A LOW TURBULENCE FLUID MANAGEMENT SYSTEM FOR ENDOSCOPIC
PROCEDURES FIELD OF INVENTION
The present invention relates to a system for distending body tissue cavities of subjects
utilizing continuous flow irigation dunng endoscopic procedures The system and the
methods of the present invention descnbed above can be used m any endoscopic
procedure requiring continuous flow imgation few examples of such endoscopic
procedures being hysteroscopic surgery, arthroscopic surgery, trans uretheral surgery
(TURF), endoscopic surgery of the brain and endoscopic surgerv of the spine The
proposed mvention can also have certain useful non medical applications
BACKGROUND OF THE INVENTION
Endoscopic surgery is becoming increasingly 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 pain,
(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 in the corresponding open conventional surgenes a relatively large body part consisting of skin and muscle needs to be cut in order to gain access to an underlying body tissue cavity, in endoscopic surgery instead of cutting body structures like skin and muscle an endoscope is introduced into the body cavity via the natural opening 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 interior 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 'minimal access surgery' Besides reducing the pain associated with surgery, endoscopic surgery also helps in reducing the medical expenses
ENDOSCOPIC SURGERY is PRIMARILY RELATED TO A TisSUE CAVITY: All endoscopic surgeries are carried out on a existing 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 increasing 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 increasing 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 m 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 distending system and no endoscopic procedure should be attempted without a safe distending system because unsafe tissue cavity distending 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 instruments CONTINUOUS FLOW IRRIGATION:
In the present invention, the Inventors are focused on a system for distending body tissue cavities for those endoscopic procedures in which the cavity needs to be distended by utilizing continuous flow imgation only. Here, the term 'continuous flow imgation' means that fluid simultaneously enters and escapes from a tissue cavity via separate entry and exit points, as a resuh 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 m a 'static manner' by simply pushing fluid via a single inflow tube inserted 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 with fluid with the outlet end of the syringe 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 maintained 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 invanably released from the fragile cavity inner lining mix with the distending fluid and endoscopic vision gets clouded within a few seconds or a few minutes Thus continuous flow imgation is needed to constantly wash away blood and tissue debris in 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 imgation systems AN EFFICIENT DisTENDING SYSTEM:
The hiventors 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 maintained in 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 debns in order to allow clear vision Many pnor systems utilize a peristaltic pump over the inflow and or the outflow side and these penstaltic 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 m 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 rises 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 distending 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 in 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) whe-e the authors clearly and exphcitly 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 Imventors would like to provide a brief 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 inflow 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 m the case of a rigid cavity, for example a cavity made of steel
However, the body tissue cavities are not rigid 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 maintain the cavity pressure and cavity distension in a predictably stable fashion
Further, the inflow tube, the out flow tube and the endoscope also invanably move and shake dunng surgery which leads to vanations in fluid flow resistance which is also manifested in the form of variations m the cavity pressure The cavity pressure variations occurring 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 correcting 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 in the imgation circuit BRIEF DESCRIPTION OF AN ENDOSCOPE:
Prior to descnbing the basic layout of a continuous flow imgation system the basic structure of an 'endoscope' needs to be descnbed Endoscope is a cylindncal tube having an outer diameter ranging between 3 to 9 mm approximately A typical endoscope has four charmels 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 in a metal adaptor known as the inflow port while
the distal end of this inflow channel opens near the tip of the endoscope The inflow port is connectable to an inflow tube which carries stenle irrigation fluid from a fluid source reservoir 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 illuminates the walls of the tissue cavity The image thus formed is carried 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 tlirough 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' hi a typical distension system a physiological non viscous liquid like 0 9% normal saline, 1 5% glycine, 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 inflow 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 inflow pump pushes this fluid into the tissue cavity via the said inflow tube The pump operates by consuming certain amount of energy and as a result of this a positive fluid pressure is created inside 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 fi'om 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 in such case the outflow tube directly cames 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 the inflow tube directly supplies the irrigation fluid from a fluid source reservoir to the cavity hi such case the fluid source reservoir is hung at a suitable height above the patient and the said energy for cavity distension is denved from gravity instead of the inflow pump A suitable pressure transducer is attached to the inflow 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 continuous flow imgation system compnses a fluid reservoir bottle hung at a suitable height above the patient and an inflow tube connecting this fluid reservoir to a tissue cavity An out flow tube is incorporated to remove fluid from the tissue cavity In this system there is no pump and no transducer In such a system fluid flows from the fluid source reservoir into the cavity and the required energy is supplied by gravity The pressure developed inside the cavity can be increased or decreased by elevating or lowenng the height of the fluid source reservoir In such system the main limiting factor is the height of the room ceiling beyond which the fluid reservoir cannot be raised This is a crude system having negligible practical importance and has been included only from the academic point of view Also in such a system unlimited volume of irrigation fluid may enter into 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, tyres and a steering 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 oi 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 vanable RPM type which operates at variable RPM during the endoscopic procedure It is extremely important to note that fixed RPM pumps and variable RPM pumps are two separate mechanical entities in 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 inflow 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 du-ectly 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. Relvant references have been included in a PCT application filed by the Inventors in 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 peristaltic pump is used to push irrigation fluid into a tissue cavity. This patent is related to the 'Contmuous Wave n Arthroscopy Pump' marketed by Arthrex. A chamber with volume is connected to the inflow tube and a collapsible bladder is contained within the bladder. The collapsible bladder has an open end connected with tubing to a pressure transducer. Once activated the pump begins to introduce 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 information to a controller which regulates the RPM of the pump on the basis of a pressure feedback mechamsm. Thus by the help of a pressure feedback mechamsm the pressure inside a tissue cavity is maintained by fluctuating around a desired value. In this invention an important purpose of the said chamber is to dampen the pressure pulsations created by the penstaltic pump. Such pressure pulsations create turbulence inside the tissues cavity and are hence undesirable. The method of dampemng the pressure pulsations as descnbed m this 5520638 is not adequately efficient, especially at high pump RPM's. The Inventors would like to submit that the system being claimed in the aforesaid US Patent is a passive dampemng 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 inflow 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 mechamsm the inflow pump is constantly increased or
decreased thereby maintaimng 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.
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
inflow pump is constantly mcreased or decreased thereby maintaimng the cavity aroimd a
desired value. Thus by the help of a pressure feedback mechamsm the pressure inside a
tissue cavity is maintamed by fluctuating around a desired value.
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
continuous flow irrigation.
The main object of the invention is to minimize the amplitude as well as the frequency of
pressure pulsations, inside the tissue cavity, created by the two positive displacement
pumps.
Another object of the present invention is to provide a system for distending tissue
cavities usmg which it being possible to create and maintain 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 distending tissue
cavities usmg 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 distending tissue
cavities using which it being possible to achieve predictably stable mechanical cavity
distension throughout the endoscopic procedure
One more object of the present invention is to provide a system for distending tissue
cavities using which it being possible to predictably maintain 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 distending tissue
cavities using which it being possible to constantly, accurately and reliably determine the
instantaneous real time rate of fluid intravasation into the patient's body by using two
fluid flow rate sensors which do not have any movable components
A further more object of the present invention is to provide a system for distending tissue
cavities using which it being possible to maintain any desired precise and high cavity
pressure without increasing the 'maximum possible fluid intravasation rate'
Another object of the present invention is to provide a system for distending tissue
cavities using which it being possible to measure the actual cavity pressure, in 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 inside the body cavity and the
flow rate of the fluid passing through the body cavity absolutely independent 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 in 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 imgation 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 irrigation fluid which would be required to complete the entire
endoscopic procedure
One another object of the present invention is to provide a system for distending tissue cavities using 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 rise in the cavity pressure in a controlled and predictable manner.
A further object of the present invention is to provide a system for distending tissue cavities using which it being possible to easily, quickly and safely change from one type of irrigation fluid to a different type of imgation fluid, for example between normal saline and glycine, intraoperatively (that is during a surgical procedure), m any desired short period of time such that the cavity pressure does not change during such maneuver. 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 irrigation. The main aim of the invention is to minimize cavity fluid turbulence by minimizing the amplitude as well as the frequency of the pressure pulsations created by two positive displacement pumps. The present invention is a system of creating and maintainmg a desired positive pressure inside 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 creating cavity fluid pressure which is absolutely independent of the cavity outflow rate. The present invention compnses of two peristaltic pumps which work simultaneously, for indefinite time, at fixed flow rates to create and maintam any precise desired cavity pressure for any desired cavity outflow rate, including a zero outflow rate. One pump is located on the inflow side of a cavity while the other pump is attached to the out flow side of the cavity. Further if any fluid is being absorbed into or through the cavity walls, such as fluid infravasation which occurs during hysteroscopic endometrial resection, the mstantaneous real time rate of such fluid absorption can be constantly determined Also the cavity pressure can be mamtamed at any desired high value without increasing the 'maximimi possible fluid mtravasation rate'. In the proposed invention by mcorporatmg a system of pump synchromzation it is possible to reduce fluid turbulence to almost neghgible levels. The proposed invention also has multiple other features of endoscopic surgical relevance which greatly enhance the patient safety and efficiency
during 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 quickly switch dunng endoscopic surgery between two types of irrigation fluids
without varying the cavity pressure and to be able to predict and limit the magnitude of
the maximum increase m 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 main block diagram of the invention along with the 'pressure pulse
dampening system' and the controller
Figure 2 shows the block diagram of the invention without the 'pressure pulse dampening
system'
Figure 3 is similar to figure 2 except that the controller has not been included
Figure 4 shows the inflow part of the system along with the inflow penstaltic pump 5, the
pressure transducer 17 and the constnction site 8
Figure 5 is similar to figure 3 except that m this figure a shaded region represents an area
having an almost similar pressure
Figure 6 is similar to figure 3 except that an optional constnction housing tube 17 and an
optional pressure transducer 63 have been included.
Figure 7 shows is the schematic diagram for pump synchronization on a common rotor
shaft
Figure 8 shows the basic lay out of the 'pressure pulse dampening system'
Figure 9 shows a detailed layout of the synnge mechanism along with a coupling means
DETAILED DESCRIPTION OF INVENTION
Accordingly, the present invention provides a system for distending body tissue cavities
of subjects by continuous flow imgation dunng endoscopic procedures the said system
comprising
a fluid source reservoir containing a non viscous physiologic fluid meant for cavity
distension.
In yet another embodiment of the present invention, the proximal open end of the fluid
supply tube is constantly and completely immersed in the fluid source reservoir
In still another embodiment of the present mvention, a proximal end of the inflow tube is
connected to the outlet end of the variable speed positive displacement inflow pump and
a distal end of the inflow tube being connectable to the inflow port of the endoscope
instrument.
In a further embodiment of the present mvention, the variable speed positive
displacement inflow pump is selected from the group composing peristaltic pump, piston
pump, gear pump, diaphragm pump and plunger pump
hi one more embodiment of the present invention, the variable speed positive
displacement inflow pump is a penstaltic pump
In one another embodiment of the present invention, the housing tube is releasably
provided between the fluid source reservoir and the inflow tube 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
In one further embodiment of the present invention, a proximal end of the housing tube is
connected to the fluid supply tube near its distal end close to the inlet port of the inflow
pump
In a further more embodiment of the present invention, a proximal end of the housing
tube empties directly into the fluid source reservoir and is constantly and completely
immersed in the fluid source reservoir
In an embodiment of the present invention, a distal end of the housing tube is connected
to the inflow tube near its proximal end close to the outlet end of the inflow pump
In another embodiment of the present invention, the housing tube is provided with a
clamping means at the constnction site to enable the user to vary the diameter of the
housing tube at the constnction site to suit the operational needs of endoscopic
procedures
In yet another embodiment of the present invention, the diameter of the housing tube at
the constnction site is m 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 still another embodiment of the present invention, the diameter of the housing tube at
the constnction site is m the range of 0 01 to 2 5 mm
In one more embodiment of the present invention, 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 mside the cavity
In a further embodiment of the present invention, 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 vanable speed positive displacement
outflow pump
In one another embodiment, the present invention further comprising an outflow pressure
transducer connected between the proximal end of the outflow tube and the inlet end of
the vanable speed positive displacement outflow pump for measuring the pressure in the
outflow tube
In one further embodiment of the present invention, the vanable speed positive
displacement outflow pump is selected from the group compnsmg penstaltic pump,
piston pump, gear pump, diaphragm pump and plunger pump
In an embodiment of the present invention, the vanable speed positive displacement
outflow pump is a penstaltic pump
In 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 device of the present invention further comprising a
micro-controller means electncally coupled to the inflow pressure transducer, the outflow
pressure transducer, the inflow pump and the outflow pump for regulating the operation
of the inflow and the outflow pumps
In still another embodiment, the device of the present invention further comprising a
housing tube having a vanable size constnction site being provided between the outflow
tube and the waste fluid reservoir
In a further embodiment of the present invention, the distal end of the housing tube is
connected to the waste fluid carrying tube
In one more embodiment of the present invention, the fluid supply tube, the inflow tube,
the outflow tube and the waste fluid carrying tube are flexible, disposable and are made
of polymeric material
In one another embodiment of the present invention, the inflow and the outflow positive
displacement pumps are coupled to a common shaft for synchronously operating these
two pumps
In one further embodiment of the present invention, the inflow housing tube is provided
with an electromechanical device, a solenoid, to enable the micro-controller to vary the
diameter of the constnction site
In an embodiment of the present invention, wherein if the inflow and the outflow pumps
are coupled to the common shaft, the inflow housing tube is essentially provided with the
micro-controller controlled solenoid for varying the diameter of the constnction site
In another embodiment of the present invention, the vanable speed inflow and outflow
peristaltic pumps are provided with 1 to 5 penstaltic pump tubes connected m parallel
between the inflow and outflow ends of the penstaltic pumps for reducing the frequency
of pulsations in the pressure, the said tubes being connected to each other at the inflow
and outflow ends of the penstaltic pumps, and the said penstaltic pump tubes being the
ones which come in contact with the rollers of the penstaltic pumps
In yet another embodiment of the present invention, the inflow pressure pulsation
dampening means compnses a single outlet synnge mechanism, the piston of the same
being coupled synchronously to the positive displacement inflow pump through a
coupling means and a single outlet end of the said synnge mechanism being connected to
the inflow tube
In still another embodiment of the present invention, the outflow pressure vanation
dampening means compnses a single outlet synnge mechanism, the piston of the same
being coupled synchronously to the positive displacement inflow pump through a
coupling means and a single outlet end of the said synnge mechanism being connected to
the outflow tube
In one more embodiment of the present invention, if the inflow and the outflow pumps
are operated synchronously by coupling them to the common shaft, the inflow and /or the
outflow pressure variation dampening means are optionally operated synchronously by
coupling them to the same common shaft
In one another embodiment of the present invention, a fluid flow rate sensor is located in
the lumen or wall of the fluid inflow tube for measuring the cavity inflow rate
In yet another embodiment of the present invention, the fluid flow rate sensor is located
between the inflow port of the endoscope and the location where the housing tube is
connected to the fluid inflow tube
In still another embodiment, the device of the present invention further comprises a fluid
flow rate sensor connected between the proximal end of the outflow tube and the inlet
port of the variable speed positive displacement outflow pump for measuring the cavity
outflow rate
In one more embodiment of the present invention, the fluid flow rate sensor is located
between the outflow port of the endoscope and a place proximal to the point where the
said additional/optional housing tube is connected to the outflow tube
In one another embodiment of the present invention, the fluid flow rate sensors consists
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 for measuring the temperature
of the said metal plate, the temperature of the metal plate being a function of the fluid
flow rate
In a further embodiment of the present invention, the fluid flow rate sensor is a hot wire
anemometer
In a further embodiment of the present invention, instantaneous real time rate of fluid
mtravasation is determined by electncally connecting the inflow and outflow fluid flow
rate sensors to a micro-controller
In a further more embodiment of the present invention, the fluid source reservoir, the
inflow pump, the tubes, the tissue cavity, and the out flow pump are placed
approximately at the same height with respect to a honzontal ground
111 another embodiment of the invention the two positive displacement pumps, which may be peristaltic pumps, are attached on a common single central shaft such that a single motor operates both pumps simultaneously and such arrangement being provided as it further reduces fluid turbulence inside the tissue cavity
The proposed invention is descnbed hereafter with reference to the accompanying drawings in order to clearly explain and illustrate the system and the working of the system It is respectfully submitted the scope of the invention should not be limited by the description being provided hereafter
The system of the present invention is a unique system for distending body tissue cavities m endoscopic procedures In the proposed invention a body tissue cavity is distended by continuous flow irrigation in such a maimer that the amplitude of the pressure pulsations created by the positive displacement pumps can be reduced to a negligible value In the proposed invention 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 varying the value of the other parameter
Figure 1 shows the main diagram of the invention In figure 1 the inflow and the outflow 'pressure pulse dampening systems', have been shown clearly However m order understand the invention in a simpler manner, first the basic invention without the 'pressure pulse dampening systems' shall be discussed The basic schematic diagram of the invention is shown in figure 2 Figure 2 is similar to figure 1 except that in figure 2 the two 'pressure pulse dampening systems' have not been included The two penstaltic pumps 5 and 14 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 Figure 2 represents the complete basic schematic diagram of the invention Please note that the controller being used in the system shown in figure 2 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 basic 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 surgeries, it is not essential The controller being used in the present invention merely assists the user in amving easily at some of the additional functions which otherwise can be performed manually Thus, in this manuscnpt the mechanical version of the invention
shown in figure 3 is being discussed m more detail in order to explain the basic physical principals of the invention with a greater clarity
Referring to figure 3, the system shown in this figure comprises of two penstaltic pumps which can maintain a predictably precise stable cavity pressure for indefinite time by working simultaneously at constant rotational speeds Pump 5 pushes fluid into the cavity 18 and while pump 14 simultaneously extracts fluid out of the cavity 18 The inlet end of the inflow penstaltic pump 5 is coimected to a fluid source reservoir 1 via tube 2 The distal open end of tube 2 is constantly submerged in a stenle non viscous physiological fluid like 0 9% normal saline, 1 5% glycine, nnger lactate or 5% dextrose contained mside the reservoir 1 at atmosphenc pressure One end of the tube 7 connects the 'T junction' 3 situated at the inlet end of the pump 5 while the other end of tube 7 connects with the 'square junction' 6 situated at the outlet end of the pump 5 The 'T' junction 3 is thus the meeting point of three tubes, namely 2,4 and 7 Similarly the square junction 6 is the meeting point of four tubes, 4, 9, 7 and 10 The rollers of the peristaltic pump 5 continuously compress and roll over the entire length of tube 4 thus displacing fluid in the direction of the curved arrow This curved arrow denotes the direction in which the rollers of the penstaltic pump 5 rotate Tube 7 has a constnction 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 m companson to the lumen of the rest of the tube 7 Such constnction may be a permanent constnction in the lumen of tube 7 or it may be a vanable constnction whose diameter may be increased or decreased as desired A pressure transducer 17 is attached at one of tube 9 while the other end of tube 9 is connected anywhere on inflow tube 10 For practical convenience it is desirable that the said other end of tube 9 be cormected m the up stream part of the inflow tube 10 such as at the square junction 6 The pressure transducer 17 measures the fluid pressure via a column of liquid or air present in the lumen of tube 9 The fluid pressure as measured by the pressure transducer shall be refened to as P In this manuscnpt the term 'P' shall frequently be used to refer to the actual pressure inside the tissue cavity but in physical terms P is the pressure sensed by the transducer 17 at point 6 The pressure transducer 17 may also be m the form of a membrane diaphragm incorporated m the wall of the inflow tube 10 such that this membrane diaphragm is m direct contact with the fluid contained in
the inflow tube 10, such that the linear movement excursions of the said membrane are niterpreted as pressure of the fluid inside the inflow tube 10 by a suitable pressure transducer Such type of pressure sensor being directly incorporated in the wall of the inflow tube 10 senses the fluid pressure without the intervention of tube 9 The basic purpose of the transducer is to measure the fluid pressure inside the inflow tube 10, such as at point 6, 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 9 shall be continued to be considered in the rest of the manuscript The peristaltic pump 14 attached to the outflow side actively extracts fluid out of the tissue cavity 18 via the out flow tube 12 The outlet end of the pump 14 is connected to a waste fluid carrying tube 15 which opens into a waste fluid collecting reservoir 16 at atmospheric pressure The rollers of the pump 14 constantly compress and roll over the entire length of the peristaltic pump tubing 13 thus displacing fluid in the direction of the curved arrow which also corresponds with the direction of pump rotation
In order to understand the invention m a simpler manner both pumps are being considered to be identical in all respects and all the tubes, the inflow and out flow port are also being considered to be having the same uniform inner diameter However the inner diameter of the tubes and the inflow 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 Tubes 4 and 13 consist of a soft resilient plastic matenal which can be efficiently compressed by the rollers of the penstaltic pumps The other tubes also consist of a suitable resilient plastic material It is assumed that all the components shown m figure 3, including the two pumps, all tubes and the said cavity, are placed at the same honzontal height with respect to the ground Also the rollers of pumps 5 and 14 should press adequately over tubes 4 and 13 in such a manner that there is no leak through these tubes when the pumps are stationary It is also assumed that there is no abnormal leak of fluid in the irrigation system, for example leak via a accidental hole made in any imgation tube or a fluid leak which might occur if the endoscope loosely enters into the tissue cavity, for example in
hysteroscopic surgery fluid leaks by the sides of the endoscope if the cervix is over dilated
One end of the constnction site housing tube 7 instead of being connected with tube 2 at the 'T' junction 3 can also open directly into the fluid source reservoir 1 This shall not affect the efficiency of the system m any way but it may be practically difficult from the surgical point of view in some special cases Thus such a provision is separately shown in figure 6 and the said tube has been labeled as 11 but it has intentionally not been included in figures 1,2 and 3 in order to keep the drawings simple Also a constriction site housing tube similar to tube 7 labeled as 17 can be attached to the outflow tube 12 as shown in figure 6 In the said tube 17 the said constnction site is labeled as 19 Such tube can serve a number of purposes Tube 17 can be utilized for relatively faster evacuation of air bubbles from the cavity The said bubbles are mvanably created inside the cavity as a result of electrosurgical cutting and coagulation or they may enter the cavity while the endoscope is being introduced into the cavity Such bubbles cause extreme nuisance for the surgeon because they obscure vision and thus the surgical time may be greatly increased 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 continuous flow irrigation However in certain situations it may not be possible to bring 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 being 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 19 in the tube 17 However such maneuver tends to completely collapse the cavity Thus if the resctoscope tip is only moderately away from the bubbles the constriction 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 19 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 17 may also be used for quickly flushing air bubbles from the imgation tubes by fully opening the constnction site 19 for
a few minutes or seconds The tube 17 may also be used for any other purpose as deemed fit by the surgeon However the said tube 17 has intentionally not been included m the main block diagrams of the invention because by including the tube 17 in the main block diagrams it would have become very difficult to explain the basic physical principals of the invention However tube 17 is a very beneficial component and is thus recommended to be incorporated in the system of the proposed invention The opening and closing of the constriction site 19 can also be regulated manually to help m vanous special advanced endoscopic applications hicorporation of tube 17 with the vanable constriction site 19 can help in reducing the substantially high amplitude pressure vanations inside the cavity caused by abnormally large cavity wall contractions, but such phenomenon is only rarely encountered Also an additional pressure transducer 63 may also be attached on the out flow tube 12, if desired, as shown in figure 6 However the said pressure transducer 63 has intentionally not been included in the main block diagrams of the invention because by doing so it would have become very difficult to explain the basic physical principals of the invention
In order to clearly understand the system shown m figure 3 it would be helpful to discuss the functioning of the inflow penstaltic pump 5 as a separate entity as shown m figure 4 The rollers of pump 5 move in the direction of the curved arrow and squeeze over the entire length of penstaltic pump tubing 4 Initially tubes 2, 4, 7 and 9 contain air at atmospheric pressure and the firee open end of tube 2 is submerged in a sterile fluid contained inside the fluid source reservoir 1 The moment the constriction site 8 is fully occluded a column of fluid is immediately sucked into tube 4 via tube 2, and thus fluid starts accumulating in the proximal parts of tubes 9 and 7. As the fluid fills m tube 9 it pushes a column of air distal to the fluid column created m tube 9 and the pressure of this compressed air column is sensed by the pressure transducer 17 The fluid pressure and the pressure of the said compressed air column are same thus the pressure transducer 17 actually senses the fluid pressure If tube 7 continues to remain fully occluded at the constriction site 8, the fluid continues to accumulate inside tubes 9 and in that part of tube 7 which lies between point 6 and the constnction site 8, and the pressure transducer 17 thus displays a continuously rising fluid pressure The moment the block at the constriction site 8 is partially released the fluid escapes in the form of a jet through the
partially open constriction opening 8 in the direction of point 3 With the constriction opening 8 being only partially blocked, if the pump 5 continues to rotate at a constant rotational speed the fluid pressure ultimately gets stabilized at a fixed value provided the internal diameter of the constnction site 8 is not further varied The diameter D of the constriction 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 housing tube, that is range between when the constnction site 8 is fully occluded, to a maximum value which is less than the diameter of tube 7 Henceforth in this manuscnpt the inner diameter of the constnction site 8 shall be deemed to be fixed at some predetermined value D, unless otherwise stated
Referring to figure 5, this figure is similar to figure 3 but a limited region of the imgation circuit having an almost same pressure has been shaded black Due to fnctional resistance experienced by the moving fluid the pressure at point 6, as sensed by the transducer 17, is always found to be higher than the actual pressure inside the tissue cavity 18 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 a simulated expenmental endoscopic model, as explained hereafter, such pressure difference was found to be only 2 mm Hg at a out flow rate of 500 ml/mmute, while at outflow rates less than 400 ml/minute this pressure difference was so small that it had not been possible to demonstrate it expenmentally The term 'out flow rate' being referred to the flow rate of pump 14 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 reading of the transducer In this manner, in endoscopic surgeries, it is possible to determine the actual cavity pressure by using the pressure transducer 17 located far away from the cavity This feature is of special relevance because in 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
Referring to figure 3 it shall be first descnbed as to how the system of the proposed invention can be used mechanically, that is without a controller The peristaltic pumps 5
and 14 can be made to work at any fixed rotational speed and the fluid flow rate of each pump 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 14 shall henceforth be denoted by R2 and shall be termed as the 'outflow rate' The fluid flow rate of pump 5 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 true inflow rate for the cavity 18, as might be suggested by the literary meaning of the term 'inflow' because Rl is not the actual rate at which fluid into the cavity 18 because some fluid also constantly escapes through the constnction site opening 8 Henceforth in the entire manuscnpt the term 'inflow rate' shall only be referred to the flow rate of the inflow pump 5 unless specifically mentioned However the term 'outflow rate' R2 does correspond to the literary meaning of the term 'outflow' because R2 is equal to the rate at which fluid flows out of the cavity 18 The surgeon initially decides an out flow rate R2 by selecting a suitable rotational speed for pump 14 Next the surgeon decides the maximum flow rate at which fluid could be allowed to enter into the cavity via the inflow tube 10 and the inflow pump 5 is set to work at such flow rate or at a flow rate slightly lesser than this As already discussed, intravasation is process by which fluid enters into the patient's blood circulation through the cut ends of blood vessels located in the cavity wall or enters into the patient's body, for example mto 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 pumped by the inflow pump 5 can enter into the patient's body at a rate almost equal to 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 in such time a dangerous quantity of fluid might enter into the patient's body If4he 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 fluid starts flowing into the
tissue cavity and the pressure inside the tissue cavity starts nsing When the desired pressure is achieved inside the tissue cavity the diameter of the constriction site 8 is not reduced any further and is fixed The diameter of the constnctions site at this stage 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 constriction 8 has a permanently fixed diameter then only the flow rates of pumps 14 and 5 have to be set before the system becomes completely operational The Inventors here would like to discuss about the importance of incorporating the housing tube 7 with the constnction site and the non-obvious advantages provided by the housing tube 7 with the constnction site
As mentioned earlier, till date the surgeons were left with only two options, either to Ignore the said cavity pressure vanations by not conecting 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 inside 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 controlling the operations of the pumps) only if the fluctuations in the cavity pressure are gradual and not highly instantaneous That is, if the quantitative rise/fall in the cavity pressure is over long time penod, the controller would be able to provide proper conective-action As the time penod to detect variation in the cavity pressure and commence corrective action is ideally m the range of 2 to 4 seconds, if the quantitative rise/fall in the cavity pressure is over very short time penod, the suggested mechanism of providing a controller will be unsuitable Under such instances, 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 penod for the system to once again get stabilized
The haventors have surpnsingly found that by incorporating a housing tube provided with a constriction site at the inflow side as descnbed above, inherently and passively corrects the pressure variations due to physiological cavity wall contractions and the mechanical movement of the tubes and the endoscope and also limits the vanation in the size of the cavity The Applicants would like to highlight that it is important to control both the variations m the pressure inside the cavity and the changes in the size of the distended cavity Large variations in the pressure inside the cavity or the size of the cavity are detrimental 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 this 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 and 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 in the size of the distended cavity The housing tube having the constnctions site provides a by-pass route for the fluid being pushed out of the cavity to go back to the fluid supply tube or the fluid source reservoir This avoids the instantaneous pressure surge inside the cavity which is harmful to the patient The size of the diameter at the constriction automatically controls the amount of fluid passing through the housing tube, thereby controlling the amount of fluid being pushed out of the cavity Inclusion of the housing tube with the constnction site therefore mimmizes the instantaneous variations in the size of the distended cavity
Alternatively if the cavity expands a suitable volume of fluid is sucked into the cavity from the imgation circuit, such as from the region of point 6, and this is accompanied by a corresponding transient decrease m the flow rate at which fluid which fluid is escaping via the constnction site 8 in the direction of point 3 but if the magnitude of the said physiological expansion is more fluid may even be sucked into the cavity via the constriction site 8. This imphes that the constnction site 8 is helping in maintaining a stable cavity pressure despite physiological cavity wall contractions by suitably varying the magnitude of an imaginary fluid 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:
Referring again 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 hi such hypothetical situation as long as R2 and Rl are not altered the cavity pressure P remains predictably constant throughout surgery resulting in a predictably stable mechanical distension of the tissue cavity walls which culminates in constant clear visualization throughout the endoscopic procedure If in 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 increasing the value of Rl and stop doing 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 hi the said hypothetical endoscopic procedure if the outflow rate R2 needs to be increased without altenng the cavity pressure P then the value of R2 is increased 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 altenng 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 already stated The preceding statements shall now be explained by the help of a numerical
hypothetical example In reference to figure 3 considenng a hypothetical situation in which an endoscopic procedure is being done at an outflow rate of 100 ml/minute, an inflow rate Rl and the cavity pressure being 80 mm Hg If the surgeon wants to increase the outflow rate to 322 ml/minute by maintaining the cavity pressure at the same value of 80 mm Hg outflow rate is increased to 322 ml/minute and the inflow rate is increased by 222 ml/mmute, because 322 ml/min - 100 ml/mm = 222 ml/minute As already mentioned in 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/mmute, 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 surgeries but it requires a skilled operator having a detailed knowledge of the physical pnncipals 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 explain more clearly the physical pnncipals associated with the controller based version of the basic invention shown in figure 2 and the main invention shown in figure 1
CONTROLLER BASED VERSION OF THE INVENTION:
Referring to figure 2, this figure shows a schematic diagram of the basic invention without the 'pressure pulse dampening system' Figure 2 and figure 3 are similar except that in figure except that in figure 3 the controller system is not included A tachometer, not shown in the diagrams, is coupled to each penstaltic pump and sends information regarding the pump rotation speed to the controller 19 via wires 60 and 58. The pump flow rates being proportional to the pump rotation speed the tachometer signal always conveys flow rate related information to the controller As already mentioned m paragraph 51 both penstaltic pumps have been considered to be similar in all respects because this makes it easier to understand and operate the system However the two peristaltic pumps may also be different in context with the irmer diameter of the
peristaltic pump tubes 4 and 13 but in such case suitable modifications have to be made in the controller programming in order to operate the system as descnbed in this manuscript The controller also regulates the rotation speed of the two pumps via electncal signals sent through wires 59 and 61 The pressure transducer 17 conveys the pressure signal to the controller via wires 62 On the basis of a pressure feed back signal received from the pressure transducer 17 the controller regulates the rotational speed of the inflow pump 5 The outflow pump 14 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 61 A provision exists by which desired values for P and R2 can be fed into the controller and the values Rl, R2 and P can be continuously displayed via suitable display means incorporated in the controller The controller can be programmed to perform many special functions related to endoscopic surgery
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 input means incorporated in the controller The diameter D at the constnction site 8 remains 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 in figure 2 is operated the controller 19 instructs the outflow pump 14 via wires 61 to continuously extract fluid out of the body cavity 18 at a desired fixed outflow rate R2. Thus all through the surgery the outflow rate remains fixed at R2 mespective of any internal or external factors unless intentionally changed by the surgeon The cavity pressure is sensed by the pressure transducer 17 and a conesponding pressure feedback signal is sent to the controller via wires 62 on the basis of which the controller regulates the inflow rate Rl, via wires 59 After the system is made operational the controller 19 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 determined by the controller by a pressure feed back mechanism and such determination 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 Final' is achieved and is maintained for a desired minimum time interval, for example 10 seconds, after which the controller releases the inflow pump 4 from its pressure feedback control mechanism and allow the inflow pump 4 to operate on its own at an inflow rate 'Rl.Final' which was determined by the controller In this manner the two peristaltic 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 minimum time, which may hypothetically be 10 seconds, the inflow pump 4 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 4 is again allowed to be operated without the pressure feedback mechanism at the newly determined 'Rl.Final' inflow rate. Such sequence of events continue to occur throughout the endoscopic procedure Taking an imaginary example if the total surgical time is 60 minutes then it may be hypothetically possible to operate the inflow pump independent of the pressure feedback mechanism for 55 minutes and under the control of the pressure feedback mechanism for 5 minutes However, provision of operating the inflow pump 4 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 operating the inflow pump 4 independent of the pressure feedback mechanism is to avoid unnecessary corrections of minor pressure vanations caused by physiological cavity wall contractions The concept of physiological cavity wall contractions has been explained in detail under the heading 'basic physics of cavity distension' hi the present invention the physiological vanations in cavity pressure are automatically corrected by the constriction site 8 without the need of a controller If the cavity contracts a imnute quantity of fluid which is pushed out of the cavity escapes via the constriction site 8 towards point 3 It is to be noted that the part of tube 7 between point 8 and 3 is at atmosphenc pressure thus the fluid which is expelled from the cavity as a result of a physiological contraction escapes through the constnction site 8 against a
zero pressure head, which being atmosphenc pressure Thus, the transient, insignificant and instantaneous rise and fall m cavity pressure variations get stabilized 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 imgation circuit, such as from the region of point 6, and this is accompanied by a corresponding transient decrease in the flow rate at which fluid is escaping via the constnction site 8 in the direction of point 3 but if the magnitude of the said physiological expansion is more fluid may even be sucked into the cavity via the constnction 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 of an imaginary fluid flow vector passing through the constnction site 8 Normally the direction of such imaginary vector is always towards point 6 while its magnitude constantly vanes to take care of the pressure changes resulting due to physiological cavity contractions Normally a cavity continuously contracts and dilates by approximately the same magnitudes thus there is no logic to check the minor pressure vanations emanating fi-om the said contractions Also the opening of the constnction site 8 does not allow the said physiological cavity pressure fluctuations to cause any significant cavity wall movement excursions by allowing to and fro movement of flow through its lumen However, if the said pressure changes are made to be corrected by a controller, as is done m the pnor art systems, the cavity wall may exhibit significant irregular pressure fluctuations which may result in 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 4 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' inflow rate is established at which the inflow 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 and the cavity pressure P such that these safe limits are not exceeded accidentally
REMOVING THE OUTFLOW PUMP
Referring to figure 2 the outflow pump 14 can also be totally removed and the outflow tube 12 may be made to drain directly into the waste fluid container 16. In such a case a permanent constnction can also be incorporated inside the out flow tube 12. A vacuum source can also be attached to the waste fluid collecting container 16. However the embodiment described in this paragraph is much inferior to the system of the proposed invention and it is for this reason that schematic diagrams related to this infenor embodiment have not been included in this manuscript. A VARIABLE CONSTRICTION SITE
In context with the system shown in figure 2 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 constnction site 8. The housing tube havmg the constnction site is substantially responsible for dampening the pressure pulsation or mmimizing the turbulence inside the cavity. It however may not provide any substantial dampemng 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 mtermittently regulated by a controller as and when required for example in the eventuality of fluid mtravasation or extravasation thus implying that the diameter D shall be firee 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 described in great detail in the previous paragraphs m context with figure 2. In the vanable constnction system proposed in this paragraph both pumps 5 and 14 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 mflow and outflow rates would be set by feeding suitable flow rate values mto the controller after which the controller would not influence or regulate the said two pumps and the cavity pressure would be maintained only by varying the diameter D at the constriction site 8. In order to vary the diameter at the constriction site 8 a suitable electromechamcal devise such as a solenoid operated devise could be mstalled 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
carried in a controlled maimer and not just by totally opening or totally closing the lumen. The said devise could comprise of a long coil containing a movable long cylindncal magnet and this magnet piece by pressing over the tube, would vary the inner diameter of the tube When current passes through such coil the magnet piece would either be pulled in or pushed out depending upon the direction of the current and the polarity of the magnet and the force which the said long cylindrical magnet piece could apply over the plastic tube would depend upon the current density passing through the coil or in simpler terms the amoimt of electrical energy supplied to the coil, hi context with the present paragraph the controller shall regulated the amount of electrical energy suppUed 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 mvention could be greatly enhanced by incorporating a system of pump synchromzation as described m the next paragraph. The variable constriction site as described m this paragraph has not been included in any of the figures only to keep the manuscript simple. A SYSTEM OF PUMP SYNCHRONIZATION
As discussed m the preceding paragraphs the system of the proposed invention as shown m figures 2 and 3 helps in considerably reducing cavity fluid turbulence. However the two penctaltic pumps create pressure pulsations which in turn causes some turbulence mside the cavity. A method shall now be described to mininuze such turbulence by synchromzing the two peristaltic pumps on a smgle common central shaft. The two positive displacement inflow and outflow pumps 5 and 14, which are preferably penstaltic pumps, can be attached, that is mounted, on a common central dnving shaft which is in turn rotated by a common single motor. Referrmg to figure 7, the two penstaltic pumps 5 and 14 are mechamcally coupled to a common driving shaft 26 which is dnven by the motor 35. The motor 35 can be any suitable motor for example a DC electnc motor. Points 27 and 28 refer to the mechanical coupling sites between the common driving shaft 26 and the pumps 5 and 14 In figure 7 the rollers of the penstaltic pump 5 have been referred to as 20, 22 and 24 and the symbolic attachment of these rollers with the central axis point 27 is denoted by lines 29, 30 and 31 respectively. The
abllers of the peristaltic pump 14 have been referred to as 21, 23 and 25 and the symbohc attachment of these rollers with the central axis point 28 is denoted by lines 32, 33 and 34 respectively The inner diameter of tube 4 related to the inflow penstaltic pump 5 has to be greater than the inner diameter of tube 13 related to the outflow pump 14 and the same had also been diagrammatically depicted in figure 7. The motor 35 rotates the common driving shaft 26 m the direction of the curved arrow located at the extreme right side of the diagram m figure 10. The common driving shaft 26 being mechanically coupled to the two penstaltic pumps, rotates these pumps in the direction of the two curved arrows related to each pump. In figure 7 the rollers of the two peristaltic pumps are seen located at 12 'O clock, 4 'O clock and 8 'O clock positions respectively for both pumps. Let us consider rollers 20 and 25 related to the inflow and the outflow pumps respectively. Let it be assumed that when the motor 35 rotates the diving shaft 26 then it takes a time T for the roller 20 of the inflow pump 5 to move fi-om its initial 12 'O clock position to 4 'O clock position. Let it also be assiuned the outlet end of the inflow pump 5 to be situated at 4 'O clock position As the two pumps are mechanically coupled to the common shaft 26 the corresponding roller 25, related to the outflow pump 14 also takes the same time T to move fi"om its imtial 8 'O clock position to the 12 'O clock position. Let it also be assumed the inlet end of the outflow pump 14 is located at the 8 'O clock position. While the roller 20 moves from the 12 'O clock position to the 4 ' O clock position a positive pulse having a magnitude M1 tends to be created inside the tissue cavity. While the roller 25 moves fi-om the 8 'O clock position to the 12 'O clock position a negative pressure pulse having a magmtude M2 tends to be created inside the tissue cavity As the two peristaltic pumps are synchromzed the said positive and negative pressure pulses havmg magnitudes Ml and M2 tend to cancel or negate the effect of each other and the magnitude M3 of the resultant pressure pulse is equal to Ml - M2. The magmtude of the resultant pressure pulse can be made almost negligible by suitable mechamcal adjustments of the spatial alignment of the rollers of the two peristaltic pumps The roller 20 related to the inflow pump and the roller 25 related to the outflow pump have been termed as 'corresponding rollers' because while roller 20 of the inflow pump creates a positive pressure pulse mside the cavity by pushing fluid into the cavity the roller 25 creates a negative pressure pulse inside the cavity by actively extracting fluid out of the
Itavity. A similar example can also be proposed for corresponding rollers 24 and 23, and rollers 22 and 21. In the system shown in figure 10 the spatial alignment of rollers related to both the pumps can be adjusted experimentally in order to achieve the minimal possible fluid turbulence and once the minimum desired turbulence level is achieved the relative orientation or alignment of the corresponding rollers is not changed. It is clear that the magmtude of the said 'net pressure pulse' depends upon M2, M3 and the relative instantaneous spatial position of the said corresponding rollers. If the inflow and the outflow pumps are not synchronized via the common shaft 26 or if the pumps run at different RPM's the Ml and M2 can never cancel or negate the effect of each other thus leadmg to fluid turbulence. Thus by synchronizing the two peristaltic pumps via the common driving shafl; 26 the fluid flow through the cavity can be made almost pulseless and very close to laminar or a streamline flow.
Thus by synchronizing the two pumps cavity fluid turbulence can mimmized or almost negated. If the two pumps rotate at different RPM's then the relative corresponding positions of the rollers of the two pumps constantly keeps on changing which gives nse to imwanted cavity fluid turbulence. However in the 'synchronized pump system' described m this paragraph the flow rates of the mflow and the outflow pumps cannot be altered independent of each other and if the cavity pressure needs to be varied without changing pump RPM's then the same is possible only varymg the diameter D of the constnction site 8.
A METHOD TO DAMPEN THE PRESSURE PULSATIONS OF A PERisTALTIC PUMP
The 'system of pump synchronization' discussed in the previous paragraphs helps m reducing or dampemng the pressure pulsations created by the two peristaltic pumps thereby it helps in reducing the turbulence inside the tissue cavity. However such system of attaching the two penstaltic pumps on a single common drivmg shaft is practically difficult and it does not allow the two pumps to be run independently of each other thus an easier method of dampening the pressure pulsation of a penstaltic pump is being proposed and the same shall henceforth be referred to as 'pressure pulse dampening system' while the other method is being termed as 'pump synchromzation system'
Referring to figure 4 the fluid pressure, such as at a point 6, is pulsatile in nature because the peristaltic pump 5 constantly pushes fluid via its outlet end in the form of a pulsed manner and not in a continuous manner. Hypothetically assummg that the pump 5 rotates at fixed RPM then in that case the freequency of such pulsations would remain umformly the same all through the operation of the pump. If a graph is plotted for the said pulsations, by relating 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 swings of a predictably fixed amplitude and fixed fi-equency It is to be noted that as the pump RPM is mcreased 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 peristaltic pump comes m apposition with a fixed point, for example the outlet end of the peristaltic pump, some fluid is pushed out fi"om the outlet end of the pump in the form of a bolus. The wave form of such pulsations need not be sinusoidal, but for the sake of an easier understandmg let the said waveform be hypothetically assumed to be sinusoidal in nature. As already stated, if the pump RPM increase then along with the frequency the amplitude of the said waveform also increases. When the pump 5 rotates in the direction of the curved arrow fluid tends to accumulate in tube 9 and m tube 7 between points 6 and 8, and let this cavity consisting of tube 9 and the said part of tube 7, into which the fluid tends to accumulate, be termed as 'fluid accumulation region' In physical terms the said pressure pulsations are produced because the fluid tends to accumulate in the 'fluid accumulation region' in the form of regular pulses wherem each pulse corresponds to a fixed volume of fluid pushed by a roller into the 'fluid accumulation region' m the form of a bolus of fluid. Thus the motion of each roller would correspond to one complete sinusoidal pressure wave. The movement of a single roller in relation to a fixed pomt such as the outlet 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 pomt 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 'single roller movement' be termed as 'single roller time' Assuming the pressure waveform to be a sinusoidal curve, each 'smgle roller movement' corresponds to one complete sinusoidal pressure waveform consisting of a positive
pressure surge followed by a negative pressure surge or vice versa. Also the time penod of the assumed smusoidal wave form would be equal to 'single roller time'. If during the positive pressure surge an adequate volume of fluid is removed from the 'fluid accumulation region' and dunng the negative pressure surge the same adequate volume of fluid is again added back into the 'fluid accumulation region' the sinusoidal nature of the pressure waveform could get dampened and the resultant waveform would get transformed mto an almost straight line curve. The resultant waveform could theoretically be an absolute straight line if the wave form associated with the said process of adding and removing adequate volumes of fluid from the 'fluid accumulation 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 in practical situations. However a substantial dampening of the resultant waveform could be practically achieved if a syringe system was synchronously coupled with the mflow penstaltic pump 5 and the single outlet end of the said syringe system was connected with the 'fluid accumulation region'. Referring to figure 8, this figure is the same as figure 4 except that a said synnge system 38 has been included. The syringe system 38 consists of a piston 39 denoted by a shaded area. The piston 39 moves up and down inside a cylmder 43 while making a watertight contact with the inner walls of this cylinder 43. One end of a straight rod 40 is cormected to the piston while the other end of this rod 40 is connected to a couplmg mechanism 37 housed on a common shaft 36. The coupling mechanism 37 and the peristaltic pump 5, both are attached on to a common shaft 36. The couplmg mechanism 37 is so designed that it converts the rotary motion of the shaft 36 into a linear up down motion of rod 40 which is ultimately mamfested as an up down movement of piston 39 inside the cylmder 43. The up down motion of the rod 40 is denoted by arrows 41 and 42 Thus the shaft 36 is a common shaft which mechamcally operates both, pump 5 as well as the syringe system 38. The direction of rotation of the shaft 36 is denoted by a curved arrow located at the nght end of the shaft 36. The synnge system 38, as the name suggests, resembles a hypodermic synnge used for giving injections to patients. Obviously, the syringe system 38 has only one single opening 44. A tube 45 extending between the opemng 44 and the inflow tube 10 connects the synnge system to the inflow tube 10. Tube 10 is a part of the said 'fluid
Accumulation region' descnbed in this paragraph. Thus the synnge system can be considered to be connected with the said 'fluid accumulation region'. The opening 44 can be referred to as an 'outlet end' or an 'mlet end' because the syringe system can push as well as pull fluid from the 'fluid accumulation region'. However for the sake of convenience henceforth the opemng 44 shall be termed as the outlet end of the syringe system 38. The couplmg mechanism 37 is so designed that the vertical movements of the synnge system can be accurately synchronized with the rotary motion of the peristaltic pump 5. The piston 39 can move up>down>up or down>up>down, depending upon the imtial 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 coupling mechamsm 37 is so designed that while the penstaltic pump 5 rotates by 360 degrees the synnge system correspondingly exhibits 'complete piston movements' which are equal to the number of the rollers of the peristaltic pump. Thus for a penstaltic pump which has three rollers then for each 360 degrees rotation of the penstaltic pump the syringe 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 peristaltic pump. The syringe system is synchromzed with the penstaltic pump via the couplmg mechamsm 37 in such manner that while a roller of the peristaltic pump produces a positive pressure pulse the synnge system extracts fluid out from the 'fluid accumulation region' and while the same roller produces a negative pressure pulse the synnge system pushes an equivalent volume of fluid back into the 'fluid accumulation region'. In order to dampen the pulsations of the peristaltic pump, besides mechamcally synchronizing the synnge system with the peristaltic pump the volume of fluid pulled in or pushed out of the synnge system conesponding to each upward or downward movement of the piston also has to be adjusted accurately, and the same may be done manually by a 'hit and try method'. The volume of fluid pulled in or pushed out by the syrmge system depends upon the linear movement excursion of the piston 39. Also the magnitude of the downward piston excursion is equal to the magmtude of the upward piston excursion, thus the volume of fluid pushed out is always equal to the volume of fluid pulled m dunng each downward or upward movement. Thus the coupling mechamsm 37 has two functions, synchromzation of the synnge system with the penstaltic pump and adjusting
the volume of fluid pulled in or pushed out by the synnge system for each upward or downward movement of the piston The synchronization and the determination of the said volume to be pushed out or pulled into the synnge system are done manually such that a substantial dampening of the pressure pulsations is achieved and once this is achieved the synchronization at the level of the coupling 37 is never again disturbed and the volume of fluid pulled in or pushed out of the syringe system for each movement excursion is also not changed thereafter. After the coupling 37 is adjusted with respect to synchromzation and the volume of fluid to be pulled in and pushed out, the penstaltic pump pulsations shall continue to remain dampened independent of the penstaltic pump RPM and the nature of rotation, that is fixed or vanable RPM. In simpler terms the peristaltic pump pulsations would continue to remain dampened even at a high pump RPM Also the point at which the synnge system 38 is connected to the said 'fluid accumulation region', for example the inflow tube 10, 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 dampemng could no longer be satisfactory. Also preferably the outlet tube 45 of the synnge system should be connected as close to the outlet end of the inflow penstaltic pump as possible. The coupling 37 can be compared to some extent with the conventional CAM system present in automobile engines. Any specific mechamcal design for the coupling 37 is not important, it is the resultant fimction of the coupling 37 with respect to the piston movement, as already described, which is important. The couplmg 37 can have many mechamcal designs. Figure 9 shows one such possible mechanical design for the coupling 37. In figure 9 a small length of the common shaft 36, which is related to the coupling 37, has been made of triangular shape as seen in its cross sectional view and the same is labeled as 49. Let this tnangular part 49 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 thfe 'piston coupler' could also be mcreased or decreased m order to decrease or mcrease the volume of fluid displaced by the cylinder dunng a downward or upward movement of the piston. The central axis point of the 'piston coupler' is denoted by point 48. In case the dimensions of the 'piston
coupler' are chosen to be relatively larger than the dimension of the common shaft 36, the point 48 could also represent the point at which the common shaft 36 passes through the 'piston coupler' and in such a situation the 'piston coupler' 49 could be manually rotated on the common shaft 36 m a clockwise or anti clockwise direction and then locked mechanically at a position which provides the most accurate synchronization. The springs 46 and 47 extending between the inner walls of the cylinder and the piston exert a constant and substantially large upward pull on the piston 39 which causes the rod 40 to constantly be in apposition with the 'piston coupler' 49. The spnngs can be one or more than one in number and the spnngs can also be substituted by any other mechamcal means also which provide an active upward movement of the piston. The 'piston coupler' 49 is assumed to be able to apply a substantially large downward force on the piston 39 via rod 40 such that a corresponding transient negative fluid pressure pulse inside the cyhnder can be totally neglected in the face of the said large substantial downward force Similarly the springs 46 and 47 are capable of puUmg 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 cylinder, this downward movement should be an active movement for which energy is to be denved from the springs from the shaft 36. Similarly the upward movement of the piston should not be aided by the positive pressure pulse inside the cylinder, this upward movement should be an active movement for which energy is to be derived from the springs 46 and 47. The energy for the said upward movement of the piston could also be denved from the shaft 36 if suitable mechanical provision facilitating an active upward movement of the piston could be provided at the level of the couplmg 37.
It is important to note that it is not mandatory to use the said 'pressure pulse dampemng system' with a penstaltic pump only as, with suitable mechanical modifications, the 'pressure pulse dampemng system' could be used beneficially with any type of a positive displacement pump.
The 'pressure pulse dampening system' could also be a mechanism like the 'piston coupler' shown in figure 9 whose rounded edges could directly impinge on a suitable area situated on the outer surface of the 'fluid accumulation region' in a uniform synchromzed
manner, as descnbed, such that this results in continuous umform synchromzed variations in the total volume capacity of 'fluid accumulation region'. The said suitable area on the outer surface of the 'fluid accumulation region' could be a membrane made consisting of a strong resihent polymenc material 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 springs, applied a substantially larger force in comparison to force related with the transient corresponding pressure pulse.
A 'pressure pulse dampening system' presently being descnbed for the inflow pump 5 should be preferably installed on the outflow penstaltic pump 14 also in an exactly similar manner as already descnbed. Thus the said dampening is possible for both, inflow and outflow pumps or for only one single pump, the inflow or outflow one. Obviously the overall effect of the said dampemng as perceived inside the tissue cavity 18 shall be more if the said dampening is done at the level of both the pumps because the pressure pulsations fi"om both pumps travel to the tissue cavity 18 and thus they need to be dampened at the level of both pumps. It is also to be noted that 'pressure pulse dampemng system' is different from the 'pump synchromzation' system accomphshed by housing the two peristaltic pumps on to a single common shaft, while in the 'pressure pulse dampening system' both the peristaltic pumps are housed on separate shafts. 'Pimip synchronization' is more difficult to achieve when compared to the 'pressure pulse dampening system', however the two methods can also be utilized simultaneously but m that case both the peristaltic pumps shall have to be attached on to the same common drivmg shaft.
In figure 1 the inflow 38 and the outflow 55 syrmge systems have been shown synchromzed with the inflow and outflow peristaltic pumps 5 and 14 respectively. In the outflow synnge mechamsm the common shaft houses the coupling 51 which moves the piston 54 via shaft 63 inside the cylinder 64 whose outlet opemng 56 is connected to the outflow tube 12 via tube 57. The coupling system shown in figure 9 would be applicable to this outflow synnge system also.
The pressure dampemng mechamsm descnbed m the present invention is an active pressure dampemng system and not a passive dampemng system. The Applicants have
trealized that only active pressure dampening systems as discussed above provide
substantial dampemng to the pressure pulsation caused by the penstaltic pumps and
relying on passive factors such as the inherent resistance to the flow of the liquid etc do
not provide any effective pressure dampening Further, the pressure dampening system
may not provide any substantial dampemng to the pressure pulsation caused by the
physiological contractions of the cavity walls.
A SYSTEM OF INCORPORATING MULTIPLE PER IS TALTIC PUMP TUBES
In the preceding parts of the manuscnpt the two penstaltic pumps 5 and 14 are shown to
have one single tube each, that is tubes 4 and 13 respectively, which come in contact with
the rollers of the penstaltic pumps. Arbitranly refemng to the inflow pump 5,

(Equation Removed)

where R2 = Flow rate of pump 5, B = inner diameter of the 4
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 R2 doubles. Similarly if
L doubles then also for RPM the flow rate R1R2 doubles. However keeping in mind the
mechanical constramts the values B and L cannot exceed a certain practical value.
However if two tubes like tube 4 are used in parallel m the pump 5 then the mathematical
expression for the flow rate could be written as follows.

(Equation Removed)

This imphes that if two peristaltic pump tubes are used mstead 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 mimmal as possible if the flow rate is not compromised. Thus this system of incorporating 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 irrigation fluid enters into the patient's body system and if excess volume of fluid is intravasated it can be dangerous to the patient's hfe. Thus, keeping in 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 inventors propose that one fluid flow rate sensor each be incorporated in the inflow tube and the outflow tube. Referring to figures 1, 2 and 3 the inflow flow rate sensor should be located m the inflow tube 10 anywhere between the inlet port of the endoscope and the point at which the distal end of the constriction site housing tube 7 is connected to the inflow tube, such as point 6. Such a flow rate sensor would measure the rate at which fluid enters into the tissue cavity 18 and the same is being termed as 'cavity inflow rate'. Obviously the 'cavity mflow rate' is the true inflow rate for the tissue cavity. Similarly the outflow flow rate sensor should be located anywhere in the out flow tube between the outflow port of the endoscope and the mlet end of the outflow penstaltic pump 14 or any other outflow positive displacement pump. However if an additional or optional constriction site housing tube 17 is also connected to the out flow tube 12 as shown in figure 6 then the outflow flow rate sensor should be located between the outflow port of the endoscope and the point at which the proximal end of the constriction site housmg tube 17 is connected to the outflow tube 12. The outflow flow rate sensor measures the rate at which fluid is extracted fi-om 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 intravasation, being termed as R3, can be determimng by subtracting R2 fi-om the 'cavity inflow rate', the mathematical expression for the same bemg 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 comprise of a heating coil in physical contact with a metal plate for heating the same and a temperature sensor placed m 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 fi-om the 'cavity inflow 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
Itntravasated over a certain time interval. The said temperature related flow rate sensor
could be a 'hot wire anemometer'.
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 ammal tissue cavities also and also for
imparting traimng in endoscopic surgenes related to animal tissue cavities.
It is believed that the foregomg description conveys the best imderstanding 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 fi-om the departmg fi^om the spint and
scope thereof
THE INVENTION is UNIQUE
There is no other prior art system in which the amplitude of pressure pulsations produced
by a positive displacement, like a peristaltic pump, could be minimized to a negligible
level. Also the concepts of 'pressure pulse dampening system', 'system of pump
synchromzation', determination of the instantaneous rate of fluid intravasation by using
two hot wire anemometers and the concept of installmg two or more peristaltic tubes in
parallel have not been descnbed in any pnor art system
THE HEART AND SOUL OF THE INVENTION
The 'pressure pulse dampemng system' using a syringe mechanism is the heart and soul
of the mvention without which the invention caimot 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 m the mitial phase of
their leanung 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 along with the corresponding disadvantages of the prior art systems:

(Table Removed)

CONCLUSION
The proposed invention is novel and unique The invention relates not only to increasing surgical efficiency m certain endoscopic procedures but it also helps in preventing human morbidity and human mortality m 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 fluid source reservoir containing a non viscous physiologic fluid meant for cavity distension;
a fluid supply conduit tube cormecting the fluid source reservoir to an inlet end of a variable speed positive displacement inflow pump and an outlet end of the said inflow pump being connectable to an inflow port of an endoscope instrument through an inflow tube for pumping the fluid at a controlled flow rate into the cavity, the flow rate at which the fluid enters into the cavity via the inflow tube being termed as the cavity inflow rate;
an inflow pressure transducer being located anywhere in the inflow tube between the outlet end of the inflow pump and the inflow port of the endoscope; an inflow pressure pulsation dampening means connected to the inflow tube for dampening the pressure pulsations inside the cavity created by the positive displacement inflow pump,
an outflow port of the endoscope being connectable to an inlet end of a variable speed positive displacement outflow pump through an 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 outflow pressure pulsation dampening means connected to the outflow tube for dampening the pressure pulsations inside the cavity created by the positive displacement outflow pump;
an outlet end of the outflow pump being connected to a waste fluid collecting container, and
a housing tube having a controllable constriction site is being provided between the fluid source reservoir and the inflow tube such that the same by-passes the inflow pump; wherein housing tube provides a route for any excess fluid being pumped by the inflow pump to bypass the inflow pump and go back to the fluid supply tube or the fluid source reservoir, thereby minimizing turbulence inside the
cavity and maintaining the cavity pressure at a stable value despite physiological contractions of the cavity wall.
2. A system as claimed in claim 1, wherein the fluid source reservoir containing the non-viscous physiologic fluid is maintained at atmospheric pressure or at a pressure greater than the atmospheric pressure.
3. A system as claimed in claim 1, wherein a proximal open end of the fluid supply tube is connected to the fluid source reservoir and a distal end of the tube is connected to the inlet end of the variable speed positive displacement inflow pump.
4. A system as claimed in claim 3, wherein the proximal open end of the fluid supply tube is constantly and completely immersed in the fluid source reservoir.
5. A system as claimed in claim 1, wherein a proximal end of the inflow tube is connected to the outlet end of the variable speed positive displacement inflow pump and a distal end of the inflow tube being connectable to the inflow port of the endoscope instrument.
6. A system as claimed in claim 1, wherein the variable speed positive displacement inflow pump is selected from the group comprising peristaltic pump, piston pump, gear pump, diaphragm pump and plunger pump.
7. A system as claimed in claim 6, wherein the variable speed positive displacement inflow pump is a peristaltic pump.
8. A system as claimed in claim 1, wherein the housing tube is releasably provided between the fluid source reservoir and the inflow tube 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.
9. A system as claimed in claim 1, wherein a proximal end of the housing tube is connected to the fluid supply tube near its distal end close to the inlet port of the inflow pump.
10. A system as claimed in claim 1, wherein a proximal end of the housing tube
empties directly into the fluid source reservoir and is constantly and completely
immersed in the fluid source reservoir.
11. A system as claimed in claim 1, wherein a distal end of the housing tube is connected to the inflow tube near its proximal end close to the outlet end of the inflow pump.
12. 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.
13. 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.
14. 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.
15. 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.
16. 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.
17. A system as claimed in claim 1 further comprising an outflow pressure transducer connected between the 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.

18. 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.
19. A system as claimed in claim 18, wherein the variable speed positive displacement outflow pump is a peristaltic pump.
20. 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.
21. A system as claimed in any one of claims 1 to 20 further comprising a microcontroller means electrically coupled to the inflow pressure transducer, the outflow pressure transducer, the inflow pump and the outflow pump for regulating the operation of the inflow and the outflow pumps.
22. 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.
23. A system as claimed in claim 22, wherein the distal end of the housing tube is connected to the waste fluid carrying tube.
24. A system as claimed in claim 1, wherein the fluid supply tube, the inflow tube, the outflow tube and the waste fluid carrying tube are flexible, disposable and are made of polymeric material.
25. A system as claimed in claim 1, wherein the inflow and the outflow positive displacement pumps are coupled to a common shaft for synchronously operating these two pumps.
26. A system as claimed in any one of claims 1 to 25, wherein the housing tube is provided with an electromechanical device, a solenoid, to enable the microcontroller to vary the diameter of the constriction site.
27. A system as claimed in claims 25 and 26, wherein if the inflow and the outflow pumps are coupled to the common shaft, the housing tube is essentially provided with the micro-controller controlled solenoid for varying the diameter of the constriction site.
28. A system as claimed in claims 7 and 19, wherein the variable speed inflow and
outflow peristaltic pumps are provided with 1 to 5 peristaltic pump tubes
connected in parallel between the inflow and outflow ends of the peristaltic
pumps for reducing the frequency of pulsations in the pressure, the said tubes
being connected to each other at the inflow and outflow ends of the peristaltic
pumps, and the said peristaltic pump tubes being the ones which come in contact with the rollers of the peristaltic pumps.
29. A system as claimed in claim 1, 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 a single outlet end of the said syringe mechanism being connected to the inflow tube.
30. A system as claimed in claim 1, 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 inflow pump through a coupling means and a single outlet end of the said syringe mechanism being connected to the outflow tube.
31. A system as claimed in any one of the preceding claims, wherein if the inflow and the outflow pumps are operated synchronously by coupling them to the common shaft, the inflow and /or the outflow pressure variation dampening means are optionally operated synchronously by coupling them to the same common shaft.
32. A system as claimed in claim 1, wherein a fluid flow rate sensor is located in the limien or wall of the fluid inflow tube for measuring the cavity inflow rate.
33. A system as claimed in claim 1, wherein the fluid flow rate sensor is located between the inflow port of the endoscope and the location where the housing tube is connected to the fluid inflow tube.
34. A system as claimed in claim 1 further comprising a fluid flow rate sensor connected between the proximal end of the outflow tube and the inlet port of the variable speed positive displacement outflow pump for measuring the cavity outflow rate.

35. A system as claimed in claim 34, wherein the fluid flow rate sensor is located between the outflow port of the endoscope and a place proximal to the point where the said outflow housing tube is connected to the outflow tube.
36. A system as claimed in claims 32 to 35, wherein the fluid flow rate sensors consists 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.
37. A system as claimed in claims 32 to 36, wherein the fluid flow rate sensor is a hot wire anemometer.
38. A system as claimed in claims 32 to 37, 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.
39. A system as claimed in claim 1, wherein the fluid source reservoir, the inflow pump, the tubes, the tissue cavity, and the out flow pump are placed approximately at the same height with respect to a horizontal ground.