a perforation detection system 10 ( also referred to as a “ body cavity assessment system ”) utilizing principles of the present invention will be described herein as forming part of an rf ablation system used to ablate tissue within a body cavity such as a uterus . however , it should be appreciated that the perforation detection system 10 may be provided with another type of system used for treatment , or it may be provided independently of a larger treatment system . generally speaking , perforation detection system 10 includes a medical ablation device 12 of a type used for tissue ablation , and an rf generator system 14 of the type used to deliver rf ablation energy to an electrode array on ablation device 12 . the rf generator unit , however , is provided with additional components that are used for the body cavity assessment function of the present invention . in particular , the rf generator unit is provided with a fluid / gas source 16 and a body cavity assessment interlock 20 . fluid / gas source 16 is fluidly coupled to ablation device 12 via a source line 22 . the ablation device is positionable within a body cavity bc so as to deliver fluid / gas from source 16 through the source line 22 and the ablation device and into the body cavity . body cavity assessment interlock 20 includes a pressure sensing system 24 fluidly coupled to the medical device via pressure detection / signal line 26 . pressure sensing system 24 monitors the pressure within the body cavity bc while fluid / gas is being ( or after it has been ) delivered to the body cavity , and detects whether elevated pressure can be maintained over a predetermined period of time , within a predetermined window of time . if it cannot , the user is alerted that there may be a perforation in the organ . body cavity assessment interlock 20 further includes an interlock system 28 that prevents treatment with the ablation device 12 unless body cavity assessment has been performed . the rf generator system 14 is additionally provided with a vacuum system 30 coupled to pressure detection / signal line 26 , rf circuitry 27 , and other components needed to perform the ablation function . a footswitch 32 or other input device controls operation of the rf generator system 14 . a microprocessor or programmable logic device 34 within the rf generator system 14 governs various functions , including the body cavity assessment , interlock , and rf ablation procedures . an example of an rf ablation device 12 that may be used with the system 10 is shown in fig2 a and 2b . ablation devices of this type are shown and described in u . s . pat . no . 5 , 769 , 880 and u . s . application ser . no . 09 / 103 , 072 , each of which are incorporated herein by reference . a similar device is the novasure ablation device available from novacept , inc ., palo alto , calif . naturally the perforation detection system may be provided in combination with the other medical devices as well such alternative devices include thermal ablation devices in which heated liquid is circulated through a balloon positioned within the body cavity of interest , or other device used for procedures besides ablation . alternatively , the system may be provided with two medical devices , one for use in delivering inflation medium and another for use in treating body tissue . as a further alternative , a treatment device may be provided independent of the system 10 . ablation device 12 is configured to deliver rf ablation energy to the interior surface of a body cavity , while causing moisture ( e . g . steam ) generated during ablation to be withdrawn away from the body tissue — preferably using suction . this moisture transport feature of the device 12 is advantageous in that removing steam from the ablation site minimizes the amount of thermal ablation would otherwise be caused by the steam . greater control over ablation depth is thus achieved by allowing ablation to occur only ( or primarily ) by rf energy rather than by thermal conduction . the device 12 includes an rf applicator head 36 , a sheath 38 , and a handle 40 . the applicator head 36 is slidably disposed within the sheath 38 to give the applicator head 36 a streamlined profile ( fig2 a ) to facilitate insertion of the device into a body cavity ( e . g . the uterine cavity ). once the applicator head 36 has been inserted into the body cavity , handle 40 is manipulated to cause the applicator head 36 to extend from the distal end of the sheath 38 and to expand into the position shown in fig2 a as to make contact with body tissue . referring to fig2 b , in which the sheath 38 is not shown for clarity , applicator head 36 extends from the distal end of a length of tubing 42 which is slidably disposed within the sheath 38 . applicator head 36 includes an external electrode array 44 and an internal deflecting mechanism 46 used to expand and tension the array for positioning into contact with the tissue . the array 44 is preferably formed of a stretchable metallized fabric mesh which is preferably knitted from a nylon and spandex knit plated with gold or other conductive material . in one array design , the knit is formed of three monofilaments of nylon knitted together with single yarns of spandex . each yarn of spandex has a double helix of five nylon monofilaments coiled around it . when in its expanded state , the array 44 includes a pair of broad faces 48 ( one of which is shown in fig2 b ) spaced apart from one another , and narrower side faces ( not shown ) extending between the broad faces 48 along the sides and distal end of the applicator head 36 , and a distal face 52 extends between the broad faces 48 at the distal end of the applicator head 36 . insulating regions ( not shown ) formed by etching other techniques on the applicator head to divide the mesh into electrode regions . the array may be divided by the insulated regions into a variety of electrode configurations . in a preferred configuration the insulating regions divide the applicator head into four electrodes by creating two electrodes on each of the broad faces . deflecting mechanism 46 and its deployment structure is enclosed within electrode array 44 . external hypotube 58 extends from tubing 42 and an internal hypotube 60 is slidably and co - axially disposed within hypotube 58 . flexures 62 extend from the tubing 42 on opposite sides of external hypotube 58 . hypotube 60 is a dual lumen tube that is coupled to the pneumatic subsystem as will be described below . a plurality of longitudinally spaced apertures ( not shown ) are formed in each flexure 62 . during use , these apertures allow moisture to pass through the flexures and to be drawn into exposed distal end of hypotube 58 using a vacuum source located in the rf generator system 14 and fluidly coupled to hypotube 58 . each flexure 62 preferably includes conductive regions that are electrically coupled to the array 44 for delivery of rf energy to the body tissue . for example , strips of copper tape ( not shown ) or other conductive material may extend along opposite surfaces of each flexure . conductor leads ( not shown ) are electrically coupled to the strips and extend through tubing 42 to an electrical cable which is attachable to the rf generator . during use , one conductive strip on each conductor is electrically coupled via the conductor leads to one terminal on the rf generator while the other strip is electrically coupled to the opposite terminal , thus causing the array on the applicator head to have regions of alternating positive and negative polarity . it is important to ensure proper alignment between the conductive regions of the flexures ( e . g . the copper strips ) and the electrodes in order to maintain electrical contact between the two . strands of thread ( which may be nylon ) are preferably sewn through the array and around the flexures in order to prevent the conductive regions from slipping out of alignment with the electrodes . during use of the ablation device , the applicator head 36 is inserted into the uterus with the sheath 38 covering the array 44 to compress the applicator head 44 into a streamlined condition . once the applicator head is within the uterus , the handle is used to withdraw the sheath and to open the array into its deployed position . vacuum source 30 ( fig1 ) is activated , causing application of suction to hypotube 60 . suction helps to draw uterine tissue into contact with the array 44 . ablation power is supplied to the electrode array 44 by the rf generator system 14 . the tissue is heated as the rf energy passes from electrodes 56 a - d to the tissue , causing moisture to be released from the tissue . the vacuum source helps to draw moisture from the uterine cavity into the hypotube 60 . moisture withdrawal is facilitated by the apertures formed in flexures , by preventing moisture from being trapped between the flexures and the lateral walls of the uterus . the fluid / gas source 16 , pressure sensing system 24 , and associated components are shown in fig3 . each of the components of the pressure sensing system 24 is preferably coupled to microprocessor 34 of the rf generator system 14 although for clarity the microprocessor is not shown in fig3 . all pressure transducers , solenoid valves , and the vacuum pump are controlled by the microprocessor . it is also important to note that in the embodiment described below the roles of the two lines ( source line 22 and pressure detection / signal line 26 ) play different roles during rf ablation than for perforation detection . specifically , the signal line 26 for perforation detection serves as a suction line for ablation . the source line 22 for perforation serves as a vacuum signal line for ablation . components along the source line 22 will first be described . fluid / gas source 16 is preferably a disposable co 2 cylinder , and may be a 16 gm cylinder providing approximately 850 psi at 25 c . one such example is the linde medical grade 16 gm cylinder . the cylinder is removably attached to a pressure regulator 68 such as the leland model 50033 or equivalent . regulator 68 includes a main shutoff valve 70 and pressure regulation component 72 which has a control pressure of approximately 60 psi . a pressure gauge 74 such as sensym model ascx100dn or equivalent is fluidly coupled to source line 22 . pressure gauge 74 monitors the pressure remaining in the fluid / gas source 16 so as to detect when a low volume of fluid / gas remains , or when the user has failed to open the valve 68 . a solenoid valve 76 is positioned along the source line 22 , downstream of the pressure regulator 68 . valve 76 remains in a closed condition , preventing flow of gas through the line 22 , except when a cavity assessment procedure is being carried out . a second pressure regulator 78 , such as an airtrol r - 920 series regulator , is positioned downstream of the valve 76 so as to reduce pressure in line 22 down to approximately 90 +/− 10 mmhg during a cavity assessment procedure . a flow control orifice 80 , positioned downstream of regulator 78 , limits flow in line 14 to 100 +/− 10 scc / min ( standard cc / min ). a pressure sensor upstream of orifice 80 monitors whether the pressure limit ( of , for example , approximately 100 mm hg ) has been exceeded . if the limit has been exceeded , an output signal from this sensor causes an audible alarm to be triggered and the solenoid valve 76 is turned off . downstream of orifice 80 , source line 22 is coupled , using a flexible tygon tubing for example , to the introducer sheath 38 ( fig2 b ) of the ablation device 12 . the introducer sheath is located at the internal surface of the body cavity bc ( the internal os , for example , in the case of a uterine cavity ) so as to deliver gas into the body cavity bc that is to be treated . turning to the components along the pressure detection line 26 , the pressure signal line 26 is fluidly coupled , using a tygon tubing for example , to the lumen of hypotube 60 . downstream of the medical device 12 is a pressure sensor 84 , such as the sensym acsx05dn . during a cavity assessment procedure , sensor 84 monitors pressure in the pressure signal line 26 and delivers the signal to microprocessor 34 . microprocessor 34 then determines if pressure in the body cavity bc has failed to achieve a predetermined threshold ( indicating a perforation in the body cavity ) or if it has and maintained the threshold for a predetermined time period ( indicating that the body cavity has no perforation ). further downstream of the pressure sensor 84 is a vacuum pump 86 . while not needed for perforation detection , vacuum pump 86 is used to carry out the moisture transport function of the medical device 12 described in the section entitled ablation device above . a second solenoid valve 88 lies upstream of the vacuum pump 86 . valve 88 remains open at all times except during cavity assessment . because the exhaust line of the vacuum pump may not be air - tight when it is not operating ( including during the cavity assessment procedure ) the valve 88 is provided to close the pressure signal line against leaks through the vacuum pump . a simplified state diagram illustrating operation of the system is shown in fig4 . operation begins with valve 76 in the closed condition , and with valve 88 in the opened condition . in preparation for use of the system , a co2 cylinder 16 is connected to the appropriate receiving device on the rf generator &# 39 ; s pneumatic subsystem ( fig3 ). the power to the generator is switched on . pressure gauge 74 detects the pressure in the portion of pressure / monitoring line 22 extending between co 2 cylinder 16 and valve 76 . if the user has failed to open the main co 2 shutoff valve 70 , or if the pressure detected by gauge 74 is less than the specified pressure , an audible alert will sound , indicating a low - gas condition . assuming no low - gas condition is detected , the user will connect the ablation device 12 to the . rf generator system 14 . the system remains in a “ wait for connect ” condition , step 102 , until the user connects the ablation device 12 to the rf generator system . when the ablation device is plugged in , it actuates a microswitch or similar feature , which alerts the microprocessor that the ablation device has been connected . connection of the device automatically starts the “ co2 purge ” cycle , step 104 . during the purge cycle , valve 76 is opened to permit the flow of co 2 through the device to drive air from the device . the purge cycle lasts for a duration sufficient to purge the air from the system , approximately 10 seconds . during the purging cycle the user is alerted by audible and visual indicators not to insert the device into the body cavity in order to prevent air from being delivered into the body . as a safety precaution , the vacuum pump that is part of the rf controller is pulsed every few seconds during purging . if the user has inserted the ablation device into a body cavity during purging , the vacuum pump will draw out air that is delivered to the body . during the purge cycle and device insertion into the body cavity , the ablation device is closed , such that the poles of the electrode array are in contact with each other . a low voltage signal is applied to the ablation device which senses that the poles are in contact by detecting a dc short . after the completion of the purging cycle the system waits for the device to be deployed within the patient , step 106 , by monitoring for the end of the dc short condition . once the user inserts the device into the uterine cavity and opens the array , the system detects that a dc short condition is no longer present . as a safety precaution , the perforation detection cycle cannot be initiated until the dc short condition is eliminated . in this way the last operation to be performed before the application of rf energy is the perforation detection cycle . from the completion of the purge cycle to the initiation of the perforation detection test , a continuous , low level flow of co2 is circulated through the ablation device to keep the source and pressure signal lines open and free from blockage . next , the system waits for the user to depress the footswitch 32 , “ wait for footswitch ”, step 108 . once the footswitch has been depressed , a 30 - second timer is initialized (“ reset timer ”) and the perforation detection test , (“ perform pressure test ”) 110 begins . valve 88 is energized to close off the vacuum pump 86 to avoid loss of pressure through it . if it was not already opened , valve 76 is opened , allowing co 2 to flow into the body cavity via medical device 12 . when the pressure at gauge 84 rises and remains above 50 mmhg for 4 seconds , the test has passed and the system moves to a “ passthrough ” state . ( it should be noted that the system may alternatively pressurize the cavity and then detect whether the monitored pressure falls below a predetermined level within a predetermined time period , indicating that a perforation may be present .) in the “ passthrough ” condition the co 2 is turned off and the vacuum pump is re - enabled by re - opening valve 88 . if the enable button 33 has been pressed ( automatic mode ), rf power 114 (“ apply rf power ”) will be delivered automatically to the array 44 once the cavity assessment cycle has been completed and passed . if the enable button has not been depressed ( semiautomatic mode ), the system moves through the “ passthrough ” state and waits for footswitch actuation 112 (“ wait for footswitch ”). the user must press the button to enable the rf generator and then press the foot switch 32 to deliver rf power 114 . in the event the cavity assessment test is not passed after the 30 second timer has expired , an audible tone sounds and visual indicators flash . the system remains in a test fail state , step 116 , and awaits further action by the user . if the user presses the foot switch , the system is re - sets to the initial ready state , step 108 , with the co 2 flow off . the user may attempt the cavity assessment sequence as many times as desired . alternatively , after one or more cavity assessment procedures has been performed and failed , the user may choose to override the system and cause the system to deliver rf energy despite the cavity assessment test having been failed . to do so , the user will press and hold the enable button 33 for six seconds . note that the pressure check must be attempted at least one time before this feature is available . if the user overrides the cavity assessment , the system moves to the “ passthrough ” state to wait for footswitch step 112 . if at any time during the above sequence , the user should close the ablation device , a dc short will be detected in the electrode array by the rf generator &# 39 ; s dc short detection circuitry . closing the device causes the state of the perforation test to change to fail , and the system resets to the “ wait for deploy ” state , step 106 . the system will then require that cavity assessment be performed again once the array is reopened . this assures that the last step performed before the application of rf energy is the perforation detection test : if the user , after having successfully completing the test , decides to close and remove the device for any reason , the perforation detection test must be performed again - once the device is deployed in the body cavity . this requirement also prevents a user from abusing the system by running cavity assessment with the device outside the body , and then inserting the device , overriding the test , and ablating without having every performed cavity assessment within the body cavity . for additional safety , the perforation detection system preferentially uses co2 , though other gases or liquids , such as normal saline , may be used . the pressure and flow limits follow well known guidance documents for insufflators . in the case of uterine perforation detection , the limits follow hysteroflator guidance documents . though other configurations are possible , the cavity to be assessed should be in series between the source and pressure signal lines . in this manner , any kinked tubing or other problems will not lead to a false test result . additionally , the system is capable of detecting perforations exceeding the range of sizes of devices normally inserted into body cavities ( from say 15 mm down to less than 1 mm diameter ). in order to reliably detect perforations in uterine cavities , the pressure threshold in that case is preferentially kept below the average cracking pressure of the fallopian tubes . there are several features that improve the system &# 39 ; s ease of use . firstly , the physician can start or stop the perforation test at any time in the sequence . secondly microprocessor 34 is capable of distinguishing the difference between a device that is closed versus a device that is undergoing slight motion in the body cavity , thus reducing the likelihood that a passed test condition will be overturned . finally , the system includes a collar assembly 63 in fig2 a which is capable of sealing the entry into the body cavity bc if leaks are determined to exist , thus reducing the likelihood of a false test failure . although the forgoing description is with reference to a perforation detection system having a device usable to ablate tissue within a uterus , the present invention is applicable to perforation detection within other body cavities , and to perforation detection systems having medical devices useful for procedures other than ablation . in addition , although the system is described with reference to a particular embodiment , many other configurations are suitable for implementing the teachings of the invention . those having ordinary skill in the art will certainly understand from the embodiment disclosed herein that many modifications are possible without departing from the teachings hereof . all such modifications are intended to be encompassed within the following claims .
a system and method for detecting perforations in a body cavity . in accordance with the method of the invention , a fluid is delivered into a body cavity to slightly pressurize the cavity . a pressure sensing system monitors the pressure within the cavity for a predetermined test period . if cavity pressure is not substantially sustained during the test period , the physician is alerted to further assess the cavity for perforations before initiating treatment within the cavity . in a preferred form of the system , a medical treatment system such as an rf ablation system is provided with perforation detection functionality . the system preferably includes a pre - test and post - test lockout system . the lockout system prevents rf power delivery unless , during a predetermined test period , the pressure sensing system determines that no perforation exists , or unless a previously performed perforation detection procedure determined a perforation was present but the lockout system was subsequently overridden by the physician .