Abstract:
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.

Description:
TECHNICAL FIELD  
         [0001]    The disclosed invention relates to an apparatus or device for effecting hyperthermia in a body cavity or duct. More specifically, the invention relates to apparatus and methods using a balloon or similar flexible bladder which is inserted into the uterus and filled with a heated liquid at a known pressure and for a known time in order to cauterize (“ablate”) the endometrium of the uterus. This method of treatment is known as “thermal balloon ablation”.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0002]    Medical treatments involving ablation of the endometrium of the uterus are well known in the prior art. The endometrium is the portion of the uterine lining to which an embryo normally attaches and is responsible for the menstrual cycles. Such ablation treatments typically involve either the direct or indirect application of heat or cold to the endometrial tissue. Commonly, ablation devices and techniques have been used to treat menorrhagia (a condition of excessive menstrual bleeding) by cauterizing, or inducing necrosis of the endometrial lining. This cauterization prevents further proliferation of the endometrium and may result in permanent relief of menorrhagia symptoms.  
           [0003]    Apparatuses for thermal balloon ablation are well known in the prior art. For applications to treat the endometrium of the uterus, thermal balloon ablation apparatuses typically comprise a distensible balloon which is inserted into the uterus through the external opening of the cervix. The balloon is then inflated with a liquid to expand the balloon such that it is in contact with substantially all of the uterine cavity. This liquid is then heated to a controlled temperature by a heating element within the balloon and the liquid is maintained at this temperature for a predetermined period of time. After this period of time has elapsed, the liquid is withdrawn and the balloon removed from the uterus. The heat energy which is transferred from the liquid filled balloon to the surrounding tissues of the uterus causes the desired cauterization of the endometrium. There are many examples of such devices in the prior art, for example those disclosed by Stevens et al—U.S. Pat. No. 5,800,493, and Wallsten et al—U.S. Pat. No. 5,693,080 &amp; U.S. Pat. No. 5,571,153.  
           [0004]    Typically the volume of liquid required to inflate the balloon ranges between 5 ml and 30 ml and is dependent on the natural volume of the uterine cavity and the liquid pressure. According to studies published in the medical literature, the liquid pressure should not exceed 180 mmHg applied to the uterine cavity walls above which there is risk of mechanical damage to the deeper tissue of the uterus.  
           [0005]    Variations on thermal balloon apparatuses and methodologies include cryogenic apparatuses which use cooled liquid rather than heated liquid to achieve necrosis of the tissue (such as that disclosed by Lafontaine et al—U.S. Pat. No. 5,868,735) and apparatuses in which heated liquid is circulated through the uterus without the benefit of a flexible balloon to contain the liquid (such as that disclosed by Goldrath—U.S. Pat. No. 5,437,629).  
           [0006]    A variety of alternatives to thermal balloon ablation are known for cauterization of endometrial tissue. These includes the use of microwave, RF, laser, electrical current or similar energy sources to heat a surgical probe inserted through the cervix and which is manipulated by means of direct hysteroscopic visualization. These devices typically require a highly skilled operator and produce treatment results which are more variable than those which can be achieved through thermal balloon ablation techniques. Such alternative ablation techniques also pose higher risk of perforating the uterus, normally require use of general anesthesia, and have a higher incidence of post-operative complications than thermal balloon ablation techniques.  
           [0007]    In spite of the potential advantages of thermal balloon ablation techniques over alternative treatment methodologies, problems with the thermal balloon ablation apparatuses in the prior art have prevented such devices from being adopted widely for use in the treatment of menorrhagia.  
           [0008]    Thermal balloon ablation systems in the prior art typically rely on heating elements located within the balloon. During heating, these devices often develop temperature gradients in the liquid which can result in uneven treatment of the endometrial surface. Typically the observed effect is to over-treat the area of the endometrium directly above the heating element and under-treat the area of the endometrium located directly below. This effect is magnified if the heating element within the balloon is inserted at an angle relative to the anterior/posterior plane of the uterus such that after inflation the heating element is located closer to the anterior wall of the balloon. Placement of the heating element relative to the balloon walls is difficult to control in practice. To reduce this problem, some inventions in the prior art include provision of an impeller, reciprocating piston or similar mechanical means to stir the liquid during heating (such as those disclosed by Neuwirth et al—U.S. Pat. No. 5,460,628 and Saadat et al U.S. Pat. No. 5,827,269) or utilize balloons which allow injection and re-circulation of heated liquid via multiple lumens, typically an “intake” lumen and an “exhaust” lumen (such as that disclosed by Lafontaine et al—U.S. Pat. No. 5,868,735). Furthermore, pulsing the liquid pressure is an alternative means to achieve more uniform mixing of the liquid (as described by Wallsten et al U.S. Pat. No. 5,957,962). However, such circulating methodologies add cost and complexity to the apparatus and the ability to achieve desired temperature uniformity depends among other factors on the volume of liquid within the balloon.  
           [0009]    Thermal balloon ablation devices in the prior art such as that disclosed by Stevens et al—U.S. Pat. No. 5,800,493 have also relied on the operator to provide the liquid for inflation of the balloon and heating. This has limited the variety of liquids to those typically found in a clinical environment (e.g. D5% W or saline). Such liquids are generally water based and therefore cannot be heated above approximately 100C, at which temperature these solutions begin to boil at sea level. Heating liquid to the boiling point can result in a dangerous increase in balloon volume due to expansion of gas and in uneven treatment since the presence of this gas pockets in the balloon act to thermally insulate the adjacent tissue. The maximum temperature limitation of these liquids has resulted in relatively long treatment times; it is well established in the research and in clinical practice that it requires in approximately 8 minutes to cauterize the endometrium by thermal balloon ablation using liquid temperatures of 85C. Furthermore, the use of liquid temperatures in the range of 70-90C makes the use of liquid heating means external to the uterus or balloon ineffective since in this temperature range there is insufficient heat energy contained within the volume of liquid within the uterus to adequately cauterize the endometrium. In devices that employ heating means external to the balloon in the uterus and which use liquid temperatures below 100C (such as that disclosed by Chin U.S. Pat. No. 5,449,380) it is generally necessary to continuously circulate the liquid between the balloon and the external heating means in order to maintain an elevated liquid temperature within the uterus and to achieve the desired treatment. In addition, devices with heating elements located in the balloon within the uterus prohibit the use high viscosity liquids (such as 100% Glycerin) which resist flow at ambient temperatures but once heated become less viscous and can readily flow through a catheter to inflate a balloon placed in the uterus.  
           [0010]    Systems which require the operator to supply the inflation liquid are also complicated for the operator to use. It is necessary for the operator to obtain a source of sterile liquid, inject the liquid into the system, check for leaks, purge gas or excess liquid from the system, and then dispose of the heated liquid after treatment. This process also compromises the sterility of the system since there is potential for non-sterile or contaminated liquid to circulate within the balloon. In the event of a balloon leak or rupture, this non-sterile liquid is released into the uterine cavity and could result in infection.  
           [0011]    Devices in the prior art typically rely on mechanical actuators, syringes, or liquid pumps which come into contact with the treatment liquid in order to control inflation and pressurization of the balloon, these can be expensive, unreliable, and subject to contamination. Often these systems require the operator to manually inject liquid to fill the balloon. Furthermore such systems (such as that disclosed by Stevens et a—U.S. Pat. No. 5,800,493) typically have expensive disposable components as these components often include hoses, valves, connectors, electrical wiring, syringes, and heating elements which must be disposed of after each use. Wallsten et al have attempted to address this problem in the invention disclosed in U.S. Pat. No. 5,957,962 in order to provide an inexpensive disposable component however the described system still requires the addition of liquid from an external source, purging of gas from the system and relies on a mechanical apparatus and actuators to inject and remove liquid from the treatment balloon.  
           [0012]    Often it is difficult for the operator to control inflation pressure and there is not adequate means to control this pressure in response to changes in uterine volume during treatment (typically the uterus relaxes and expands as treatment progresses and therefore it is desirable to increase the volume of liquid in the balloon to maintain a constant inflation pressure). Wallsten et al U.S. Pat. No. 5,693,080 discloses apparatus intended to allow automated control of inflation pressure through mechanical actuation of syringes or similar means however this is costly and does not allow fine control of pressures. Wallsten et al further disclose a means for providing overpressure relief in the event of a increase in balloon pressure such as that which might be caused by a sudden contraction of the uterus during treatment however this does not provide a practical or inexpensive means for automated control of balloon inflation, deflation, and liquid pressure.  
           [0013]    Prior art devices also rely on the operator to sound the depth of the uterus then insert a catheter or treatment element to a depth of no greater than the previously sounded depth. This requires effort on the part of the user to measure depth and observe insertion depth as marked on the treatment device. There is a danger of perforating the uterus by over-inserting the catheter if the clinician does not perform this operation properly.  
           [0014]    In providing thermal balloon ablation treatment, it is desirous to: provide uniform cauterization of the endometrial tissue; ensure that any material which can potentially come into contact with the patient is sterile; provide the treatment in as short a period of time as possible; deliver the treatment in a manner which does not depend on the skill level of the operating clinician; and minimize the cost of any disposable components associated with the treatment apparatus. It is further desirable to avoid cauterization of the cervical canal during treatment, and to minimize the risk of perforation of the uterus when the balloon is inserted through the cervical opening or during the treatment period.  
           [0015]    Ideally the device should be simple for the operator to use and should require minimal preparation for use by the operating clinician.  
           [0016]    Accordingly, the present invention provides an apparatus for causing necrosis of a body cavity or duct, specifically the uterus, said apparatus comprising:  
           [0017]    a disposable portion of the apparatus comprising a sealed system consisting of a liquid within said sealed system, an elongated distal section with a flexible balloon (or bladder) attached to it, a proximal flexible balloon (or bladder), and a means for connection to a permanent non-disposable apparatus;  
           [0018]    a means for heating said liquid; and  
           [0019]    a permanent non-disposable apparatus comprising, a pneumatic pressurizing means for initiating flow of the liquid within said sealed system of the disposable portion of the apparatus, connection means for said disposable portion to permanent portion, and a controlling means for heating, pneumatic pressure, and time.  
           [0020]    An object of the invention is to provide an apparatus which furnishes a means for shortened treatment time by incorporating a sealed disposable component containing a volume of liquid provided by the manufacturer. A liquid filled and sealed disposable apparatus provides one advantage as it allows the use of liquids which are not typically encountered in a clinical environment and which can be heated to temperatures in excess of 100C without boiling (for example 100% Glycerin). This allows improved cauterization of the endometrial lining of the uterus and shortens treatment times from 8 minutes at 85C to approximately 1.5 minutes at 165C. Furthermore, by pre-heating the liquid external to the patient, high viscosity liquids (such as 100% Glycerin) can be used which flow readily at higher treatment temperatures. Because of the high viscosity at ambient temperatures, such liquids could not be readily utilized in apparatus where the heating means is located inside the balloon which is inserted into the uterus.  
           [0021]    Another object of the invention is to provide a means of ensuring uniform treatment of the uterine cavity. The apparatus achieves the objective by injecting a pre-heated, isothermal volume of liquid into the distal flexible bladder within uterine cavity. Therefore at the time of injection into the uterus, all areas of the uterus are contacted with a uniform high temperature (approximately 165 degrees Celsius) liquid.  
           [0022]    Another objective of the apparatus is to provide a low cost, easy to use system, that is safe and effective. The described apparatus provides for improved ease of use and reduced costs by using a disposable component comprising primarily: two flexible enclosures joined by a liquid path and containing a liquid; and a fitting which permits the proximal flexible enclosure to be sealed inside the re-usable pneumatic chamber. By using a sealed system containing a bolus of liquid, the operator simply installs the disposable cartridge and initiates heating. There is no need to source liquid, fill the system, or purge gas from the system. This makes the apparatus much easier to use and improves patient safety by ensuring sterility of the system. Since the liquid is contained in a sealed system and is driven by pneumatic means, in the event of a balloon rupture only sterile liquid can be released into the uterus. The disposable component does not include valves or fluid pumping means and can therefore be manufactured for minimal cost.  
           [0023]    A further object of the invention is to automate balloon inflation and control of balloon inflation pressure. The described apparatus provides improved control of balloon inflation pressure by modulating pneumatic pressure within a chamber external to the patient. This pressure can be readily monitored and automatically controlled with a high degree of accuracy to achieve the desired inflation pressure of the distal balloon during the treatment period, adapting quickly to changes in uterine volume due to relaxation or contraction of the associated musculature. By using pneumatic pressure to transfer liquid from the proximal flexible balloon into the distal flexible balloon and withdraw liquid from the distal flexible balloon, the system achieves a high degree of control and reduces user errors.  
           [0024]    Yet another object of the invention is to provide a physical means to indicate when the proper depth of insertion of the balloon is achieved. The described apparatus uses a soft rubber flange (“cervical tab”) around the insertion catheter which is larger than the cervical opening. This prevents insertion of the catheter beyond a predetermined depth into the uterus. The apparatus is configured such that when the catheter is inserted until this cervical tab rests against the proximal cervical opening, the associated treatment balloon can deploy to treat the indicated range of uterine sizes and volumes. Before treatment, the operator confirms by examination that the uterine depth and volume fall within this predetermined range, then the operator simply inserts the balloon until the cervical tab rests against the cervix. The operator does not need to change the depth of insertion or manner of use for different patients. As a result, there is minimal risk of perforating the uterus and treatment methodology is greatly simplified for the user.  
           [0025]    A further object of the invention is to provide a means of preventing any treatment to the cervical canal. This is achieved by a thermal insulating sheath, which surrounds the liquid delivery catheter. When the treatment balloon and liquid delivery catheter are inserted such that the cervical tab rests against the cervix, the insulating sheath located distal to the cervical tab is precisely positioned within the cervical canal. This sheath has thermal insulating capabilities, which limit the heat transfer between the liquid delivery catheter and the patient&#39;s cervix and prevents unwanted treatment of this area.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 a  and FIG. 1 b  provide an overview of the embodiment of the invention. FIG. 1 a  shows the reusable and disposable components separately, FIG. 1 b  shows the invention with the disposable component installed in the reusable component.  
         [0027]    [0027]FIG. 2 provides a detailed cross sectional view of the disposable component.  
         [0028]    [0028]FIG. 3 shows a detailed cross sectional view of the pneumatic chamber and associated components of the distal end of the reusable component.  
         [0029]    [0029]FIG. 4 shows a detailed cross section of the proximal end of the disposable component and the reusable component when the reusable component is installed such that it is ready for use.  
         [0030]    [0030]FIG. 5 provides details of the preferred embodiment of the pneumatic pressurizing means.  
         [0031]    [0031]FIG. 6 shows details of the control system contained within the reusable component.  
         [0032]    [0032]FIG. 7 a  shows deployment of the distal end of disposable component during treatment of a 7 cm deep uterus which is the smallest indicated uterus for use of the preferred embodiment of the invention.  
         [0033]    [0033]FIG. 7 b  shows deployment of the distal end of disposable component during treatment of a 12 cm deep uterus which is the largest indicated uterus for use of the preferred embodiment of the invention.  
         [0034]    [0034]FIG. 8 shows an alternate embodiment of the device in which a heating element is contained within the distal balloon.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0035]    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.  
         [0036]    In accordance with the present invention as shown in FIG. 1 a  and FIG. 1 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 .  
         [0037]    [0037]FIG. 2 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 165C. 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.  
         [0038]    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 10C without boiling. In the preferred embodiment 100% Glycerin is used which can be heated to temperatures above 165C 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.  
         [0039]    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 49C 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.  
         [0040]    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.  
         [0041]    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.  
         [0042]    [0042]FIG. 3 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 .  
         [0043]    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.  
         [0044]    [0044]FIG. 4 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.  
         [0045]    [0045]FIG. 5 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 FIG. 5 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 .  
         [0046]    [0046]FIG. 6 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.  
         [0047]    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 .  
         [0048]    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 .  
         [0049]    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 200C as indicated by heater temperature sensors  48 , microcontroller turns heating element  42  off until the measured heater temperature drops below 165C. 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 165C. 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.  
         [0050]    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 160C and 170C. 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.  
         [0051]    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.  
         [0052]    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 165C 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 .  
         [0053]    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.  
         [0054]    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 .  
         [0055]    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.  
         [0056]    [0056]FIG. 7 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. FIG. 7 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.  
         [0057]    [0057]FIG. 8 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, 40W, electrical resistance type heater and liquid temperature sensors  50  are T-type thermocouples.  
         [0058]    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 100C 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.  
         [0059]    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 165C without boiling.  
         [0060]    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.  
         [0061]    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.