FIELD OF THE INVENTION

The present invention relates generally to electrosurgical system. More particularly, the invention provides a system for testing the electromagnetic interference generated due to electro surgical generator and intelligently displaying the physiological parameters on the patient monitor(s).

BACKGROUND AND THE PRIOR ART

In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices have been developed for monitoring many such physiological characteristics. Such devices provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, such monitoring devices have become an indispensable part of modern medicine.

One technique for monitoring certain physiological characteristics of a patient is commonly referred to as pulse oximeter, and the devices built based upon pulse oximeter techniques are commonly referred to as pulse oximeters. Pulse oximetry may be used to measure various blood flow characteristics, such as the oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and/or the rate of blood pulsations corresponding to each heartbeat of a patient. In fact, the "pulse" in pulse oximetry refers to the time varying amount of arterial blood in the tissue during each cardiac cycle.

Electromagnetic interference caused by cautery poses a major performance hazard to many * medical equipment. In pulse oximeters, cautery causes electromagnetic interference which affects the acquisition of analog signals from the finger of the patient.

The present invention details the method used to simulate such cautery effects and resolve them. One of the issues related to resolving cautery effects is that once implemented it is difficult to validate without field trials. The simulation setup explained herewith offers a simple method to simulate such effects in an office environment. The test setup comprises an ESU generator attached to an ESU pencil, patient plate, a pulse oximeter attached to the finger sensor and a beaker containing saline solution. For simulation, the connected patient plate is dipped in the solution and the ESU pencil tip is made to come in contact with the solution. Also the sensor is connected to the patient and his fingers are dipped in the saline solution. With this setup, activation of the pencil will produce noise in the spo2 waveform recorded in the pulse oximeter.

The patient plate in the disclosed new invention provides a least resistive return path for the HF current supplied by the ESU generator thus ensuring the subject doesn't come in the path of the HF current produced and no electric shock is felt. The high frequency electromagnetic radiation & noise current generated by the ESU pencil activation is absorbed by the subject and the noise can be observed on the patient monitor display.

The cause of interference in the spo2 waveform was found to be due to electromagnetic coupling between pulse oximeter module and acquisition card. Hence copper shielding was used which isolates the two cards and prevents any coupling between them.

PRIOR ART REFERENCES

The Indian patent no. 114316, filed on January 1968, titled "improvements in or relating to electrical dental anesthesia "discloses "electrical dental anesthesia using galvanic & faradic currents. This is achieved by using an electric waveform generator using a.c. motor, d.c. generator, induction coil & galvanic cells.

The US patent 3601126 filed during 1969 and assigned to Electro Medical Systems discloses Electrosurgical apparatus including electrodes powered by high frequency electric current, wherein the amplitude of the current flowing through the circuit is monitored and compared with a reference amplitude so that the current source can be regulated to transmit power of a desired amplitude.

Yet another United States Patent 4243045 Filed on 23 January 1979 , Titled " Method and apparatus for the suppression of interference signals in a useful signal" discloses a method where an occurring useful signal having possibly superimposed interference signals is supplied to an interference hum filter. The filtered-out interference hum component is opposing superimposed on the original signal for the purpose of compensation of the interference hum. This applies only for such a length of time as there are no interference pulse peaks recognized by a recognition installation. If such an interference pulse peak is recognized, the filter is disconnected from the input signal and switched over to self-oscillation operation. An artificial oscillation with an amplitude and frequency equal to that of the previously selected interference hum component is then generated without a phase jump and superimposed on the useful signal. The interference pulse peak is simultaneously blanked out. The drawbacks is, Since the physiological signals from patient are real time signals generating equal signal and superimposing is quite cumbersome and difficult with fast changing signals.

Yet another United States Patent 4800894 Filed on November 1986, Titled "Protection of EKG monitor against electrical surgical interference" assigned to Medical Research Laboratories discloses a protective device for an EKG monitor for use in surgical electro-cautery which employs an electro-cautery surgical knife supplied with radio frequency power and an EKG monitoring apparatus having an input and including a scope providing an EKG display. Electrodes are provided for attachment to a surgical patient and are connected to the apparatus by the protective device, which includes a radio frequency detector and disabling apparatus which removes signal from the EKG monitor input in the presence of radio frequency energy.

The drawbacks are in disabling the patient monitor which jeopardizes the safety of the patient and also the spo2 noise removal is not disclosed.

The present invention provides a system and a method which helps in suppressing the electromagnetic interference caused by cautery / electrosurgical generator noises and displaying the noise free signal on the patient monitor for correct monitoring of the physiological characteristics.

The inventor of this invention felt that there is a need to provide a simple yet effective solution either to remove the noise or display the physiological signal with numerical parameters, without noise.

OBJECTS OF THE INVENTION

One object of the present invention is to overcome the disadvantages / drawbacks of the prior art.

The basic object of the present invention is to provide a system and method for detecting, estimating and suppressing the electromagnetic interference generated from electro surgical generators placed nearby the patient monitor.

Another object of the present invention is to provide system and method for testing interference with ECG and displaying the noise free signal on the patient monitor.

Another object of the present invention is to provide a system and method for testing interference with SP02 /pulse oximeter finger probes and measure the noise generated on the PMS display.

Yet another object of the present invention is to design a simulation setup which offers a simple method to simulate such effects in a design office or environment

These and other advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

According to one of the aspect of the present invention there is provided an electrosurgical system for testing the electromagnetic interference and displaying it on the patient monitor. The system comprises an electrosurgical generator, said electrosurgical generator generating power output; plurality of electrode means operatively connected to said electrosurgical generator at distal end through one or more electrical connectors for circulating high frequency current in the system; at least one sensor means for sensing physiological parameters; a yoke having noise filtering circuit connected to said sensor means at one side; a display means for displaying the sensed physiological parameters; wherein said display means comprising noise detecting and filtering circuitry to block the electromagnetic interference and display the electromagnetic interference free signal on a display screen.

Another aspect of the present invention there is provided a method for detecting and suppressing the electromagnetic interference comprising the steps,

a) Filtering an input signal received from a yoke by filter means and allowing the ECG signal to reach the motherboard and displaying as it is, when there is no noise.

b) checking for noise signal in ECG and amplifying and separating the noise using high pass filter means , buffering, isolating using linear optical isolator so that ESU-DET signal is provided for PIC controller.

c) Allowing the PIC controller to make decision about whether to make C AUTDET output high and the duration for which this signal to be high so that the motherboard will display the previous legible and stable value on the output display.

d) allowing the motherboard to make the decision on whether to show the real time physiological parameters as it is, when there is no noise interference or the value of the said parameters 516 crossing the high and low limit ( 520) so that the alarms 508 and 540 are not inadvertently activated during the noise.

e) Allowing the said motherboard to make decision on further displaying the previous legible value for next 10 seconds or more whenever noise is detected and the value to be displayed at 516 is within the set limit of 520

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which: Figure 1 Illustrates Overall view of a system for testing noise interference generated by electro surgical equipment on spo2 finger probes which,in turn the connected to PMS system.

Figure 2 illustrates another setup to measure interference noise on ECG signal generated by electro surgical current flowing through human body and absorbed by humanpatient. Figure 3 illustrates one of the circuit used for filtering the ESU noise on the electro-cardiograph leads RA & LA & the excess noise detecting circuit. Figure 4 illustrates the excess ESU noise detection circuit with high voltage isolation ESUDET signal out. The signal thus generated is given to a PIC microcontroller for verification & then fed to a single board computer.

Figure 5 illustrates the PIC controller working in cooperation with SOM motherboard for detecting the ESU_DET signal which is used by the SOM to take a decision about displaying the relevant parameter on the TFT-LCD display.

Figure 6 illustrates shield placement and method of shield functioning when used with spo2 sensor and circuit disclosed in Fig. 1to attenuate the HF surgical noise

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.

Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures

DETAILED DESCRIPTION OF THE INVENTION

(BEST MODE OF EMBODIMENT)

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

The Fig. 1-Drawing 100 illustrates overall view of a system for testing noise interference due to electro surgical equipment on spo2 finger probes & the connected PMS system. The purpose of this test is to simulate surgical environment where the HF energy passes through the patient's body during surgery, substantially sending the same current through the human body as in the Operation theatre without causing harm to the human subject and without putting a person on the surgery table. The full effect of surgical current is realized without the spray, cutting, coagulating effects.

Part 102 is electro surgical generator which can provide a variable power output of 600 watts, 2000 volts ac and current of 2 ampere by way of an example. This output power is delivered to the patient's body through an electrical cable 104 having an electrical connector cooperating with the surgical generator at distal end and an electro-surgical knife called "pencil" at the patient's side. For the normal use of surgical procedures which are performed inside the operation theatre, the entire current is concentrated at the sharp tip of the pencil 130. The sharp tip of the pencil electrode 130 will be having cutting effect on the patient's body wherever it is touching the patient's body and the current flows due to the activation of 102.

But in this inventive test setup, the full load current is desired to be flown through the electrical cable, so that the noise generated is measured but it should not have the harmful effect of the surgery. This is achieved by the following test setup. The part 122 is an electrically insulated borax glass or polycarbonate plastic beaker which can withstand HF high voltage power and also is anticorrosive. In this particular case it can withstand a voltage of 10,000 volt & maintain its insulation properties up to the frequency of 700 kilo hertz. This beaker 122 is filled with salt water up to 2/3 of its volume. The common table salt chemically known as sodium chloride is added to distilled water so that it is substantially conductive for the test setup. This solution is frequently agitated with a glass stick means so that salt is not precipitated & the conductive properties of the solution are maintained. Other chemicals or electrolytes which become electrically conductive can also be used.

An electrically conductive ground pad 124 also known as neutralpad or return pad or dispersive pad or patient grounding return electrode pad is entirely immersed in the saline/ salt water 128 inside the beaker 122. This is to ensure that the maximum conductivity is achieved so that maximum load current is passed from the electro surgical generator 102. This pad 124 is connected with a cable similar to the electrical cable 104 at the distal end which is connected to 102.

With this, the power from the electro surgical generator 102 is delivered to the beaker ; 122 containing salt water solution / saline solution 128 through the connector 104 & the electro-surgical pencil 130. The electrical circuit is complete through 104,130,128,124, when the pencil knife 130 touches the saline solution 128 and current passes through it.

It has been found by the inventors that when the hand 106 or any other body part of human subject 110 is immersed inside the salt solution 128 and an electro-surgical current is passed between 130 and 128, the HF noise current is picked up by the hand. This noise current intern is picked up by any medical accessories connected to the human body and is displayed on the patient monitor connected thereon. The maximum noise is generated when the pencil 130 is moved substantially away from the 128 so that a visible &audible spark 126 is generated when an air gap of say 5 to 10 millimeter is created.

The part 114 is a patient monitor which has to be tested for the noise immunity from the ESU 102. This is also called "The device under test (DUT)". This contains analog circuits to accept various physiological signals from the 110. The part 118 is called connector panel comprising of various electrical connectors mechanically & electrically cooperating with patient interface cables & sensors. The part 120 is one such connector connected to the yoke 112 & pulse oximeter- finger sensor 108.

The finger sensor 108 contains RED/INFRARED light emitting diodes & photo detectors installed on opposite side of the finger. The RED/INFRARED light passes through the blood flowing through arterioles of the finger (hand 106)& the weak light signals are sensed by the photodiode. These week signals of the order of mV- millivolt areamplified, filtered from noise & fed to a custom designed embedded motherboard 332.

The motherboard 332 converts these analog signals into digital & displays on a TFT-LCD flat panel display 116. Although the patient or human being 110 is essential for testing the invention disclosed herein, it should be appreciated by the reader of this disclosure that other test subjects like bathing sponge/ loofah, potato, bathing soap, watermelon all soaked in electrically conductive salted water can be effectively used.

When the pencil 130 is movedsubstantially away from the 128 salt water surface to create a spark 126. This will create a maximum electrical noise in salt water 128. The human hand 106 which is a part of human subject 110 is substantially submerged in the solution 122. The thumb is not submerged inside the salt water 128 and a finger probe sensor 108 is connected. This finger probe 108 also called pulse oximeter finger probe sensor and is used to measure the saturation level of oxygenated hemoglobin in the arteriole blood flowing through the finger. This sensor is connected to the yoke 112 which can be used to incorporate various noise filter circuits. The connector 120 is used to connect the sensor 108 to patient monitor 116. The extracted signals from 108 are processed and displayed on 116.

The noise picked up due to saline 128 are conducted through hand 106 but no shock is felt or no physical harm is done to 110 since the current flowing between saline 128 & pencil knife 130 is high frequency RF current with skin effect. The skin effect means the current passes through the skin surface and also not sensed by the body since nerves are insensitive to HF.

But this is picked up by PMS114 & noise is displayed on the 116 along with spo2 signal. The various filter circuits can be incorporated inside 112 to curb this noise and the effect can be seen on display 116 before and after implementation.

One of the particular solution to reduce the noise is placing various shielding plates manufactured from insulating plastic sheet &disposing conductive copper plate & noise absorbing ferrite sheets in between.

These sheets are placed inside the 114 or 112 so that the noise is absorbed & grounded. These noise absorbing sheets are also placed behind connector 118 to create the isolation barrier between the cable 120 & signal processing circuits residing inside Patient monitor 114. These noise absorbing sheets are electrically grounded. The detailed graphical depiction & the method of functioning is further disclosed in Fig. 6 part 600 which will be explained again in this disclosure.

Figure2 illustrates another setup to measure interference noise on ECG(electrocardiograph) signal due to electro surgical current flowing through human body.

Part 102 is electro surgical generator. This is similar to the one shown in Fig 1. The output is applied to human voluntary subject 110 through two electrically conductive &dispersing pads 208 & 210 between which the electrical current flows. The electrically conductive patient plate 210 will have electrically conductive adhesive at the bottom surface due to which 210 sticks firmly to 110.

The silicon rubber insulated cable 216 connects pad 210 & pencil electrode 130. Part 222 is another silicone rubber cable connecting the generator 102 to the patient plate 220 to complete the circuit. Part 104 is another silicone patient cable connecting generator 102 with the human subject 110 through the dispersive patient plate 208.

The hydrogel ECG sensing electrodes 202,204,212 are placed near right arm(RA), left arm(LA) & right leg(RL). The ECG signals from the heart of 110 are picked up through lead wires 206, yoke 214 and the connector 218. This connector 218 is connected to the connector panel 118 &patient monitor under test-116.

The clean, stable & legible ECG waveforms &signals are displayed on 116 when the 102 is not activated. When 102 is activated & the pencil knife 130 touches the silicone patient plate 220, the HF current will flow due to which the additional noise signals are picked up by 202,204,212 and the noisy ECG waveform is displayed on the display 116.

When the pencil knife 130 is slightly moved away from the pad 220 to create an air gap of say 5mm, the noise generated by the 102 will be maximum due to the spark 126.

The various noise filtering circuits can be accommodated inside the yoke 214 and the difference in performance can be measured on 116.

Purpose of the test is to simulate surgical environment where electro ESU energy passes through the body during surgery. The essence is sending the same current as in OT without causing harm to the human subject. Without putting a person on the surgery table, without any harm to the patient realizing the full effect of electro-surgery. With this inventive setup, there will be low density power on both side of electrodes.

The entire load current generated by 102 is circulated through 104,208, patient 110, 210, 216,130, the spark 126, the patient plate 220, return cable 222.

The clean signals before activation, the noisy signals during the activation of 102 and the reduced noise due to various noise reducing schemes implemented as in Fig 3,Fig 4 and Fig 5 can be seen on the display 116 of the patient monitor 114.

The Fig 3 shows the detailed embodiment where, the circuit diagram 300, which will detect the HF noise signal overriding low frequency ECG signal & give an "ESUOUT" signal to inform the micro controller to stop displaying the real time numeric value related to the ECG.

Referring to Fig.2, Part202, 204,212 are ECG electrodes picking physiological signals from the subject 110. For simplicity only 202 & 204 are taken and 212 is left out. These signals travel through leads 206 & yoke 214 and reach the connector 218. The connector 218 is electrically & mechanically communicates with the monitor 116. The circuit disclosed in Fig.3 can reside inside 114. The part 302, 306,316,320 are precision resistors with value of say, 100 kilo ohm and a tolerance of+/_ 0.01 kilo ohm. The parts 304,308,318,322 are precision capacitors with capacitance value of say 470 pico farad with tolerances of */_0.1 pico farad.

The resistors 302, 306,316,320 & capacitors 304,308,318,322 together with buffer amplifier 310& 324 form low pass RC filter. This filter also be called as electro surgical noise filter or diathermy filter. In most of the cases this filter or the similar filter installed inside the yoke 214 will block the HF surgical noise from 102.

With these component values, the filter will cut off the noise signals with frequency below 3300 Hertz. Most of the time this arrangement is suffices to reject the unwanted noise & allow the substantially clean ECG signal for further processing. But it has been observed that during the practical surgical environment the noise power carried by the lead set 206 is much higher than what can be rejected by the filter capacity. This excess noise will appear at the impedance buffer amplifier 310,324 & instrumentation amplifier 314. The resistor 312 is used for feedback/ amplifier gain setting purpose. The capacitor 326 is ripple filtering capacitor used between 5 volt & -5 volt supply. This will absorb power supply ripple noise, ESU noise.

The instrumentation amplifier 314 will amplify the filtered ECG signals & the output PADET1 will be given to analog to digital signal converter 328. The digital output is fed to 330 - ECG signal microprocessor. This microprocessor will analyze the ECG signal & the output is numerical value of the ECG signal comprising pulse rate, heart rate, heart rate variability. The waveform signal output will comprise ECG waveform. This output in digital form will be given to computer motherboard or single board computer 332. The TFT-LCD display 116 is digitally communicating with the motherboard 332 & all the numerical parameters & waveforms are displayed to the caregiver or surgeon along with the graphical user interface. The motherboard 332 can decide about whether the particular numerical value or waveform has to be displayed or not on 116 depending upon the noise level from 102 & legibility of the numerical value.

It has been experimented several times &observed by the inventors of this invention that this occurrence of excess noise is for brief period of time where the changes occurring in physiological signals of the patient will not jeopardize the health. At the same time this noisy signal will mess up the waveform & the numeric on the display 116 by which the caregiver / surgeon /intervenist will not be able to make out any legible conclusion with noisy waveform & rapidly varying numerals.

So there is a need to design a vital sign patient monitor which can momentarily display the previously acquired legible value of heart rate instead of real time value during the excessive noise & then return to the real time value so that the more stable display is shown to the Caregiver. The previous legible value means the numerical value which was acquired 10 seconds or 20 seconds earlier to the current corrupted value.

The method used to do this is as follows. When excessive noise appears near instrumentation amplifier 314, it will be naturally crossing the filter &will reach the impedance buffers/unity gain amplifier 334.

The resistors 336,342,340 and the capacitor 338 along with operational amplifier 344 makes a high pass filter where the function will be exactly opposite to 302,306,316,320,304,308,318,322. Here only the HF surgical noise from 102 will be allowed to pass through. The output signal ESUOUT is further fed to the circuit shown in Fig 4 Part 400.

The Fig 4, part 400 gives detailed circuit diagram of enhancing & isolating of ESU noise signal, analog optical isolatorand generation of ESU-DET signal.

The circuit comprising resistors 402,408,410,414,418,420,426 & capacitors 406,404,412 will further filter the HF surgical noise signals & amplify using transistors 422 & 424 so that a linear opto-coupler 428 can be driven which provides the high voltage galvanic type isolation from ESU 102. This will prevent the high voltage related damage to digital circuits like 330, 332,116. The opto-coupler 428 will contain one linear LED (light emitting diode) and photo sensor to convert the electrical signals into light signals and back to electrical signals using photo-sensor.

The secondary side of 428 contains output amplifier &filter. This is made from resistors 430,434,436,440, 444,446,450 & capacitors 442,448,452 along with transistors 432,438. The circuit is designed in such a way that if ESU noise level from 102 crosses certain predetermined level, the noise is amplified and given out as 454 (ESU-DET). This HF signal is then fed to a PIC micro controller 502.

Figure 5 illustrates the PIC controller working in cooperation with SOM motherboard for detecting the ESUDET signal which is used by the SOM to take a decision about displaying the relevant parameter on the TFT-LCD display.

The PIC controller 502 contains suitable circuits which can be configured to the purpose of solving the noise problems. The output signal 454 (ESUDET) is applied to the pin of 502 inside which decides about giving output 504. This output high signal depends upon whether the HF signal input is crossing certain duration like 5 seconds or 10 seconds & amplitude of the signal. If noisy condition is satisfied then output is given to SOM 332. The 332 can be single board computer, System on motherboard, single chip computer and the like.

The interrupt occurrence in 502 due to 454 ( ESU-DET) will lead the program to run the interrupt service routine (ISR).Therefore the output such as "504->CAUT_DET" made high, kept high for 10 second then making it low.

The function of the interrupt service routine (inside 502) is to perform the delay allocated such as 10 seconds in the following pattern,

• Clear the interrupt flag( to erase/flush the previous value).
• Check for 454(ESU_DET) signal for HF noise signal in the form of digital pulse trains.
• If these pulse trains are found then Make the 504,CAUT_DET pin high.
• Introduce 10 seconds delay so that CAUTDET is kept high irrespective of the 454 is LOW.
• ResetCAUT_DET pin low and exit ISR (interrupt service routine).
• Start the entire process again to detect the ESU noise

Whenever noise is there, the inventors of this invention found that the numeric value is erratic & there is no point in displaying on the TFT-LCD 116. Under this situation, the 332- SOMwill instruct a logic circuit on the motherboard to hold the previous legible numeric value (For example 524, 516, 536) for first 10 seconds. After the lapse of this predetermined time again the 332- SOM will check for digital high signal due to excess RF noise at 502.

If the noise situation continues then 502 will further digitally instruct 332 to further hold the numeric values of ECG signal being displayed on 116. Whenever the real time numeric values of heart rate extracted from ECG signal are withheld, the location of numeric value of heart rate (516) cannot be left blank. The 332 will take the previous stable value of the heart rate & display it on the 116.The part 506 is a communication link between 332 & 116. This can be LVDS, TTL type communication comprising graphic card, Graphical user interface and the like.

The reason is, for a intervinist or surgeon ( during intra surgical physiological monitoring ) the stable value of the heart rate is the most important vital sign compared to the dynamically changing & now corrupted ECG waveform, Also for trend recording of the heart rate, only numeric value is considered & reviewed later on by the caregiver.

The invention disclosed above will solve the problem of displaying stable numeric value for instant reference as well as for trend recording.

The embodiment disclosed above is by way of an example for ECG signal. But similar method & device can be implemented for other physiological signals comprising pulse oximeter, respiration detection by impedance plethesmography, human body temperature, invasive blood pressure, capnography and the like.

Although the above disclosed test set in Fig 1 & Fig 2 is used for testing spo2-pulse oximeter & ECG-electrocardiographic parameters the same setup can be used without substantially deviating for testing other sensors, transducers& patient interface cables used for acquiring physiological parameters.

By way of an example the following tests can be performed

a) The various patient plates 124 ,220,208,210 can be checked for performance tests, adhesiveness, effectiveness of contact with human skin surface , useful life of electrode 124 under worst field conditions.

b) The invasive blood pressure transducer which is inserted into the radial artery for measuring invasive blood pressure cab be dipped inside the saline solution 128 like 106 & 108 to test the performance

c) The EEG (Electroencephalogram) electrodes used for monitoring brain functioning can be placed similar way of 202,204,212 and checked for noise absorption through a patient interface cable similar to 206,214,218.

d) Instead of using tip of the electrode 130 ( Fig 1) to generate spark, the various part of the cable 112,104 can be dipped inside the saline solution 128 to test the insulation strength or Hi-Pot test. If insulation is weak or punctured then a current will pass through 128 which can be detected on 116.

e) Ground bonding & integrity test for the return electrodes 124 & 220

f) Patient Leakage current, Patient to earth leakage current flowing through 104 when the generator 102 is switched OFF.

The detailed front panel display 116 in Fig 5 discloses more information on this.

Part 508 is an alarm symbol displayed to caregiver whenever the ESU-DET signal is high and remains so for say for around 10 seconds so that the real time physiological parameters of the patients are not neglected for prolonged time.

Part 510 is the name of the patient for whom the trend values of the physiological parameters are stored.

Part 512 is electro-cardio waveform acquired through 202,204& 212 hydrogel electrodes.

Part 514 is electro-cardio waveform acquired through 202,204 & 212 hydrogel electrodes but depicted in different manner.

Whenever 102 is activated these waveforms will be corrupted due to noise interference.

Part 516 is numeric value- beats per minute (bpm) of the ECGwaveform 512 & 514 which is also called HR (Heart rate). Since this value is most significant to an anesthesiologist or intervenist to control the flow of anesthesia gases, the values are shown in substantially larger font size compared to other parameters. There is a requirement that this value should not be erratic.

Part 518 indicates the type of filter cut off frequency selected in Part 300, Fig 3. The noise from 102 can also be eliminated by changing the bandwidth of the filter. This is done by changing the value of the capacitors & resistors which in turn is done by electronically switching. This contains three options. Diagnostics mode, monitoring mode, OT mode

The diagnostic mode is wide band width mode where the signals acquired by 202,204,212 are least filtered by the circuits disclosed in Fig 3. This is used before the surgery to get a detailed heart condition of the patient. This mode is also used on a healthy person to study the heart functions.The monitor & OT mode are used during surgery where the band width of the filters as shown in Fig 3, Part 300 is severely limited to cutoff the noise in most of the situations. An audible message, beeper alarm, visual indicator Part 540 can also be provided to alert the caregiver. Part 520 is the upper & lower limits display provided for 516 so that alarm 508,540 are activated whenever HR crosses these limits. Whenever the heart rate value at 516 crosses the limit set in 520 then, the 504 signal is not set to logical high( + 5 volt)so that 332 will display only the real time value. This is needed since the alarm 508 & 540 will ring continuously. When this occur a message "HF noise - check patient since parameters are crossed the limit set in 520" can be displayed. This will help the caregiver to personally check the patient's condition and to investigate why the parameters are crossed the limits in 520.

The part 522 is oxygenated hemoglobin -saturation waveform acquired from the sensor 108. When 102 is activated this waveform will be corrupted due to cautery noise. Part 524 is the location where the numeric value of pulse rate in is shown.

Part 526 is the display location where the higher & lower alarm limits for the value of the 524 can be set.

The part 528 is the respiration waveform which depicts the lung movement & inhale / exhale of the breathed gas. This waveform is derived by injecting a carrier frequency through 202,204 & 212 into the thoracic portion of the 110. The frequency will be around 55 kilo hertz &litude in volt, whichis modulated according to the thoracic movement of the chest portion. The part 530 is the numeric value called respiration rate or breathing frequency which is denoted by bpm(breaths per minute).

Part 534 is the higher & lower alarm limit setting for the 530 so that visual & audible alarms (540,508) can be generated

To indicate the emergency conditions, the part 532 is apnea or breathless indicator. Due to 102 activation the noise will corrupt the waveform 528 & numeric value 530. If this prolongs then the system will think that there is apnea condition if no real time value is displayed in 530. Readjusting the limits in 534 can solve this problem.

Part 536 is the skin temperature of the subject 110 which is acquired through thermistor based temperature probes. When 102 is activated for long time these values can get corrupted due to noise pickup. The filters shown in Fig 3 part 300 can also be implemented to reduce the HF noise. The setup described in Fig 1 and Fig 2 can also be used to test the noise in temperature probes. The part 538 is higher & lower alarm limit setting so that false alarm due to erratic values of 536 can be eliminated.

The machine may include a processor (e.g., a central processing unit (CPU), a graphics processing unit (GPU, or both), a main memory and a static memory, which communicate with each other via a bus. The machine may further include a video display unit (e.g., a liquid crystal display (LCD), a flat panel, a solid state display, or a cathode ray tube (CRT)). The machine may include an input device (e.g., a keyboard) or touch-sensitive screen, a cursor control device (e.g., a mouse), a disk drive unit, a signal generation device (e.g., a speaker or remote control) and a network interface device.

Figure 6 illustrates shield placement and method of shield functioning when used with spo2 sensor and circuit disclosed in Fig. to attenuate the HF surgical noise

Part 602 is metallic chassis fabricated from sheet metal and is heavily conductive so that the electrical noise, ESD (electro static discharge), eddy currents, EMI & EMC related noise are conducted to ground.

The sensor 108 with yoke 112 and connector 120 are connected to the interface panel 118 which is also shown in Fig 1. Part 332 is the motherboard which is also shown in Fig 3 & Fig 5. Part 612 is the SP02 signal acquisition board. Part 608 are spacer bushes provided at regular intervals between the sheet 610, mother board/SOM 332 so that the conductive sheet 610 will not cause electrical short circuit yet the effective shielding & noise suppression takes place.

A cable placed behind the panel 118 will connect 120 and 612. The spo2 signals from 108 are acquired by 612 and are sent to 332. The 332 will operatively communicate as shown in Fig 5 to display the waveform and numerical parameter.

It was experimented & found by the inventors of this invention that by placing plastic sheets 616, 610 multi-layered with conductive metal, semi-conductive ferrite material, ferromagnetic alloys, the noise due to 102 is attenuated substantially. For additional effectiveness the sheets 616,610 can be connected by a grounding cable 614 and is grounded to the equipotential ground 606. During the extreme noise condition, the point 606 and the chassis 602 can also be grounded to an earth wire 604 buried inside the soil at distal end.

The sheets 616 & 610 are fabricated to suit the custom needs. The part 622, 620, 618 are various layers of material that can be used for effective shielding and shows the cross section of 616. By way of an example 618 can be oxygen free, highly conductive copper foil or pressure sensitive acrylic adhesive transfer tape, 620 can be plastic sheet ( polyamide/polyester) for structural support, part 622 can be ferrite particles/conductive fillers glued to the surface of 620. The part 622 can also be ethylene propylene rubber tape, polyamide, silver pigments suspended in thermoplastic resins mumetal, conductive metallized filled silicone elastomers and the like.

These sheets can also be installed inside the yoke 112 or sensor 108 to suppress the noise at originating point.

WE CLAIM:

1. An electro-surgical noise testing system for testing the electromagnetic interference on patient monitor comprising:

an electrosurgical generator, said electrosurgical generator generating power output; plurality of electrodes, sensors and cables means operatively connected to said electrosurgical generator at distal end through one or more electrical connectors for circulating high frequency current in the system;

at least one sensor means for sensing physiological parameters;

a yoke having noise filtering circuit connected to said sensor means at one side;

a display means for displaying the sensed physiological parameters;

wherein said display means comprising noise detecting and filtering circuitry to block the electromagnetic interference and display the electromagnetic interference free signal on the output display screen.

2. The system as claimed in claim 1, wherein said electrode means comprising active electrodes comprising electrosurgical knife and inactive electrodes comprising dispersive pad, immersed in the salt water for noise interference measurement.

3. The system as claimed in claim 1, additionally comprising an anticorrosive, electrically non-conductive beaker filled with salt water for electrosurgical noise interference measurement made from borax/borosilicate glass or a polycarbonate plastic beaker.

4. The system as in claim 1 where the finger sensor is connected to thumb and rest of the fingers immersed inside the said saline/salt solution and connected to patient monitor so that noise and the useful signal reach the said monitor to display the said noise and signal on TFT display.

5. The system as in claim 1 containing activated electrosurgical generator injecting current through patient's body using plurality of dispersive electrodes, surgical pencil and cables so that the noise is picked up by the ECG electrodes and leads, yoke and connector and further by the patient monitor in second embodiment.

6. A method for detecting and suppressing the electromagnetic interference comprising the steps of:

a. Filtering an input signal received from a yoke by filter means and allowing the ECG signal to reach the motherboard and displaying as it is when there is no noise.

b. Checking for noise signal in ECG and amplifying and separating the noise using high pass filter means , buffering, isolating using linear optical isolator so that ESU-DET signal is provided for PIC controller.

c. Allowing the PIC controller to make decision about whether to make CAUTDET output high and the duration for which this signal to be high so that the motherboard will display the previous legible and stable value on the output display.

d. Allowing the motherboard to make the decision on whether to show the real time physiological parameters as it is, when there is no noise interference or the value of the said parameters 516 crossing the high and low limit ( 520) so that the alarms 508 and 540 are not inadvertently activated during the noise.

e. Allowing the said motherboard to make decision on further displaying the previous legible value for next 10 seconds or more whenever noise is detected and the value to be displayed at 516 is within the set limit of 520

7. The system as claimed in claim 1 comprising noise absorbent means.

8. The system as claimed in claim 7 wherein said noise absorbent means is made of multi-layered plastic sheets having various electrically conductive, ferrite, semi-conductive material used behind the patient interface connector panel, beneath the spo2 signal acquisition module.

9. The system as claimed in claim 8, wherein said noise suppressing sheets being inter-connected with highly conductive grounding cable and soldered to metal chassis of the said patient monitor so that there will be a provision to pass all the noise, ESD charges, surges to the mother earth by means of earth cable

10. The method as claimed in claim 6 wherein the noise is absorbed by noise absorbent means made of multi-layered plastic sheets having various electrically conductive, ferrite, semi-conductive material used behind the patient interface connector panel, beneath the spo2 signal acquisition module.