
being connected to an inflow positive displacement pump through an air transporting
tube for inflating the same and a pressure transducer being coupled to the air
transporting tube;
a fluid supply inflow tube connecting the fluid source reservoir to an inflow port of an
endoscope instrument for pumping the fluid at a controlled flow rate into the body
tissue cavity, the flow rate of the said inflow pump being termed as the inflow rate
and the rate at which the fluid from the inflow tube enters into the tissue cavity being
termed as the cavity inflow rate;
an inflow liquid pressure transducer being coupled to the fluid supply conduit tube;
an outflow port of the endoscope being connectable to an inlet end of a variable speed
positive displacement outflow pump through a outflow tube for removing the fluid
from the cavity at a controlled flow rate, the flow rate of the said outflow pump being
termed as the cavity outflow rate,
an outlet end of the outflow pump being connected to a waste fluid collecting
container via a waste fluid carrying tube, and
characterized that a housing tube having a controllable constriction site is being
coupled to the air transporting tube between the positive displacement inflow pump
and the bladder cavity; wherein the housing tube provides a route for any excess air
present in the bladder cavity or being pumped by the positive displacement pump to
escape to the atmosphere, thereby minimizing turbulence inside the body tissue cavity
and maintaining the body tissue cavity pressure at a stable value despite physiological
contractions of the body tissue cavity wall.
2. A system as claimed in claim 1, wherein a proximal end of the fluid supply conduit tube is connected to the fluid source reservoir and a distal end of the tube being connectable to the inflow port of the endoscope instrument.
3. A system as claimed in claim 1, wherein the positive displacement inflow pump is a piston pump.
4. A system as claimed in claim 1, wherein the housing tube is releasably provided between the positive displacement pump and the bladder cavity to enable replacement of the housing tube with yet another housing tube having a different diameter at the constriction site to suit the operational need of the endoscopic procedure.
5. A system as claimed in claim 1, wherein the housing tube is provided with a clamping means at the constriction site to enable the user to vary the diameter of the housing tube at the constriction site to suit the operational needs of endoscopic procedures.
6. A system as claimed in claim 1, wherein the diameter of the housing tube at the constriction site is in the range of 0.001 mm to a maximum value which is less than the overall diameter of the rest of the housing tube.
7. A system as claimed in claim 1, wherein the diameter of the housing tube at the constriction site is in the range of 0.01 to 2.5 mm.
8. A system as claimed in claim 1, wherein the inflow pressure transducer is located sufficiently away from the cavity site, preferably near the outlet end of the inflow pump from the practical point of view, such that the fluid pressure measured by the same is almost equal to the fluid pressure inside the cavity.
9. A system as claimed in claim 1, wherein a proximal end of the outflow tube being connectable to the outlet port of the endoscope instrument and a distal end of the outflow tube is connected to an inlet end of the variable speed positive displacement outflow pump.
10. A system as claimed in claim 1 further comprising an inflow gas pressure transducer connected between the positive displacement pump and the bladder cavity.
11. A system as claimed in claim 1 further comprising an outflow pressure transducer connected between a proximal end of the outflow tube and the inlet end of the variable speed positive displacement outflow pump for measuring the pressure in the outflow tube.
12. A system as claimed in claim 1, wherein the variable speed positive displacement outflow pump is selected from the group comprising peristaltic pump, piston pump, gear pump and diaphragm pump.
13. A system as claimed in claim 12, wherein the variable speed positive displacement outflow pump is a peristaltic pump.
14. A system as claimed in claim 1, wherein the outlet end of the variable speed positive displacement outflow pump is connected to the waste fluid collecting container through a waste fluid carrying tube.
15. A system as claimed in any one of claims 1 to 14 further comprising a microcontroller means electrically coupled to the inflow gas pressure transducer, the inflow liquid pressure transducer, the outflow pressure transducer, the inflow positive displacement pump and the outflow pump for regulating the operation of the inflow and the outflow pumps.
16. A system as claimed in claim 1, wherein the housing tube is provided with an electromechanical device, to enable the micro-controller to vary tiie diameter of the constriction site.
17. A system as claimed in claim 1 further comprising a housing tube having a variable size constriction site being provided between the outflow tube and the waste fluid reservoir.
18. A system as claimed in claim 17, wherein a proximal end of the housing tube is connected to the outflow near the inlet of the outflow pump.
19. A system as claimed in claim 1 further comprising a fluid replenishing tube connected either directly or indirectly to the fluid source reservoir through a replenishment fluid controlling valve for refilling the fluid source reservoir.
20. A system as claimed in claim 18, wherein the fluid replenishing tube is connected directly to the fluid source reservoir or via the fluid supply inflow tube to the fluid source reservoir.
21. A system as claimed in claim 19 and 20, wherein an inflow fluid controlling valve is provided on the inflow tube for preventing the fluid from entering into the tissue cavity during fluid replenishment phase.
22. A system as claimed in claim 1, wherein the fluid supply conduit tube and the outflow tube and the waste fluid carrying tube are flexible, disposable and are made of polymeric material.
23. A system as claimed in claim 1 fiirther comprising a fluid inflow rate sensor connected to the inflow tube.
24. A system as claimed in claim 23, wherein the fluid inflow rate sensor is located in the lumen or wall of the inflow fluid supply conduit tube for measuring the cavity inflow rate.
25. A system as claimed in claim 1 further comprising a fluid outflow rate sensor connected between the proximal end of the outflow tube and the inlet end of the variable speed positive displacement outflow pump for measuring the cavity outflow rate.
26. A system as claimed in claims 23 to 25, wherein the fluid inflow and the outflow rate sensors consist of a heating coil in physical contact with a metal plate for heating the same and a temperature sensor placed in contact with the metal plate for measuring the temperature of the said metal plate, the temperature of the metal plate being a function of the fluid flow rate.
27. A system as claimed in claim 25, wherein the fluid rate flow sensor is a hot wire anemometer.
28. A system as claimed in claims 23 to 26, wherein instantaneous real time rate of fluid intravasation is determined by electrically connecting the inflow and outflow fluid flow rate sensors to a micro-controller.
29. A system as claimed in claim 1 further comprising an inflow pressure variation dampening means provided on the inflow side for dampening the pressure variation inside the body tissue cavity caused by the positive displacement inflow pump.
30. A system as claimed in claim 29, wherein the inflow pressure variation dampening means comprises a single outlet syringe mechanism, the piston of the same being coupled synchronously to the positive displacement inflow pump through a coupling means and the single outlet end of the said syringe mechanism being connected to the air transporting tube.
31. A system as claimed in claim 1 further comprising an outflow pressure variation dampening means provided on the outflow side for dampening the pressure variation inside the body tissue cavity caused by the positive displacement outflow pump.
32. A system as claimed in claim 31, wherein the outflow pressure variation dampening means comprises a single outlet syringe mechanism, the piston of the same being coupled synchronously to the positive displacement outflow pump through a coupling means and the single outlet end of the said syringe mechanism being connected to the outflow tube.
33. A method of distending a body tissue cavity of a subject by continuous flow irrigation
such that minimal or negligible fluid turbulence is present inside the cavity, such that
any desired cavity pressure can be created and maintained for any desired outflow
rate, said method comprising the steps of:
(a) inflating a bladder cavity that encircles a collapsible fluid source reservoir using a positive displacement pump for dispensing a non viscous physiologic fluid meant for cavity distension from the fluid source reservoir to an inflow port of an endoscope instrument at a controlled flow rate through a fluid supply conduit tube;
(b) injecting the non- viscous physiologic fluid at a controlled flow rate into the cavity for distending the body tissue cavity of the subject, the rate at which the fluid enters into the tissue cavity from via the inflow fluid conduit being termed as the cavity inflow rate;
(c) removing a waste fluid from the cavity via the outlet port of the endoscope;
(d) actively extracting the waste fluid via the outlet port of the endoscope and transporting it to a waste fluid collecting reservoir at a confrolled flow rate, the said flow rate being termed as the cavity outflow rate, through a outflow conduit tube, a variable speed positive displacement outflow pump and a waste fluid carrying tube and
(e) providing a housing tube having a controllable constriction site between the bladder cavity and the positive displacement inflow pump such that the housing tube provides a route for any excess air being pumped by the positive displacement pump or due to the physiologic contraction of the body tissue cavity walls escape to the atmosphere, thereby avoiding turbulence inside the body tissue cavity and to maintain a stable pressure inside the body tissue cavity.

34. A system for distending body tissue cavities of subjects by continuous flow irrigation during endoscopic procedures such as herein described with reference to the accompanying drawings.
35. A method of distending a body tissue cavity of a subject by continuous flow irrigation such as herein described with reference to the accompanying drawings.