WO1999008633A1

WO1999008633A1 - Device for heat treatment

Info

Publication number: WO1999008633A1
Application number: PCT/SE1998/001456
Authority: WO
Inventors: Hans I. WALLSTÉN
Original assignee: Wallsten Hans Ivar
Priority date: 1997-08-19
Filing date: 1998-08-11
Publication date: 1999-02-25
Also published as: AU8654798A; SE9702983D0

Abstract

A device for carrying out thermal treatment in a body cavity or duct, in particular the prostate, comprising an elongate and hollow application catheter (6), heat-releasing element (19, 79), which is surrounded by an elongate housing (20, 77), a flexible and/or elastic balloon (2, 63) surrounding said housing in a liquid-tight manner. Further including an inlet passage (27, 95), an outlet (22, 54, 93) from the housing (20, 77) being arranged for the supply of a first heat-transmitting medium under pressure for expansion of the flexible balloon (2, 63) to exert, pressure on surrounding walls of said cavity or duct. Further comprising a viewing opening (5) proximal to the balloon (2, 63) for visual access to the exterior of said catheter (6) by accommodating an endoscope therein, characterized by means (30) allowing a second medium for irrigation of the endoscope lens and for cooling of the circumferential area, thereby protecting tissue surrounding said circumferential area from excessive heating.

Description

DEVICE FOR HEAT TREATMENT

Field of the invention

The present invention relates to devices for thermal treatment of living animal tissue, in particular the prostate .

Background of the invention

Although the present invention is restricted only to devices for carrying out thermal treatment in a body cavity or duct the invention will be particularly described in relation to treatment of the prostate.

Benign Prostatic Hyperplasia (BPH) is a disease causing obstruction of the urinary flow because of adenoma- tous tissue. The most common treatment is surgery, such as prostatectomy or transurethral resection (TURP) . There are also alternative methods developed with the aim to make the treatment less invasive. One transurethral method is based on mechanical dilation of the prostate with the help of a balloon catheter dilated to a predetermined diameter at high pressure. The positioning of the balloon is important and there are different means suggested, such as the use of a cystoscopic system (ASI Uroplasty Prostatic Catheter System) for the precise placement of a balloon for dilation between the apex and the neck of the bladder. Other methods are surgical and based on the use of immediate ablation by heat, such as laser, resectoscope or radio frequency waves, e.g. between two needles, all under visual control. According to other methods based on heat the temperature is raised in a part of the tissue to a level sufficient to create necrosis by the use of a transurethral catheter during a reasonable treatment time, whereafter the necrotic tissue is sloughed off and partially resorbed. An energy source used for this type of treatment is radiofrequency microwave. Another method having for its purpose to provide a similar effect is based on the combination of balloon dilation and thermal conduction of heat from a dilated balloon in a catheter using hot water circulated through the catheter from an externally positioned heat exchanger (cf. US patent 5,257,977). At a balloon temperature of 60°C it is possible to achieve a temperature of 55°C at a depth of 4 mm, which probably requires a treatment time of at least one hour. In all thermo-therapeutic methods based on necrosis for the treatment of BPH the aim is to elevate the temperatures sufficiently to cause effective necrosis of the target tissue during a reasonable treatment time during one single session but so that the temperatures outside the target zone are kept so low that there is no risk of thermal damage. It is therefore particularly important that the temperature in such areas as the sphincter, urethra, rectal wall and the bladder are kept below 41- 43°C during the course of treatment. There are different suggestions to protect such areas from overheating. For instance, the European patent application 0 370 890 discloses a microwave catheter device using radioreflecting screens and cooling means to protect such areas. This device and similar devices are very complicated and need urethral and rectal probes to monitor the different temperatures.

A disadvantage with the device according to US 5,257,977 is that it is difficult to position the balloon, and that temperature of the balloon must be re- stricted to about 60°C because of the risk for thermal damage of the sphincter and the urethra. As a consequence of the relatively low heating temperature the treatment time has to be kept long to achieve sufficiently deep necrosis . A particular problem is that the transurethral catheter must contain several passageways for the hot fluid, guidewires, drainage of urine (due to long treat- ment time) which have to be surrounded by thermal insulation. Due to the restrictions in catheter diameter there is a limit in the insulation thickness and thus in the maximal temperature of the circulated liquid. Another di- sadvantage is that a number of balloon catheters of various lengths must be available, to match the different lengths of the patient's prostate.

Summary of the invention The present invention has for its purpose to provide new techniques for carrying out thermal treatments in body cavities or ducts, particularly in the urinary tract and especially in the prostate and bladder neck eliminating or reducing drawbacks of the prior art. The main object of the present invention is to provide a device enabling thermal treatment of the target region at a high temperature and high pressure to create necrosis of the target tissue sufficiently deep during a short treatment time. Another object of the invention is to provide such a device by which in spite of a high treatment temperature in the target region areas adjacent to said region can be maintained at acceptable temperature levels, such as below 40-43°C to protect such areas from heat damage. Yet another object of the invention is to provide a device which can be precisely positioned under visual control for thermal treatment under pressure of target regions of a living animal body.

Still another object of the invention is to provide a device which enables thermal treatment under pressure of the region between the apex and the bladder neck so that there will be no risk for thermal damage of the adjacent organs, such as the rectal wall, the bladder, the external sphincter and the proximal part of the urethra. A further object of the invention is to provide a device which enables thermal treatment of body cavities or ducts under efficient heat transfer under pressure to provide an even and complete treatment of the target region in its entirety.

Still another object of the invention is to provide a device in which the active length of the balloon can be adjusted to adapt to body cavities or ducts of varying dimensions .

A further object of the invention is to provide a device which in a deflated state can be designed with a small catheter diameter to avoid unnecessary dilation of the body duct in connection with the introduction of a catheter.

Another object of the invention is to provide a device whereby the active length of the balloon can be selected or adjusted as desired. Yet another object of the invention is to provide a device whereby a distinct separation between a hot treatment zone and a cold zone outside of the target site can be provided.

For these and other objects which will be clear from the following disclosure the invention provides for a device for carrying out thermal treatment in a body cavity or duct, the excess path of which is narrow. Accordingly, although the invention is not restricted to such application it is particularly suited for a treatment of the prostate. The device comprises an elongate and hollow application catheter or shaft intended to be inserted into said cavity or duct and comprising a centrally located, heat-releasing element which is surrounded by an elongate housing, a flexible and/or elastic enclosure surrounding said housing in a liquid-tight manner, further including means for supplying energy to the heat-releasing elements, an axially operating inlet passage being arranged at the proximal part of the housing, further comprising an outlet from the housing arranged for the supply of a first heat-transmitting medium under pressure for the expansion of the flexible enclosure to accomodate to and to exert a controlled pressure on surrounding walls of the cavity or duct. The device further comprises a viewing opening located in said shaft proximal to the enclosure for visual access to the exterior of said shaft by acco- modating an endoscope therein. The device is characteri- zed by means allowing, within said catheter, distal entrance passed said opening and proximal exit of a second medium for cooling of the circumferential area between said opening and the proximal end of the balloon, and for irrigation of the endoscope lens, thereby protecting tissue surrounding said circumferential area from excessive heating.

In the instant disclosure the terms "distal" and "proximal" refer to the forward end and the rear end of the part of the device to be inserted into a body cavity or duct. Thus, the distal end of the instrument is the front end of the instrument initially entering such body cavity or duct.

It is preferred to provide the device according to the invention with means for internal mixing of said first medium within the balloon or with means for internal circulation of said first medium through the housing to flow in an opposite direction outside the container within the balloon.

In one embodiment of the device according to the in- vention means is provided to generate a reciprocating motion to a quantity of said first medium, which motion is transferred via the inlet passage to the interior of the housing and of the balloon to agitate or circulate said first medium therein. In such embodiment the internal circulation suitably has a capacity at steady state conditions of replacing the void volume inside the balloon of at least about 2 times per minute with regard to said first medium.

In a preferred embodiment of the device according to the invention there is provided at least one first back valve arranged in association with an inlet for said first medium arranged in the housing on the other side of the element relative to the outlet, and such device comprises a partition placed between the inlet and the element or between the element and the outlet, respectively, to form a chamber and which is provided with an axial aperture containing a second back valve which is oppositely acting relative to said first back valve placed in the inlet, said means for the flow of said first medium in an internal circuit being arranged to provide a reciprocating movement of a small quantity of said first me- dium enclosed in the inlet canal of the device after expansion of the enclosure, whereby the inlet is closed and the outlet is open, or the inlet is open and the outlet is closed, respectively, thereby providing circulation of the medium in a closed circuit. As an alternative embodiment the device may include an elongate housing provided with several openings allowing access for said first medium via an inlet passage to the interior of the balloon, whereby said means for internal mixing provides agitation of said first means inside the balloon.

A preferred embodiment of said means for the flow of said first medium in an internal circuit is constituted by a reciprocating piston or oscillating membrane.

According to a preferred embodiment of the device according to the invention the distal end of the balloon may be sealed around the distal end of the housing and be surrounded by an axially displacable sleeve. By axial displacement of such sleeve the active length of the enclosure or balloon can be adjusted and adapted to the organ to be treated. The sleeve can suitably be designed as a cap having a rounded distal end. Such axially displaceable sleeve can be replaced by a set of sleeves sof varying length, whereby the active length of the balloon can be selected. Alternatively, a tube of overlength can be cut to the desired length. As yet another alternative a tape or similar means can be applied around the distal end of the balloon. To enable drainage of gas from the interior of the balloon a drainage valve can be arranged within such cap and can be operable from the outside for such drainage of gas . To obtain a balloon or enclosure which is easy to handle and will not be subject to the formation of wrinkles the enclosure or balloon can have a multi-layered design, wherein the balloon comprises an inner elastic and liquid-tight layer, and an outer layer of limited elasti- city. In this manner the balloon when deflated will return to an unwrinkled state of small diameter.

A preferred arrangement in this multi-layered design, wherein the term "multi" means two or more layers, is constituted by a triple-layered arrangement comprising said inner elastic layer, an intermediate layer of limited elasticity corresponding to said outer layer, and an outer elastic layer.

In a particularly preferred embodiment of the device, said layer of limited elasticity is comprised of a braided or woven tube, the filaments of which have limited elasticity, at least in a circumferential direction.

According to an alternative preferred embodiment said layer of limited elasticity is comprised of a winding of a filament or thread of limited elasticity. In a particularly preferred embodiment of the device according to the invention a chamber is arranged in a passage allowing introduction of said first medium to reach the interior of the housing. A body is placed in this chamber and is movable between distal and proximal ends of the chamber while allowing a restricted flow of said first medium around and/or through the body for filling and emptying the balloon.

It is preferred that this restricted flow takes place via a circumferential play between said body and the surrounding body wall.

In another embodiment of the device according to the invention the application catheter comprises means al- lowing, within said catheter, entrance of a second medium to pass said opening for irrigation of the endoscope lens, and means acting to provide a reciprocating motion to a quantity of said first medium, said motion being transferred via the inlet passage to the interior of said housing and of said balloon to agitate or circulate said first medium therein. The device further contains a chamber positioned in said passage at the proximal end of said housing, and a body placed in said chamber and mo- vable between the distal and proximal ends of said chamber while allowing a restricted flow of heat-transmitting medium around and/or through said body for filling and emptying the balloon. The body is moving back and forth within the chamber due to the reciprocating motion of a quantity of said first medium.

Brief description of the drawings

In the drawings:

Figure 1 illustrates a diagrammatic side view of an applicator embodying the present invention;

Figure 2 illustrates the state of the art according to US patent 5,571,153, of which the present invention constitutes important developments and improvements;

Figure 3 is a diagrammatic side view illustration through the distal section of an embodiment of the device according to the invention;

Figure 4 illustrates sections along lines II-II and I-I of figure 3;

Figure 5 illustrates a side view of another e bodi- ment of the distal section of the device according to the invention;

Figure 6 illustrates yet another embodiment in a diagrammatic side view of such section;

Figure 7 illustrates a section through a triple- layered balloon or enclosure in deflated and inflated state; and

Figure 8 illustrates a section through an alternati- ve embodiment of the device, said section corresponding to the section along line I-I of figure 4.

Detailed description of the invention Figure 1 illustrates the arrangement of an applicator generally designated 1 comprising a handle 8 and an applicator shaft 6 with a bladder or balloon 2 containing an electric heater 9. The bladder 2 is inflated by a heat-transmitting fluid for the dilation and application of heat to the prostate 3. An endoscope 4 is inserted into the applicator 1, and an opening 5 is arranged in the applicator shaft 6 proximal to the bladder 2. Through this opening 5 the practitioner can control that the external sphincter 7 is positioned on the part of the ap- plicator shaft 6 between the opening 5 and the proximal neck of the heated balloon 2. This part as well as the rest of the shaft 6 in contact with the urethra is cooled in accordance with the invention as explained below.

The applicator handle 8 also serves as a housing for the connections between the shaft or catheter 6 and a control unit (not shown) including en electric source for heat and suitable means for controlling and regulating the treatment temperature, pressure, treatment time, the temperature in the cool parts of the shaft 6 etc. Connec- tion cables for heating and wires for temperature control are indicated at 10, and suitable means 11 are arranged for the supply of heat-transmitting fluid in the form of a liquid via handle 8 to the shaft 6 for filling the applicator and for inflating and deflating the bladder 2. Said means 11 includes a conventional syringe 12, a two- way valve and a stopcock 13 and a tube 14 for connection to the central unit. A connection 18 from a lightsource to the endoscope is included. A tube 15 is arranged for the supply of a liquid in a container or bag 16 via hand- le 8 to the shaft 6 for the cooling of the proximal part of the applicator and for irrigation of the distal lenses of the endoscope according to the invention, which will be explained in detail below. An outlet tube 17 for the cooling/irrigation liquid is provided.

The device according to figure 2 includes a heat applicator 61 in the form of a catheter of a disposable ty- pe, the distal part 63 of which is intended to be inserted into the body cavity, for example the urethra, that shall be heat treated. The applicator has an intermediate part 65 for facilitating insertion of the distal part 63 and for fixation of the position of part 63 in the cavi- ty. The proximal part 67 of the applicator has connecting means 69 for the supply of a compressed medium, for example a liquid from an apparatus 71, for the generation and measurement of pressure via an inlet canal 95 associated with the applicator. Furthermore, the applicator has a connecting means 73 to an electric energy source, not shown, so that an electric current via a cable device 75 can be supplied to a central body 77 containing inter alia a heat-emitting element 79, which may be any type of element such as of self-regulating type, for example of PTC-type, and canals or passages 81 arranged therein or thereabout. Furthermore, the applicator has connecting means 83 to an apparatus 85 for the generation of oscillating pressure impacts to the inlet canal 95 of the applicator after it has been filled with pressurized liquid from apparatus 71. The central body 77 is surrounded by a thin flexible and elastic enclosure or balloon 97 which is brought to expand when the pressure medium is supplied to the interior of the enclosure through canal 95.

The central body 77 with the heat-emitting element 79 has an elongate shape and has a housing 89 surrounding element 79, the housing being provided with apertures 91 in its proximal part and apertures 93 in its distal part.

Figure 3 shows in detail the distal part of the applicator 1 according to one embodiment of the invention. The balloon 2 is flexible and sealed at least at its proximal end 19 to the distal end of the applicator shaft 6 which forms a housing in the form of a container 20 in which a heating means 19 is arranged illustrated as a resistor wire. Outlet/inlet ports 22 are arranged for the inflation and deflation of the balloon 2. Preferably the inflated balloon will form a circular cross-section with a predetermined diameter of about 12-25 mm as inflated at preferable pressures between about 0.5 to 2 atmospheres overpressure. The diameter of the applicator shaft 6 should be as small as possible and not exceed about 6-7 mm to facilitate insertion. The endoscope 4, which can be slid into the applicator shaft 6, is positioned with its distal lens 23 close to the opening 5, so that the practitioner can position the external sphincter juxtaposed the applicator part 24 between the proximal end 21 of the balloon and the ope- ning 5.

A tube 25 is connected to the valve 13 (figure 1) for inflating and deflating the balloon with the liquid which also serves as heat-transmitting fluid for heat rfeleased from the heater 19. The distal end of the tube 25 is attached to a partition 38, which contains the inlet/outlet hole 27 for the liquid in the tube 25 and also serves as a separating and insulating wall in the applicator shaft 6. As described in connection to figure 1, a liquid is introduced in the shaft 6 for the cooling of the proximal part of the applicator. The shaft 6 is separated longitudinally by a horizontal wall 30 creating an upper space 31 and a lower space 32. The cooling liquid is introduced from the handle 8 (figure 1) to the lower space 32 and is flowing in the direction of the arrow 33. The wall 30 ends at 34 allowing the liquid to mount and return as shown by arrows 35 and 36. During treatment the opening 5 is covered by the bulbar urethra, and the liquid will therefore flow back in the upper space 31 to be evacuated via the handle 8 and th eoutlet tube 17 (figure 1) .

The cooling keeps the inner walls of the proximal parts of the applicator shaft 6 cool and particularly the part 24 close to the hot balloon 2 and the separating wall 38. Figure 4 shows the circular cross-section I-I and circular cross-section II-II, respectively, of figures 3 and 5 and particularly how the wall 30 creates an upper space 31 and a lower space 32. 37 depicts cables and wires for the heater 19 and for temperature control (not shown) .

Figure 8 shows an alternative arrangement to that shown by section I-I of figure 4. In this case the flow passages and accommodation of the endoscope 23 is provided by an extruded solid body 39, wherein the different flow passages and accommodation spaces are indicated by reference numerals corresponding to those of figure 4. According to the concept of the invention there is thus created a hot zone at the distal part of the applicator including the inflated part of the balloon 2 and a cool zone of the applicator shaft 6 proximal to the inflated balloon 2. Assisted by the endoscope the pracitio- iner can during treatment keep the applicator in such a position that the external sphincter surrounds the cooled applicator part 24 and is protected from thermal damage, while the thermal treatment at a high temperature is performed between the apex and the bladder neck.

According to this embodiment of the invention the cooling liquid will also on its return serve as an irrigating liquid for the encoscopic lens 23.

In figure 3 there are shown a number of outlets 22 in the tube 20 to allow hot liquid from the heater 19 to circulate, thus transferring heat from the heater 19 to the balloon 2 and into the target tissue by heat conduction.

A more efficient heat transfer can be obtained with the device according to figure 3 if the tube 25 is connected to an oscillating volumetric pump, such as a pis- ton, in the control unit.

Such a pump system is used for the circulation of a fluid inside an elastic enclosure containing heat relea- sing elements surrounded by a housing for hyperthermia treatment in a body cavity and is in a detail described in e.g. US patent 5,571,153, col 9-col 11. (The entire disclosure of this patent is incorporated herein by refe- rence . ) According to this patent circulation is obtained by using oppositely acting back valves arranged in the housing. At every positive pressure stroke from the pump a certain volume of liquid is brought to move forward through a canal in the catheter body into the housing and further out through an open back valve into the space inside the expanded balloon which will be somewhat extended. At every withdrawal of the pump piston a corresponding quantity of liquid will be sucked back when the open back valve closes and another back valve opens. Thus a powerful circulation is provided for under the influence of the oscillating pressure shocks and the valve system. At each positive stroke by the piston a certain quantity of liquid will be forced out through the ports 22 creating turbulence in the liquid enclosed in the balloon 2. At each negative stroke a corresponding quantity of liquid is sucked back through the ports 22 but due to the turbulence a mixture of liquid will be sucked back, which means that an improved heat transfer has been obtained by connecting the device to an oscillating pump. As mentioned earlier it is preferred that the inflated balloon has a circular cross-section with a predetermined diameter. This can be obtained by using preformed flexible thin tubes with low elastiticy. The drawback is that such deflated balloon has wrinkles, which can cause problems at insertion. An alternative solution is to use a multilayer balloon consisting of layers of an elastomer, such as silicon, and an intermediate elastic material which can be extended to a certain upper limit. A suitable material is an elastic clothing used for socks and stockings which is made by a so called stretchable yarn composed by an elastic filament, such as Lycra™, in the core and a less elastic filament such as Nylon™ wound around the core. Such a yarn is highly elastic but there is an upper limit for the extension when the nylon filament is strechted. A clothing woven in the form of a sleeve tube has a certain diameter in released form and can be expanded to a maximal predetermined diameter and resist high pressures.

Figure 7 illustrates cross-sections of such a multilayer balloon in a deflated and inflated state, respectively. The layer of limited elasticity can be comprised of a braided or woven tube, the filaments of which have a limited elasticity at least in a circumferential direction. As an alternative said layer of limited elasticity may be comprised of a winding of a filament of li- mited elasticity placed around the inner elastic layer and wound around said layer expanded to the desired dimension.

The alternative of using a winding of a filament or thread of limited elasticity wound around the innermost elastic layer said elastic layer being placed on a core corresponding to the desired dimension of the layer of limited elasticity, results in several advantages, among which the following can be mentioned.

Using one and the same filament or thread of a limi- ted elasticity the layer of limited elasticity can be made to any dimension, by varying the tension in winding, the degree of close winding etc. Furthermore, the tube of limited elasticity can be made with a cross-section varying along its length, such as conical configuration. This can be done by placing the inner elastic layer onto a core of corresponding configuration.

If balloons of large maximal inflated diameter in devices according to the invention are correctly positioned, as earlier described, and then inflated to a high pressure and the balloon extends beyond the bladder, there can be a tendency for the balloon to migrate into the bladder. Within the scope of the invention, the device can be provided with means for changing length of the balloon prior to insertion for a better match. It is preferred that a multilayer balloon of the type described above is used. One alternative of such means is shown in figure 3. The distal end 43 of the balloon 2 is liquid-tight sealed to the tube or container 20. A part of the distal section 44 cannot expand at inflation as it is surrounded by an axially displaceable end piece in the form of a cap 45. The dotted lines show the outermost end position of the cap 45 and the distal end of the balloon. A locking device consists of a tube 46, attached to the cap 45 with gauges which fit to gauges in a tube 47 with a flange 48. Between the end of the tube 46 and the flange 48 an 0- ring 49 is positioned. Before insertion of the catheter a suitable balloon length is estimated by the practitioner and the cap 45 slid in the correct position. The cap 45 is then locked in position by turning the tube 47 so that the 0-ring 49 is expanded. In figure 3 is also shown a valve for emptying trapped air when filling the device with liquid. The valve consists of a valve seal 50, a valve element 51 and a spiral spring 52. Trapped air is released by pressing a pin through the opening 53 in the cap 45 and compressing the spiral 52.

Figure 5 shows a modified device with improved heat transfer compared to the device shown in figure 3. The device in figure 5 is intended to be connected to an oscillating volumetric pump in a control unit as descri- bed in US patent 5,571,153. An effective circulation of the heat transfer liquid through the heater 21 and the ports 53, 54 and 55 is provided by the flap 56 and a ball 57 acting as oppositely back-acting.

As mentioned earlier, it is within the scope of the invention to create a hot zone around the inflated part of the balloon 2 and a cool zone around the applicator shaft 6 proximal to the balloon to allow effective heat treatment of the prostate but at the same time protect the external sphincter from heat damage. The circulation by using an oscillating pump as described above means however that a certain amount of hot liquid is pulled in the tube 25 (figure 3) at every withdrawal stroke of the pump and a certain amount of cool liquid is moved forward into the container 20.

Due to oscillation turbulence is also created which will result in a mixture of hot and cold liquid in the tube 25 and in the container 20, which reduces the possibilities to keep a sharp limit between the hot and cold zone. An increased flow of cooling liquid could possibly prevent the inner walls of the proximal ports of the applicator shaft to be heated. This is a disadvantage as it means provision of a controlled amount of cooling liquid and also heat losses, which must be compensated by increased generation of heat by the heater.

Figure 6 shows a preferred embodiment according to the invention in which the drawback mentioned above can be eliminated. Distal in relation to the wall 38 in the container 20 a space 60 is arranged in which an axially movable body 61 can freely move longitudinally back and forth. The applicator is connected to an oscillating pump (not shown) for an effective circulation as described in connection with figure 5. Because of the oscillating movement of the liquid in the tube 25 the body 61 will also oscillate .

At the end of each withdrawal stroke of the pump, the body 61 will stop close to the wall 62 which corres- ponds to the wall 38 in figure 5. At the end of every positive pressure stroke of the pump the body 61 will stop in a position corresponding to the dotted lines 63 close to a stop 64. The volume of the space 60 excluding the volume of the body 61 should be about the same or so- mewhat larger than the volume of one stroke of the oscillating pump.

Experience has shown that for an effective heat transfer from the heater 21 through the balloon 2 to the surrounding tissue a certain quantity of the heat transmitting liquid is preferable circulated. The quantity is depending on the stroke volume and the frequency. As ex- ample there can be mentioned that for an effective heat transfer and a balloon volume of about 5 ml a circulated quantity of about 0.2-2.0 ml/second is suitable. It is not a problem to design a pump, such as with a piston, to create an oscillation volume corresponding to these figu- res.

There is, however, limits for achieving an effective circulation inside the balloon 2 at higher frequencies than about 15-25 strokes/second, e.g. because of the back valves in the system which loose its efficiency at higher frequencies. It is therefore preferred to select a relatively high stroke volume, such as about 0.025-0.1 ml, at relatively low frequency, such as 5-25 strokes/second. As mentioned earlier the maximum outer diameter of the applicator should not exceed 6-7 mm to allow easy inser- tion. It means that there is a restriction in diameter if a round body is chosen. Say that a diameter of 4 mm is feasible. This gives for a stroke volume of 60 mm³ a displacement of 5 mm. This can not be achieved by a membrane of a diameter of 4 mm. It must be possible to in- flate, deflate and change the pressure in the ballon during treatment. This problem can not be solved by the use of a diaphragm but is solved in accordance with the present invention by arranging for passage of liquid through and/or around the body 61. Experience has for example shown that if the diameter of a circular piston is 4 mm, it is sufficient with a diameter of the surrounding walls of 4.2 mm to allow sufficient liquid to pass, to inflate or deflate the balloon 2.

Many variations of the invention as described are conceivable and this invention is to be limited solely by the scope of the following claims.

Claims

1. A device for carrying out thermal treatment in a body cavity or duct, the access path of which is narrow, in particular the prostate, comprising an elongate and hollow application catheter (6) intended to be inserted into said cavity or duct comprising a centrally located, heat-releasing element (19,79), which is surrounded by an elongate housing (20,77), a flexible and/or elastic bal- loon (2,63) surrounding said housing in a liquid-tight manner, further including means (10,75) for supplying energy to the heat-releasing element (19,39) and an axially operating inlet passage (27,95) at the proximal part of the housing (20,77), an outlet (22,54,93) from the housing (20,77) being arranged for the supply of a first heat-transmitting medium under pressure for expansion of the flexible balloon (2,63) to exert, under heating, pressure on surrounding walls of said cavity or duct, further comprising a viewing opening (5) located in said catheter (6) proximal to the balloon (2,63) for visual access to the exterior of said catheter (6) by accomoda- ting an endoscope therein, characterized by means (30) allowing, within said catheter, distal entrance to pass said opening (5) and proximal exit of a second medium for irrigation of the endoscope lens and for cooling of the circumferential area between said opening (5) and the proximal end (21) of the balloon, thereby protecting tissue surrounding said circumferential area from excessive heating.

2. A device according to claim 1, characterized by means (85) for internal mixing of said first medium within said balloon (2,63).

3. A device according to claim 1, characterized by means (85) for internal circulation of said first medium through said container (20) to flow in an opposite direction outside said container (20) within said balloon ( 2 , 63 ) .

4. A device according to claim 2 or 3, characterized by means (85) acting to provide a reciprocating motion to a quantity of said first medium, said motion being trans- ferred via the inlet passage (95) to the interior of said container (20,77) and of said balloon (2,63) to agitate or circulate said first medium therein.

5. A device according to claims 3 or 4, characterised by at least one first back valve (56) arranged in as- sociation with an inlet (55) for said first medium arranged in housing (29) on the other side of element (21) relative to said outlet (54), and by a partition (43) placed between said inlet (55) and element (21) or between said element (21) and outlet (54), respectively, for- ming a chamber and being provided with an axial aperture (53) containing a second back valve (57) which is oppositely acting relative to said first back valve (56) placed in inlet (55), said means (75) for the flow of said first medium in an internal circuit being arranged to provide a reciprocating movement of a small quantity of said first medium enclosed in the inlet canal of the device after expansion of the balloon, whereby the inlet is closed and the outlet is open, or the inlet is open and the outlet is closed, respectively, thereby providing circulation of the medium in a closed circuit.

6. A device according to claim 2 or 4, characterized by an elongate container (20) provided with several openings (22) allowing access for said first medium via inlet passage (31,95) to the interior of the balloon (2), whereby said means (85) provides agitation of said first means inside the balloon (2).

7. A device according to any one of claims 2 to 6, wherein said means (85) comprises a reciprocating piston or oscillating membrane.

8. A device according to any one of the preceding claims, characterized in that the distal end of the balloon (2) is sealed around the distal end of the container (20) and is surrounded by a sleeve (45), whereby the active length of the balloon can be selected.

9. A device according to claim 8, wherein said sleeve is axially displacable, whereby the active length of the balloon (2) can be adjusted.

10. A device according to claim 8 or 9, wherein said sleeve is designed as a cap (45) having a rounded distal end.

11. A device according to any preceding claim, cha- racterized by a drainage valve (50-52) positioned at the distal end of said housing and operable from the outside for the drainage of gas from the interior of said balloon (2) .

12. A device according to any preceding claim cha- racterized by a multi-layered balloon comprising, as a minimum, an inner elastic and liquid-tight layer, and an outer layer of limited elasticity.

13. A device according to claim 12, characterized by a triple-layered balloon comprising said inner elastic layer (40), an intermediate layer (41) of limited elasticity corresponding to said outer layer, and an outer elastic layer (42) .

14. A device according to claim 12 or 13, wherein said layer of limited elasticity is comprised of a brai- ded or woven tube, the filaments of which have limited elasticity, at least in a circumferential direction.

15. A device according to claim 13, wherein said layer of limited elasticity is comprised of a winding of a filament of limited elasticity.

16. A device according to any one of claims 4 to 15, characterized by a chamber (60) positioned in said passage (27,95) at the proximal end of said housing, and by a body (61) placed in said chamber (60) and movable between the distal and proximal ends of said chamber (60) while allowing a restricted flow of heat-transmitting medium around and/or through said body (60) for filling and emptying the balloon (2), said body (61) moving back and forth within said chamber (60) due to said reciprocating motion.

17. A device according to claim 16, wherein said restricted flow takes place via a circumferential play bet- ween said body (61) and the surrounding chamber (60) wall .

18. A device according to claim 16 or 17, characterized in that the free volume of said chamber (60) excluding the volume of the body (61) is larger than the volu- me of the reciprocating quantity of said first medium.

19. A device for carrying out thermal treatment in a body cavity or duct, the access path of which is narrow, in particular the prostate, comprising an elongate and hollow application catheter (6) intended to be inserted into said cavity or duct comprising a centrally located, heat-releasing element (19,79), which is surrounded by an elongate housing (20,77), a flexible and/or elastic balloon (2,63) surrounding said housing in a liquid-tight manner, further including means (10,75) for supplying energy to the heat-releasing element (19,39) and an axially operating inlet passage (27,95) at the proximal part of the housing (20,77), an outlet (22,54,93) from the housing (20,77) being arranged for the supply of a first heat-transmitting medium under pressure for expansion of the flexible balloon (2,63) to exert, under heating, pressure on surrounding walls of said cavity or duct, further comprising a viewing opening (5) located in said catheter (6) proximal to the balloon (2,63) for visual access to the exterior of said catheter (6) by accomoda- ting an endoscope therein, characterized by means (30) allowing, within said catheter, entrance of a second medium for irrigation of the endoscope lens, to pass said opening (5) and by means (85) acting to provide a reciprocating motion to a quantity of said first medium, said motion being transferred via the inlet passage (95) to the interior of said housing (20,77) and of said balloon (2,63) to agitate or circulate said first medium therein, and further characterized by a chamber (60) positioned in said passage (27,95) at the proximal end of said housing, and by a body (61) placed in said chamber (60) and movable between the distal and proximal ends of said cham- ber (60) while allowing a restricted flow of heat- transmitting medium aroung and/or through said body (60) for filling and emptying the balloon (2), said body (61) moving back and forth within said chamber (60) due to said recirpocating motion.

20. A device according to claim 19, wherein said restricted flow takes place via a circumferential play between said body (61) and the surrounding chamber (60) wall .

21. A device according to any one of claims 16 to 20, characterized in that said body (61) is made of a material of low heat conductivity, such as a polymer.