referring to fig1 carbon dioxide gas is supplied at a high pressure to the insufflator from co2 reservoir 10 . this reservoir may be any size of high pressure gas cylinder intended for use with carbon dioxide . co2 reservoir 10 is connected to electronic high pressure sensor 12 , which in the preferred embodiment is a microgage model p149 , capable of sensing pressures up to 2000 psi . also connected to co2 reservoir 10 is high pressure regulator 14 , which in the preferred embodiment is a norgren model r83200rnea , which reduces the pressure of the co2 gas from co2 reservoir 10 to a pressure of 25 psi . connected to the output of high pressure regulator 14 is high pressure relief valve 16 , which opens and exhausts co2 gas if the pressure exceeds 30 psi . in the preferred embodiment , high pressure relief valve 16 is circle seal d533b - 2m - f , 30 . also connected to output of high pressure regulator 14 is electronic pressure regulator 18 , which in the preferred embodiment is a bellofram 241 - 962 - 095 - 000 . this regulator incorporates an adjustable responds to an electronic control signal to supply an output pressure ranging from 0 to 55 mmhg , and a pressure reliever which opens to bleed off gas if the outlet pressure exceeds the pressure set by the pressure reducer component . the operation of electronic pressure regulator 18 is internally controlled by an electronic pressure sensor and a control circuit . connected to the outlet of electronic pressure regulator 18 is valve 20 , which in the preferred embodiment is a normally closed valve , model 211 - a - 1 / 4 - f - br - 1 / 4 , manufactured by burkert . valve 20 is connected in turn to flow transducer 22 , ( honeywell , awm5104vc ), which provides an electronic signal proportional to flows of co2 ranging from 0 to 20 standard liters per minute ( slpm ). the outlet of flow transducer 22 is connected to relief valve 24 , pressure transducer 26 and filter 28 . in the preferred embodiment , relief valve 24 is a circle seal model 533b - 2m - b relief valve which relieves pressures above 60 mmhg . pressure transducer 26 is a sensym scx01 dn pressure sensor rated at 0 to 1 psi . filter 28 is a 0 . 3 micron electret filter element made by 3m , enclosed in a housing which is connected to the outlet of flow transducer 22 such that all gas flowing out of flow transducer 22 in normal operation must pass through filter 28 . the outlet of filter 28 is connected to the patient &# 39 ; s body cavity 30 by means of hose 32 . in the preferred embodiment , filter 28 is a custom filter element manufactured by cybermedic of denver colo ., although many other kinds of filter suitable for this application are available ( pall , gelman scientific , marquest , arbor technologies , fibretek and others ). electronic sensor signals from high pressure sensor 12 , flow transducer 22 , pressure transducer 26 and electronic regulator 18 are all connected to control circuit 34 . electronic control signals from control circuit 34 are connected to electronic regulator 18 and valve 20 . referring to fig2 control circuit 34 consists of a microprocessor circuit , many examples of which are known in the art . control circuit 34 includes analog to digital converter 36 , which converts analog voltage signals from high pressure sensor 12 , flow transducer 22 , pressure transducer 26 and electronic regulator 18 , into digital form for use by microprocessor 38 . microprocessor 38 also receives control information from switches and controls 46 , and controls the operation of valve 20 , integrator 48 , displays and indicators 44 and alarm 42 . memory 40 provides program steps and calibration settings for microprocessor 38 . integrator 48 converts the variable pulse width signal from microprocessor 38 into a variable dc voltage to control electronic regulator 18 . in operation , the connection of gas supply 10 to the insufflation device causes high pressure sensor 12 to send a signal to analog to digital converter 36 indicating the amount of co2 pressure available in gas supply 10 . microprocessor 38 causes displays and indicators 44 to indicate the amount of gas remaining . high pressure regulator 14 reduces the pressure of the co2 gas to 25 psi , which is directed to the input of electronic regulator 18 . in the event that high pressure regulator 14 fails to regulate the co2 pressure below 30 psi , relief valve 16 opens to allow the co2 gas to escape . microprocessor 38 reads switches and controls 46 to determine the desired insufflation pressure set by the user . this information , along with pressure and flow values detected by flow transducer 22 and pressure transducer 26 , is used by microprocessor 38 to establish a desired control signal value for electronic regulator 18 . microprocessor 38 does this by sending a rapidly repeating pulse to integrator 48 , the pulse width of which is calculated to cause integrator 48 to generate the desired control signal value for electronic regulator 18 . this technique , widely known in the art as pulse width modulation ( pwm ) permits microprocessor 38 to synthesize a continuous analog voltage from a digital ( two state ) output signal . the software program stored in memory 40 controls the operation of microprocessor 38 . the program algorithm used to determine the desired control signal value for electronic regulator 18 is a proportional integral derivative ( pid ) function which responds to the pressure values detected with pressure transducer 26 . the output of the pid algorithm is further modified in response to the signal from flow transducer 22 . if the flow rate measured by flow transducer 22 exceeds the maximum flow rate set by the user , microprocessor 38 decreases the output of electronic pressure regulator 18 to reduce the flow to acceptable levels . the software program in memory 40 also causes microprocessor 38 to detect various abnormal conditions . one such condition is a leakage of gas from the patient &# 39 ; s body cavity at a rate too high to be replenished by the insufflator this condition is considered to exist if microprocessor 38 fails to detect any increase in pressure sensed by pressure transducer 26 while the flow sensed by flow transducer 22 is at or near the maximum flow rate set by the user . if this condition continues for a set period of time , microprocessor 38 turns on one of displays and indicators 44 and alarm 42 to indicate a leak . microprocessor 38 also detects and warns of kinks in the hosing between the insufflator and the body cavity . to determine the existence of this condition , the output of electronic regulator 18 is increased for a short period of time . if pressure transducer 26 detects a very rapid increase in pressure , indicative of a very small volume connected to the outlet of electronic pressure regulator 18 , a kink condition is deemed to exist . this condition is indicated on displays and indicators 44 and with alarm 42 . excessive pressure in the patient &# 39 ; s body cavity for any reason is immediately sensed by pressure transducer 26 . if this pressure exceeds 30 mmhg at any time , microprocessor 38 immediately indicates this condition with displays and indicators 44 and alarm 42 . in addition , microprocessor 38 will indicate an over pressure alarm if the pid control function is unable to cause the pressure sensed by pressure transducer 26 to return to within 3 mmhg of the pressure selected by the user within a fixed time period . as an additional check on the function of electronic regulator 18 , a signal from electronic regulator 18 , representative of the pressure detected by its internal pressure sensor , is directed through analog to digital converter 36 , to microprocessor 38 . this signal is also used by microprocessor 38 to check the function of pressure transducer 26 . the gas output of electronic regulator 18 is directed into normally closed valve 20 . this valve is selected to close off the supply of gas to the patient &# 39 ; s body in the event of a power failure or other failure of the insufflator . valve 20 can also be closed by microprocessor 38 so that the actual pressure in the patient &# 39 ; s body cavity can be checked with pressure transducer 26 at any time . also connected to analog to digital converter 36 are signals from flow transducer 22 and pressure transducer 26 . these signals are converted to digital form and directed to microprocessor 38 , so that microprocessor 38 can monitor the flow rate of gas to the patient and measure the insufflation pressure being used at any time . connected to the outlet of flow transducer 22 is relief valve 24 , which will open and exhaust gas if the pressure exceeds 60 mmhg . this valve is intended to act as a safety relief in the event that pressure in the patient &# 39 ; s body cavity exceeds this pressure for any reason . displays and indicators 44 are controlled by microprocessor 38 to display information which may be useful to the surgeon , including the insufflation pressure , the actual abdominal pressure , the flow rate of gas into the patient , the total volume of gas insufflated , and the total insufflation time . alarm 42 may be turned on by microprocessor 38 in the event that the insufflation pressure exceeds a set value , if leaks or occlusions in insufflation hose 32 occur , or if the supply of gas in co2 reservoir 10 falls below a minimum acceptable level . referring to fig3 insufflator 50 is typically connected to gas supply 10 with high pressure hose 52 . filter 28 is connected to insufflator 50 and to insufflation hose 32 , which is connected in turn to patient &# 39 ; s body cavity 30 through trocar 54 . typically , filter 28 and insufflation hose 32 are constructed of inexpensive , stedle material which may be disposed of after each surgical procedure . in use , the surgeon uses switches and controls 46 to set the desired pressure in the patient &# 39 ; s body cavity and the maximum allowable gas flow rate , and then begin the insufflation . displays and indicators 44 continuously display the pressure in the body cavity , the flow rate , time and other information useful to the surgeon . many adaptations and variations to the present invention are possible , accordingly , the invention is to be limited only by reference to the appended claims . for example , although the preferred embodiment described is intended for use with carbon dioxide gas , other gasses such as helium or nitrous oxide may be used . various means for controlling the flow of gas so as to allow relief of pressure above the desired pressure can be contrived . although the filter used in the preferred embodiment is a 0 . 3 micron electret type , filter means of various pore sizes and types could be used to remove particles of various sizes .
the flow of insufflating gas is adjustable and regulated to prevent excessive pressure in the body cavity . a filter removes particulate matter from the gas entering the body and removes bacterial and viral matter from the gas leaving the body cavity .