as shown in the drawings for the purposes of illustration , the present invention is embodied in a thermal balloon ablation apparatus which comprises a reusable component and a disposable component for delivering therapy to a body cavity . in accordance with the present invention as shown in fig1 a and fig1 b , the thermal balloon ablation apparatus comprises a reusable component 2 and a disposable component 4 . reusable component 2 further comprises a housing 6 which has a handle 8 . integral to housing 6 is a display means 10 and user controls 12 . disposable component 4 comprises a distal balloon 14 , a semi - rigid or rigid catheter 16 having a distal and proximal end , a semi - rigid or rigid distal sheath 18 , a flange 20 , a semi - rigid or rigid proximal sheath 22 , a pneumatic fitting 24 , a proximal balloon 26 , and a protective shield 28 . fig2 shows a detailed cross sectional view of disposable component 4 . distal balloon 14 can be inflated to volumes of 30 ml without generating significant back - pressure and is suitable for use at temperatures in excess of 165 c . in the preferred embodiment the balloon is fabricated from 0 . 12 mm thick silicone rubber , is shaped in the approximate shape of the uterine cavity and has a natural volume of approximately 15 ml , however other materials and shapes are acceptable so long as they allow the balloon to substantially conform to the uterus when inflated and provided they facilitate transfer of heat energy between the liquid contained in the balloon and the endometrium . distal balloon 14 is bonded in a liquid tight manner to the distal end of catheter 16 . in the preferred embodiment this bond is made using an adhesive material . the distal end of catheter 16 further includes a plurality of liquid ports 30 located such that they are contained within distal balloon 14 . in the preferred embodiment , proximal balloon 26 is fabricated from silicone rubber and has a natural volume of approximately 30 ml . the proximal end of catheter 16 is bonded in a liquid tight manner to the proximal balloon such that a liquid tight system exists comprising distal balloon 14 , catheter 16 and proximal balloon 26 . in the preferred embodiment this bond is made using an adhesive material . the liquid tight system comprising distal balloon 14 , catheter 16 and proximal balloon 26 is filled with liquid 32 such that there exists only liquid 32 within the system and no significant volume of gas at room temperature and ambient pressure . liquid 32 must be non - toxic and pose minimal hazard to the patient in the event that distal balloon 14 ruptures . ideally , liquid 32 should be such that it can be heated to temperatures above 100 c without boiling . in the preferred embodiment 100 % glycerin is used which can be heated to temperatures above 165 c without boiling at ambient pressures . a total volume of approximately 30 ml of liquid 32 is contained within the system such that the entire volume of liquid can be contained within the natural volume of the proximal balloon 26 such that distal balloon 14 can be collapsed for insertion through the cervix . the distal end of catheter 16 further includes an end cap 34 fabricated from a soft rubber material in order to reduce the risk of perforating distal balloon 14 or uterine tissue during insertion into the uterus . a thermal insulating material 36 is located between catheter 16 and distal sheath 18 and between catheter 16 and proximal sheath 22 . thermal insulating material 36 prevents excessive heating of the external surfaces of the distal sheath 18 and proximal sheath 22 during thermal balloon ablation treatment using the apparatus . in the case of distal sheath 18 , it is desirable to ensure that the temperature of the external surface does not exceed 49 c in order to prevent necrosis of tissues of the cervical canal , defined as the area between the internal opening ( also known as “ os ”) of the cervix and the external os of the cervix of a patient . in the preferred embodiment , thermal insulating material 36 is a combination of mica and closed cell silicone rubber foam . distal sheath 18 has a diameter of approximately 6 mm such that it can be easily inserted through the cervical canal of a patient . distal sheath 18 and proximal sheath 22 are separated by flange 20 which is of sufficient diameter that it cannot be inserted into the cervical canal of a patient . in the preferred embodiment , flange 20 is fabricated from silicone rubber and has a diameter of 12 mm . the dimensions of disposable component 4 are intended such that the distal end of the apparatus can be inserted through the cervical opening into the uterus to the point at which flange 20 prevents further insertion , to treat uteri with sounded depths between 7 cm and 12 cm as measured from the external cervical opening . therefore the length of distal sheath 18 plus the length of catheter 16 protruding distally beyond distal sheath 18 is less than 7 cm . the dimensions of disposable component 4 are also intended to shield the cervical canal from treatment where the cervical canal is defined , for the purpose of this embodiment , as the 3 . 5 cm long region immediately internal to the external cervical opening , and therefore distal sheath 18 is approximately 3 . 5 cm in length . it will be obvious to one skilled in the art that these dimensions can be varied to suit the anatomy of the body cavity which is to be treated using the apparatus . proximal balloon 26 is covered by a protective shield 28 comprised of a rigid heat conducting material . in the preferred embodiment , this material is thin - walled aluminum with an outer diameter of approximately 2 cm and a length of approximately 10 cm . any similar material or configuration is acceptable so long as it provides mechanical protection for proximal balloon 26 during handling and insertion into reusable component 2 and so long as proximal balloon 26 makes substantial contact with the inside surface of protective shield 28 when the total volume of liquid 32 is substantially contained within proximal balloon 26 . protective shield 28 is affixed to the proximal side of pneumatic fitting 24 . catheter 16 extends through pneumatic fitting 24 in an airtight manner . pneumatic fitting 24 further includes a rubber o - ring 38 on its proximal surface . it is necessary that all components of the apparatus which may come into contact with the vaginal canal , cervix or uterus be sterile at the time of use , non - toxic , and non - allergenic . it is intended that disposable component 4 is sterile and will be discarded after each use of the device to treat a single patient . fig3 shows a detailed cross sectional view of the pneumatic chamber 40 and associated components of the distal end of reusable component 2 . pneumatic chamber 40 further contains a cylindrical heating element 42 and an inner chamber 44 . in the preferred embodiment , heating element 42 is a 60 watt , electrically powered , flexible membrane type heater . inner chamber 44 is cylindrical in shape and approximately 2 cm in diameter and 11 cm in length such that is allows insertion of protective shield 28 and the proximal balloon 26 and liquid 32 contained therein . in the preferred embodiment pneumatic chamber 40 is fabricated from nylon material and inner chamber 44 is fabricated from stainless steel . heating insulation 46 located around the outside of the heating element minimizes heat transfer from heating element 42 to the external surface of pneumatic chamber 40 and housing 6 . a plurality of heater temperature sensors 48 are located on or adjacent to heating element 42 in order to produce a signal indicative of the temperature of heating element 42 . a plurality of liquid temperature sensors 50 are located so as to be adjacent to proximal balloon 26 when it is located in pneumatic chamber 40 and substantially filled with liquid 32 in order to produce a signal indicative of the temperature of the liquid in proximal balloon 26 . in the preferred embodiment heater temperature sensors 48 and liquid temperature sensors 50 are t - type thermocouples . pneumatic chamber 40 is connected in an airtight manner to a pneumatic pressurizing means 52 . when the disposable component 4 is installed in reusable component 2 , locking connectors 54 located on the distal end of pneumatic chamber 40 engage pneumatic fitting 24 such that rubber o - ring 38 is compressed between pneumatic fitting 24 and pneumatic chamber 40 providing an air tight seal . a disposable component detection means 55 is located on pneumatic chamber 40 and adjacent to locking connectors 54 which generates a signal when pneumatic fitting 24 is engaged on the distal end of pneumatic chamber 40 . in the preferred embodiment disposable component detection means 55 is a mechanical contact switch having an actuator which generates an electrical signal when the actuator is depressed through contact with pneumatic fitting 24 . alternately , disposable component detection means 55 can be an electrical contact mechanism and may further include an electrical fuse arrangement in disposable component 4 in which the fuse is blown by applying an electrical current from reusable component 2 after the apparatus is used to treat a patient . this allows detection of cases in which the user installs a previously used disposable component 4 in which case the apparatus could be configured to inhibit further operation . fig4 shows a detailed cross section of the proximal end of disposable component 4 assembled within and reusable component 2 . when installed in this manner , proximal balloon 26 is sealed within pneumatic chamber 40 in an air - tight manner . by modulating the pressure in pneumatic chamber 40 using pneumatic pressurizing means 52 the apparatus initiates flow of liquid 32 between proximal balloon 26 and distal balloon 14 through catheter 16 and liquid ports 30 . for example , if a vacuum of − 100 mmhg is maintained in pneumatic chamber 40 relative to ambient pressure , liquid 32 will be drawn from distal balloon 14 such that after a short period of time , substantially all of liquid 32 will be located in proximal balloon 26 . also for example , if a positive pressure of 180 mmhg is maintained in pneumatic chamber 40 relative to ambient pressure , liquid 32 will tend to flow from proximal balloon 26 into distal balloon 14 . in this case , and when distal balloon 14 is located within an enclosed cavity such as the uterus of a patient , and when this enclosed cavity is less than 30 ml in volume , after a short period of time distal balloon 14 will reach a steady state in which a volume of liquid 32 is located in distal balloon 14 with a liquid pressure of 180 mmhg relative to ambient pressure . fig5 provides details of the preferred embodiment of pneumatic pressurizing means 52 . in the preferred embodiment , pneumatic pressurizing means 52 comprises a solenoid activated 2 - way , 2 - position valve 56 , a solenoid activated 4 - way , 2 - position valve 58 , a pneumatic pressure transducer 60 , a pneumatic pump 62 and flexible pneumatic tubing 64 . the configuration shown in fig5 allows pneumatic pressurizing means 52 to generate either positive or negative pneumatic pressure at an input port of 2 - way , 2 - position valve 56 by switching 4 - way , 2 - position valve 58 and operating pneumatic pump 62 . the 2 - way , 2 - position valve 56 is switched to either connect pneumatic chamber 40 to this input port or alternately to connect pneumatic chamber 40 directly to atmosphere for rapid venting of air within pneumatic chamber 40 . pressure transducer 60 provides an output signal indicative of the pressure within pneumatic chamber 40 relative to ambient pressure and must be capable of measuring both positive and negative pressures . pneumatic pump 62 is capable of start - up and operating over a range of pressures of at least − 100 mmhg to + 180 mmhg relative to ambient pressure . it will be understood by one skilled in the art that a variety of apparatus could be similarly utilized in order to act as pneumatic pressurizing means 52 . fig6 shows details of the control system contained within reusable component 2 . re - usable component further comprises a microcontroller 66 with an integral timer 68 , and an electrical power supply 70 . in the preferred embodiment , display means 10 is an lcd module and user controls 12 comprise an on / off power switch 72 and an inflate switch 74 . microcontroller 66 accepts as inputs signals from heater temperature sensors 48 , liquid temperature sensors 50 , disposable component detection means 55 , pressure transducer 60 , and inflate switch 74 . microcontroller 66 has outputs which control operation of heating element 42 , pneumatic pressurizing means 52 and display means 10 . on / off power switch 72 provides a means for an operator to connect or disconnect microcontroller 66 and thereby all electrical components of the invention from electrical power supply 70 and thereby initiate or terminate operation of the apparatus . in the preferred embodiment , microcontroller 66 operates to control operation of the system to allow a user to deliver thermal balloon ablation treatment to the uterine cavity of a patient . the user first activates the device by turning on - off power switch 72 to the “ on ” position . this provides power to microcontroller 66 which in turn provides power as required to all electrical components of the invention and initiates the software program which is resident in microcontroller 66 . microcontroller 66 first acts to poll disposable component detection means 55 to determine if a disposable component 4 has been properly inserted and locked into reusable component 2 . if no disposable component 4 is detected , microcontroller issues a notice to the user via display means 10 and continues to poll disposable component detection means 55 . when a disposable component 4 is detected , operation of microcontroller 66 proceeds to pre - heat liquid 32 . pre - heating liquid 32 involves the following steps . first pneumatic pressurizing means 52 is activated to draw and maintain a pneumatic pressure of approximately − 100 mmhg relative to atmosphere in pneumatic chamber 40 . this has the effect of drawing substantially all of liquid 32 into proximal balloon 26 which is sealed inside pneumatic chamber 40 . then , after a period of approximately 30 seconds , microcontroller activates heating element 42 and monitors the signals from heater temperature sensors 48 and liquid temperature sensors 50 . a pressure of approximately − 100 mmhg is maintained in pneumatic chamber 40 throughout the pre - heating of liquid 32 . in the event that the temperature of heating element 42 exceeds 200 c as indicated by heater temperature sensors 48 , microcontroller turns heating element 42 off until the measured heater temperature drops below 165 c . this is to prevent excessive temperatures at the surface of heating element 42 from damaging proximal balloon 26 . pre - heating of the liquid is terminated when liquid temperature sensors 50 indicate that liquid 32 within proximal balloon 26 reaches a temperature of 165 c . in practice , pre - heating of liquid 32 typically requires about 5 minutes . during this pre - heating period , microcontroller 66 implements test routines in order to detect leaks or problems with the apparatus and proceeds to generate warnings to the user via user display 10 or inhibit further operation as warranted . these are not described but will be apparent to those skilled in the art . when pre - heating is terminated , the invention is ready for use to treat a patient . when the invention is ready for use to treat a patient , microcontroller 66 outputs a suitable message via display means 10 . microcontroller 66 then operates pneumatic pressurizing means 52 to maintain a pressure of approximately − 100 mmhg in pneumatic chamber 40 and operates to maintain liquid 32 within proximal balloon 26 at a temperature between 160 c and 170 c . maintaining the temperature of liquid 32 in this range is achieved by cycling heating element 42 on and off in response to signals from heater temperature sensors 48 and liquid temperature sensors 50 in a similar manner to that described during pre - heating of liquid 32 . when the invention is ready to treat a patient , microcontroller 66 also monitors inflate switch 74 to determine when it is activated by the user . when the invention is ready for use to treat a patient , the user inserts the distal end of disposable component 4 through the cervical opening of the patient until flange 20 rests against the cervix preventing further insertion . this operation precisely locates the distal balloon 14 and distal sheath 18 in the uterine cavity as required for treatment . it is expected that the patient has been prepared for surgery and may have received a sedative or anesthetic . it is also expected that the user will have confirmed that the depth and volume of the uterine cavity are suitable for use of the described invention . after the distal balloon 14 and associated components have been properly located in the patient , the user activates inflate switch 74 to begin treatment . when microcontroller 66 detects activation of inflate switch 74 , it proceeds to implement a treatment cycle as follows . first heating element 42 is turned off . next , timer 68 is activated and pneumatic pressurizing means 52 releases the − 100 mmhg vacuum in pneumatic chamber 40 to atmosphere through 2 - way , 2 - position valve 56 . pneumatic pressurizing means 52 is then activated to generate and maintain a pneumatic pressure of 180 mmhg in pneumatic chamber 40 . this has the immediate effect of forcing 165 c liquid 32 from the proximal balloon 26 through catheter 16 and liquid ports 30 into distal balloon 14 which is located in the uterus of the patient . after a short period of time , the liquid in distal balloon 14 reaches a steady state pressure of 180 mmhg . at this pressure , the uterus will be fully distended and distal balloon 14 will be filled with heated liquid 32 and be in contact with substantially all of the walls of the uterine cavity . in this steady state , the liquid pressure inside distal balloon 14 will be essentially equal to the liquid pressure inside proximal balloon 26 and the pneumatic pressure inside pneumatic chamber 40 . the microcontroller operates to automatically maintain this pressure in pneumatic chamber 40 , and thereby distal balloon 14 for a period of 90 seconds as indicated by timer 68 . during this 90 second period thermal energy from heated liquid 32 within distal balloon 14 is dissipated to the surrounding tissue of the uterus and results in the desired cauterization of the endometrial tissue . during this 90 second period , the temperature of liquid 32 in distal balloon 14 will decrease as the heat energy is dissipated to the surrounding tissues . the nature of this cooling will be dependent of the specific anatomy of the uterine cavity undergoing treatment . in some cases in order to minimize this cooling effect it may be advantageous for microcontroller 66 to pulse the pneumatic pressure in pneumatic chamber 40 during the treatment period in order initiate flow back and forth between distal balloon 144 and proximal balloon 26 to continually mix the volume of heated liquid 32 contained within disposable component 4 . when the 90 - second treatment period is completed , microcontroller 66 proceeds to control operation of the invention as follows . first , timer 68 is reset and pneumatic pressurizing means 52 releases the 180 mmhg pressure in pneumatic chamber 40 to atmosphere through 2 - way , 2 position valve 56 . pneumatic pressurizing means 52 is then activated to generate and maintain a pneumatic pressure of approximately − 100 mmhg in pneumatic chamber 40 . this has the immediate effect of withdrawing liquid 32 from distal balloon 14 back into proximal balloon 26 through catheter 16 and liquid ports 30 . after 15 seconds as indicated by timer 68 , microcontroller 66 generates a message to the user via display means 10 indicating that distal balloon 14 has been deflated and can be removed from the uterus of the patient . it is expected that the user will then remove the apparatus from the patient . after another 120 seconds as indicated by timer 68 , microcontroller 66 operates to vent pneumatic chamber 40 to atmosphere through 2 - way , 2 - position valve 56 and generates a message to the user via display means 10 indicating that the user can remove and discard disposable component 4 . microcontroller 66 then monitors disposable component detection means 55 in order to detect when disposable component 4 is removed from reusable component 2 for discard . when removal is detected microcontroller 66 continues to poll for installation of a new disposable component 4 in order to allow another patient to be treated or the invention can be turned off by the user using on / off power switch 72 . the described operation of the invention is for illustration purposes only . it will be obvious to one skilled in art that there are numerous possible modifications to the operation of the invention as described . fig7 a shows deployment of the distal end of disposable component 4 during treatment of a 7 cm deep uterus which is the smallest indicated uterus for use of the preferred embodiment of the invention . fig7 b shows deployment of the distal end of disposable component 4 during treatment of a 12 cm deep uterus which is the largest indicated uterus for use of the preferred embodiment of the invention . the outlines of distal balloon 14 prior to inflation 76 and after inflation 78 with liquid 32 to a pressure of 180 mmhg . this shows how the invention operates to treat the indicated range of uterine sizes after inserting disposable component 4 through the cervical canal until flange 20 prevents further insertion . when the user properly operates the device by inserting disposable component 4 through the cervical opening and into the uterus of a patient in this manner , the invention does not require a user to adjust insertion depth based on uterine length , minimizing the risk of perforating the uterus , and providing thermal protection of the cervical canal by ensuring distal sheath 18 and the underlying thermal insulating material 36 are properly located between the internal os and external os of the cervix . fig8 shows an alternate embodiment of the device . in this alternate embodiment , heating element 42 , and one or more of liquid temperature sensors 50 are located within distal balloon 14 . this embodiment further includes a multi - conductor electrical cable 80 and an electrical connector 82 which operates to make electrical contact when pneumatic fitting 24 is engaged by locking connectors 54 . multi - conductor electrical cable 80 and electrical connector 82 function in order to provide power from electrical power supply 70 to heating element 42 and to control operation of said heating element 42 via operation of microcontroller 66 . multi - conductor electrical cable 80 and electrical connector 82 also function to convey signals from liquid temperature sensors 50 indicative of the liquid temperature within distal balloon 14 to microcontroller 66 . in the alternate embodiment , heating element 42 is a liquid - tight , 40 w , electrical resistance type heater and liquid temperature sensors 50 are t - type thermocouples . operation of the alternate embodiment differs from the preferred embodiment in that liquid 32 is not heated prior to initiation of treatment , but is instead heated after distal balloon 14 is inserted through the cervical opening into the uterus and inflated to a pressure of 180 mmhg by pneumatic pressurization of pneumatic chamber 40 . when the user initiates treatment by pressing inflate switch 74 , microcontroller 66 operates to inflate distal balloon 14 as described in the preferred embodiment then operates control heating element 42 to heat the liquid within the distal balloon to a pre - determined temperature as indicated by liquid temperature sensors 50 . in the alternate embodiment microcontroller 66 maintains said liquid temperature for a predetermined time as measured by timer 68 before withdrawing the liquid into the proximal balloon 26 by operating pneumatic pressurizing means 52 to draw a negative pressure in pneumatic chamber 40 . in this alternate embodiment it is desirable that liquid 32 be of a viscosity such that it readily flows through catheter 16 and liquid ports 30 for inflation of distal balloon 14 . for example , saline solution can be used as liquid 32 , in which case heating of the liquid is restricted to temperatures substantially below 100 c to prevent boiling . in the alternate embodiment and using saline solution as liquid 32 a liquid temperature of approximately 85c and a treatment time of approximately 10 minutes have been found effective to cauterize the endometrium . use of other liquids with low viscosity and higher boiling points , such as perfluoroperhydrophenanthrene ( c14f24 ) allows use of higher treatment temperatures and shorter treatment times . it will be appreciated by one skilled in the art that a variety of alternate embodiments exist for the disclosed inventions which may also specifically include a combination of the two described embodiments such that heating of liquid 32 is initiated by heating elements located in both reusable component 2 and disposable component 4 . specifically this combination would be advantageous where it is desired to locate heating element 42 in distal balloon 14 , however , liquid 32 is highly viscous and must be heated above ambient temperature by a heating element external to distal balloon 14 in order to adequately flow through catheter 16 and liquid ports 30 for inflation of distal balloon 14 . for example , this allows use of 100 % glycerin as the liquid 32 , which is highly viscous at room temperature but can be heated to temperatures of over 165 c without boiling . it will also be recognized that the described apparatus could readily be modified by replacing heating element 42 with a cooling means in order to enable injection of cold liquid into distal balloon 14 to cauterize the endometrium . similarly it will be understood by one skilled in the art that the disclosed apparatus could readily be modified to effect thermal balloon ablation of other cavities or ducts in the human body , such as the urethra for treatment of pathological conditions of the prostate gland . it will be apparent from the foregoing that , while particular forms of the invention have been illustrated and described , various modifications can be made without departing from the spirit or scope of the invention . accordingly , it is not intended that the invention be limited except as by the appended claims .
an apparatus and method for causing necrosis of tissue and specifically intended for thermal ablation of the uterine cavity to cauterizing the endometrial tissue . the apparatus includes a liquid - tight , liquid filled system having a distal flexible member ; a proximal flexible member ; and a catheter joining and providing a liquid path between these distal and proximal members . the apparatus further includes a pressurizable pneumatic chamber into which the proximal flexible member is inserted and a means to controllably heat the contents of the pneumatic chamber . the system operates to : first withdraw substantially all of the liquid into the proximal flexible member contained within the pressurizable pneumatic chamber ; second to heat this liquid to a temperature such that it can cause tissue necrosis ; and third to force the heated liquid from the proximal flexible member into the distal flexible member where it is maintained for a predetermined time and at a predetermined pressure . where this distal member has been inserted into a uterine cavity or is otherwise is in contact with living tissue , the presence of the heated liquid results in tissue necrosis and cauterization .