WO1999008634A1

WO1999008634A1 - Device for heat treatment

Info

Publication number: WO1999008634A1
Application number: PCT/SE1998/001457
Authority: WO
Inventors: Hans I. Wallsten
Original assignee: Wallsten Medical SA
Current assignee: Wallsten Medical SA
Priority date: 1997-08-19
Filing date: 1998-08-11
Publication date: 1999-02-25
Anticipated expiration: 2000-02-19
Also published as: SE9702984D0; AU8654898A

Abstract

A device for carrying out heat treatment in a body cavity or duct having a narrow access path, comprising an elongate distal section (103), and a heat releasing element (119) which is accommodated in an elongate housing (129), a flexible and/or elastic balloon (137) surrounding said housing in a liquid-tight manner. Further including an axially operating inlet passage (135) at the proximal part of the housing (129), and at least one outlet (133), for the supply of heat-transmitting medium. Further including means (25) to agitate or circulate said medium therein, characterized by a chamber (150) positioned in said passage (135) at the proximal end of the housing (129) and by a body (151) placed in said chamber (150). The body is movable between the distal and proximal ends of said chamber (150) while allowing a restricted flow of medium around and/or through said body (151) for filling and emptying the balloon (137).

Description

DEVICE FOR HEAT TREATMENT

Field of the invention

The present invention relates to devices for carrying out heat treatment in a body cavity or duct which has a narrow access pathway. The device is quite generally constituted by an applicator comprising an inflatable balloon in which a heated medium is agitated or circulated.

Background of the invention Hyperthermia is a form of heat treatment which has been mainly used for the treatment of malign tumors, and such treatment is normally performed at a relatively low temperature, such as about 43-45°C. It has also been suggested to treat certain benign or malign diseases in body cavities by necrosis at considerably higher temperatures. For the treatment of disorders in body cavities or ducts with narrow access pathways, such as the prostate, the bladder neck, the bladder and the uterus, it has been suggested to use balloon catheters of different designs, where a deflated balloon at the distant end of a catheter is introduced into the cavity or duct subject to treatment and is then inflated by a heating medium, usually a liquid. Heating means arranged in the balloon then heat the medium to a certain temperature, and the treatment temperature and time is selected to create necrosis or cauterization of the diseased tissue. Such apparatus for effecting thermal cauterization of for example the human uterine endometrium is disclosed in EP 0 433 376 to Neu- wirth. In such apparatus the heating medium is not circu- lated within the balloon, and this results in the drawback that the heat will not be evenly distributed to the surrounding body tissue resulting in uneven necrosis of the organ subject to treatment. It has also been suggested to thermally treat the prostate by circulation of a hot liquid through an inflated balloon, the hot liquid being provided from the exterior with a supply of heated fluid. To protect the narrow access pathways, such as the urethra in case of treating the prostate or bladder, there is provided for a special thermal insulation surrounding the different passage ways for the hot liquid. Such techniques are disclosed in US patent 5,257,977 to Eshel. However, also this technology is associated with draw-backs, since higher treatment temperatures above about 60-65°C will not be conceivable because of a pronounced risk for heat damages of the urethra. Higher temperatures are, however, desirable, since this could significantly reduce the treatment time necessary.

US patent 5,571,153 to allsten describes a device for thermal treatment of body cavities or ducts with narrow access pathways, such as uterus or prostate. This device is based on the generation of an oscillating pressu- re resulting in internal circulation of the heating medium within the balloon. This safequards even treatment resulting from an even temperature over the entire treatment area. However, at higher treatment temperatures the heat will be distributed backwards in the instrument rea- ching sensitive areas of the body duct, and this will impart a limitation with regard to the level of temperature and with regard to possible reduction of the diameter of the catheter.

Summary of the invention

The present invention has for a main object to eliminate the disadvantages associated with the prior art devices for the treatment of disorders in body cavities or ducts having narrow access pathways. The main object of the present invention is to provide a device enabling heat treatment at high temperatures to create necrosis or cauterization of diseased tissue without imparting risks to delicate tissues along the access pathway.

Another 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 the catheter.

Yet another object of the invention is to provide a device enabling intensive heating during treatment coup- led with even distribution of heat to the organ to be treated.

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

Still another object of the invention is to provide a device where the heating medium can be circulated or agitated inside the balloon to ensure even heat distribution during treatment. For these and other objects which will be clear from the following disclosure the invention provides for a device for carrying out heat treatment in a body cavity or duct having a narrow access pathway, said device comprising an elongate distal section intended to be inserted into said cavity or duct and including a centrally located heat releasing element which is accomodated in an elongate housing. Further comprising a flexible and/or elastic balloon surrounding said housing in a liquid- tight manner, and further including means for supplying energy to said element and an axially operating inlet passage at the proximal part of the housing, at least one outlet from the housing being arranged for the supply via the inlet passage of heat-transmitting medium under pressure for expansion of the balloon to accomodate to and to exert, under heating, a controlled pressure on surrounding walls of said cavity or duct. The device according to the invention further includes means acting to provide a reciprocating motion to a quantity of pressurized medium, said motion being transferred via the inlet passage to the interior of said housing and said balloon to agitate or circulate said medium therein. The device according to the invention is characterized by a chamber positioned in the inlet passage at the proximal end of the housing, and further characterized by a body placed in said chamber and movable between the distal and proximal ends of said chamber while allowing a restricted flow of medium around and/or through said body for filling and emptying the balloon, said body moving back and forth within said chamber due to said reciprocating motion.

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. The restricted flow of heating medium permitted by the body positioned in the proximally placed chamber can either take place via a circumferential play between the body and the surrounding chamber wall or can be provided by at least one axial passage through said body, or both. In a preferred embodiment the device according to the invention is characterized by at least one first backvalve arranged in association with an inlet for the heating medium arranged in the housing on the other side of the element relative to the outlet, and by a partition placed between the inlet and the element or between the element and the outlet, respectively, to form a chamber which is provided with an axial aperture or opening containing a second backvalve which acts oppositely to the first backvalve placed in the inlet. In this embodiment the means for the flow of the heating medium in an internal circuit is arranged to provide a reciprocating movement of a small quantity of the heating medium enclosed in the inlet passage 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. In this manner circulation of the heating me- dium in a closed circuit inside the balloon will be provided.

In an alternative embodiment of the device of the invention the elongate housing can be provided with several openings allowing access via the inlet passage to the interior of the balloon. In this manner said means providing reciprocating movement provides agitation of the heating medium inside the balloon.

The means for providing a reciprocating movement of a small quantity of the heating medium can comprise a re- ciprocating piston or membrane.

In order to avoid unnecessary impacts by the movable body within the chamber the free volume of said chamber, i.e. excluding the volume of the movable body, can be larger than the volume of the reciprocating quantity of pressurized or heating medium. Said free volume of the chamber need only be somewhat larger than the volume of the reciprocating quantity of pressurized medium since excess of volume only tends to enlarge the instrument without resulting in any further advantage. In a preferred embodiment of the device according to the invention the distal end of the housing is attached to the balloon. In this embodiment it is preferred to arrange a drainage valve positioned at the distal end of the housing which is operable from the outside for the drainage of gas from the interior of the balloon in connection with the filling of the balloon with heating medium.

In a particularly preferred embodiment of the device according to the invention the proximal end of the bal- loon is sealed aginst and around the proximal end of the housing, and the device contains a displaceable sleeve surrounding said end of the balloon. This enables selec- tion of the proper active length of the balloon for adaptation to body organs or ducts of varying size. As an alternative said sleeve can be axially displaceable so as to enable adjustement of the active length of the balloon for such adaptation.

In a particular embodiment of the device according to the invention said device can be provided with a viewing opening located at the proximal end of the housing and proximal to the balloon. Such opening enables visual access to the exterior of said distal section to facilitate positioning of the device.

In such embodiment the elongate distal section may accomodate an endoscope for visual inspection of the positioning of the device. According to a preferred embodiment of the device of the invention said balloon can be constituted by a double-layered balloon comprising an inner elastic and liquid-tight layer, and an outer layer of limited elasticity. According to a special embodiment of such balloon it can be designed as a triple-layered balloon comprising said inner elastic layer, an intermediate layer of limited elasticity corresponding to said outer layer, and an outer elastic layer.

Layers of limited elasticity may be comprised by braided or woven tubes, the filaments of which have limited elasticity, at least in a circumferential direction. As an alternative such layer of limited elasticity may be comprised of a winding of a filament of limited elasticity.

Brief description of the drawings In the drawings :

Figures 1 and 2 illustrate the state of the art according to US patent 5,571,153, of which the present in- vention constitutes important developments and improvements; Figure 3 shows diagramatically a section through the distal section of an embodiment of the device according to the invention;

Figure 4 shows a similar section of another embodi- ment of the device of the invention;

Figure 5 is a diagrammatic sideview illustration through the distal section of an embodiment of the device according to the invention;

Figure 6 illustrates circular sections along lines II-II and I-I of figure 5;

Figure 7 illustrates a section through a triple- layered balloon or enclosure in deflated and inflated state, respectively; 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 6.

Detailed description of the invention

In order to fully understand the principles accor- ding to which the device of the present invention operates it is necessary to briefly describe the prior art as disclosed in US patent 5,571,153. Figures 1 and 2 of the drawings correspond to drawing figures 1 and 2 of said US patent and are used for this purpose. The device described in figures 1 and 2 includes a heat applicator 1 with a distal part 3 to be inserted in a body cavity, for example the uterus, and a proximal part 7 with connecting means to an electric source 13 supplying an electric current via wires 15 to a central body 17 containing a heat-emitting element 19. Furthermore, the applicator is provided with means 23 for connection to an apparatus 25 for the generation of oscillating pressure impacts to the inlet passage 35 filled with a pressurized liquid from a liquid source 11. In the embo- diment shown apparatus 25 operates through a reciprocating piston. The central body 17 is surrounded by an expandable balloon 37 and comprises a housing 29 provided with apertures 31 and 33.

Figure 2 shows in detail a system for effective heat transfer from the elements 19 to the mucosa of the uterus. Apertures 31 act as radial inlets for a pressuri- zed liquid to a valve housing 32 communicating with the inlet passage 35 and the space between central body 17 and balloon 29, as well as canals 21 in the element 19. Apertures 33 act as outlets for the pressurized liquid communicating with canals 21 and the space between the central body 17 and the balloon 37. Back valves 49 are arranged to close apertures 31 at over-pressure and opening at sub-pressure. A disc valve 47 is arranged to close at over-pressure and open at sub-pressure.

Element 19 can be of any type operated by electric current and is connected to a supply of electric current preferably not exceeding 24V from a safety point of view. Another requirement is that the temperature necessary for the treatment can be maintained but not exceeded, which can be provided by suitable means not shown. It is appreciated that under the influence of the oscillating pressure shocks, a powerful and effective circulation in an internal flow circuit of liquid at a given pressure will be provided in the distal part 3 without hot liquid passing the inlet passage 35 to con- necting means 23. The inlet passage 35 during the circulation only serves as a communication conduit for transmitting the oscillating pressure and liquid movement provided by the pump apparatus 25. Therefore, the passage 35 can have a small diameter and therefore space is admitted for the heat insulation 26 surrounding the intermediate part 5 of the catheter.

When for example treating the uterus it is particularly the narrow cervix duct which has to be protected from excessive heating. Suitable temperatures for the treatment of uterus with a device according to figures 1 and 2 of the drawings are about 70°C, and the diameter of the catheter should not exceed 7-8 mm. The normal diame- ter of the cervix canal is about 3-5 mm and it is therefore necessary to dilate the canal before the catheter is introduced. A dilation of 6-7 mm can easily be made but a dilation of about 10 mm or more can be painful and could require deeper anaesthesia.

As indicated earlier there is often desirous to be able to increase the treatment temperature to allow a reduction in treatment time. It is also desirable to be able to reduce the diameter of the catheter, which in many cases would allow treatments under local anaesthesia on an outpatient basis in a doctor's office.

Although the devices provided with internal circulation as disclosed in US 5,571,153 have certain advantages with regard to the protection of the narrow pathways from heat as described above, there is a limitation when it comes to an increase of the treatment temperatures and/or a reduction in diameter of the catheter. This can be explained with reference to figures 1 and 2.

During treatment the circulating liquid enclosed in the balloon 37 is hot while the oscillating liquid in the passage 35 is cold. During oscillation and heating, however, a certain volume of liquid will be brought to move forward and backward which means that a quantity of cold liquid enclosed in the distal part of the passage 35 will be forced into the housing at every positive stroke of the pump and a quantity of hot liquid will be pulled into passage 35 at every negative stroke of the pump. Due to turbulence there will be a mixture of hot and cold liquid enclosed in the distal part of the passage 35. This is the reason why this section of the passage needs to be protected by heat insulation 26. Consequently, any attempt to increase the treatment temperature will give a higher temperature in the distal part of passage 35, which will require thicker insulation thereby increasing the diameter. Correspondingly, if a smaller catheter diameter is desired the temperature must be decreased.

Figure 3 illustrates an embodiment of the device ac- cording to the present invention which constitutes an improvement of the devices disclosed in US patent 5,571,153 and in particular the embodiment shown in figure 2. A heat applicator corresponding to applicator 3 in figure 1 is designated 103 and is intended to be connected to an electric source, a means for introducing a pressurized liquid and a means for the generation of oscillating pressure impacts. These means are not shown in the drawing but have been described in connection with figure 1. Heat-emitting elements 119 are enclosed in a central body constituted by a housing 129 provided with apertures 131 and 133.

Apertures 131 act as radial inlets for a pressurized liquid to a valve space 132 communicating with an inlet passage 135 and a space between housing 129 and balloon 137, as well as passages or canals 121 in the element 119. Apertures 133 act as outlets for the pressurized liquid communicating with canals 121 and the space between the housing 129 and the balloon 137. Back valves 149 are arranged in association with apertures 131 to close same at over-pressure and to open same at sub-pressure. A disc-valve 147 is arranged to open at over-pressure and to close at sub-pressure.

A chamber 150 is arranged at the proximal end of the valve housing 132 or an extension thereof and stands in communication with passage 135. For practical reasons housing 129, as well as valve housing 132 and chamber 150 have circular cross-sections. A piston or movable body 151 is located in chamber 150. This body 151 can move freely axially forth and back due to the fact that it has a diameter somewhat smaller than the inner diameter of chamber 150. In the center of body 151 an axial opening or hole 152 has been provided to allow for the passage of electrical wires 115 to the heating element 119. The chamber 150 ends proximally at 153 and the body 150 can only move between this proximal end 153 and a stop 154 arranged in housing 132. If the body 151 has a thickness of t mm and the chamber 150 a length of 1 mm the body can move freely for a total length of 1-t mm.

If the device according to figure 3 is filled with pressurized liquid acting as a heating medium and is con- nected to an apparatus for the generation of oscillating impacts as described in connection with figures 1 and 2, the piston 151 will start to oscillate under the influence of the pressure shocks and movement of the oscillating liquid in passage 135. In figure 3 the movable body 151 is shown in its end position butting end 153. If it is assumed that the oscillating movement of the liquid starts with a positive stroke of the oscillator, a certain amount of liquid starts to move creating an over-pressure. The body 151 will start to move towards the stop 154 leaving a space in chamber 150 which will subsequently be filled with a cold liquid from passage 135. Correspondingly, the body 151 will push an amount of hot liquid out into the valve housing 132 and further through the elements 119 and the disc-valve 147 through apertures 133 and out in the space between the balloon 137 and the housing 129 somewhat increasing the size of the balloon. As mentioned earlier, body 151 has a somewhat smaller diameter than the chamber 150. This is important because it creates passage for a limited amount of heating liquid, which will be explained later. During its positive stroke body 151 will move axially providing a space filled with cold liquid the volume of which corresponds to the total volume of the positive stroke reduced by the volume of liquid which has passed body 151.

When the oscillating pump generates a negative stroke, body 151 will reverse and move in direction towards the chamber 153 filling the left part of the space 150 with hot liquid and emptying the right part of said space of cold liquid.

The possibility for the liquid to pass the body 151 is important for several reasons. One is to allow pressu- re changes at filling or emptying the liquid in the applicator using device 11 in figure 1. Another is to make it possible to perform the necessary pressure changes during a treatment. In the description of the movement of body 151 given above it was assumed that the starting point for the body at a positive stroke was the right-hand position shown in figure 3. In case body 151 had been in a position to the left an important pressure would have been created when the body stopped at 154 thus allowing a more important flow to pass across the body. At the next negative stroke the body can start from a "correct" left-hand position. The arrangement with a play between body and surrounding chamber wall will thus enable correction of the position of the body. To avoid that the body 151 is repeatedly hitting the stop 154 or the end 153 when oscillating it is preferred that the volume of the chamber 150 excluding the volume of the body 151 is somewhat larger than the volume of the stroke of the oscillating pump. Experience has shown that for an effective heat transfer from the heater 119 through the balloon 137 to the surrounding tissue a certan minimum quantity of the heat-transmitting liquid must be circulated. The quantity is depending on the stroke volume and the frequency. As an example of an effective heat transfer with a balloon volume of about 5 ml a circulated quantity of about 0.2 to 2.0 ml per second can be used. It is not a problem to design a pump in the form of a piston or a membrane to create an oscillating volume per second corresponding to these figures.

There is, however, a limit for achieving an effective circulation inside the balloon 137 at higher frequences than about 15-25 strokes per second, e.g. because of the back-valves in the system which loose efficiency at higher frequences. It is therefore preferred to select a relatively high stroke volume, such as about 0.025-0.1 ml at a relatively low frequency, such as 5-25 strokes per second. As mentioned earlier the maximum outer diameter of the applicator should not exceed 6-7 mm to allow easy insertion. This means that there is a restriction in the diameter of the body 151. Assume that a diameter of 4 mm is feasible. This results in a stroke volume of 0.06 ml at a displacement of 5 mm. Such displacement with such a diameter will not be operable using a diaphragm to prevent mixing of hot liquid and cold liquid. Furthermore, the use of a diaphragm does not allow passage of liquid into the interior of the balloon for filling same.

Experiments with devices according to the invention, such as the embodiment shown in figure 3, have confirmed the effect of using an oscillating movable body. Temperatures have been measured on different parts of the device with and without such movable body. For example, a catheter with a diameter of 6 mm was heated at a temperature of 75°C measured on the surface of the balloon. The power mainly due to heat losses from the balloon was measured to about 14Watt. The temperature distal to the dotted line A-A in figure 3 along the catheter shaft was between 40 and 45°C. The surface of the bypass area over the movable body was 10% of the surface of the body and this was sufficient to inflate, deflate and otherwise adjust the balloon pressure in a reasonable period of time. Body 151 was then removed and the corresponding temperature was 50-60°C along the catheter.

The feature of the present invention thus enables the creation of a sharp limit between a hot and a cold zone as indicated in figure 3. The body should have a suitable thickness, such as at least about 3 mm and preferably be made from a material of low heat conductivity, such as a porous, non- absorbing plastic.

In figure 4 there is shown an alternative embodiment of the device according to the invention. Also in this case the device is intended to be connected to an apparatus for the generation of oscillating impacts. The device of figure 4 differs from that of figure 3 in that there are no means for internal circulation such as by using back-valves. In this embodiment housing 160 is provided with several holes 161 acting as both inlets and outlets for the heat-transmitting liquid. The shock waves from the oscillating generator are transmitted via body 151 to the liquid in the housing 160, and at each positive stroke hot liquid will be pressed out through the holes 161 creating turbulence inside the balloon 137 and the housing 160. No circulation but an effective agitation can be achieved and has the advantage that the device has a simpler and cheaper design. The embodiment of figure 4 is further provided with a drainage valve 164 for the escape of air when filling the device with heat-transmitting liquid. Trapped air can be released through an outlet 162 by inserting a pin through an opening 163 to lift a valve element 165 from its seat by compressing the spiral spring 164.

The device shown in figure 4 is further provided at the proximal end of the balloon 137 with a sleeve 170 which is axially displacable. The balloon 137 is sealed at is proximal end 172 to the center shaft 173. The position of the distal end 171 of sleeve 170 will, therefore, determine the active length of the inflated balloon 137. This enables adjustment of the length of the balloon, which is an advantage in for instance thermal treatment of uterus. A better adaptation to the uterus cavity can be achieved and expansion of the hot balloon in the cervix canal can be avoided. Sleeve 170 can, after adjustment, be fixed against the catheter shaft 173 by means known per se but not shown in the drawing.

As an alternative sleeve 170 can be replaced by a set of sleeves of varying length for proper selection of active balloon length. Another alternative is constituted by the application of a simple tape or similar means to provide the desired active balloon length.

Figure 5 shows in detail the distal part of the applicator according to another embodiment of the inven- tion. The balloon 202 is flexible and sealed at least at its proximal end to the distal end of the housing 220. Inside the balloon 202 a heating means 221 is arranged illustrated as a resistor wire. An outlet opening 253 is arranged distal to the heating means 221 and is associated with a back valve 257 allowing outlet but preventing inlet through said opening 253. The back valve 257 is arranged in a space which through outlets 254 is in fluid connection with the interior of the balloon 202. At the other end of the housing 220 inlet openings 255 with associated back valves 256 are arranged. Back valve 256 allows entrance from the interior of the balloon 202 into the interior of housing 220.

The device according to figure 5 operates by inter- nal circulation in the same way as described in connection with figure 2. Accordingly, such internal circulation is provided by a means 25 providing reciprocating motion of the medium used for filling and heating of the balloon. At the proximal end of the distal section of the device an opening 205 is provided through which by the use of an endoscope 204 through an endoscope lens 223 the practitioner can position the device properly in the target organ or duct, so that for example a sensitive area, such as an external sphincter, can be placed opposite to the applicator part between the distal end of the balloon and the opening 205.

A tube 225 is connected to valve 13 (fig. 1) for inflating and deflating the balloon with the liquid serving as heat-transmitting fluid for heat released from heating means 221. The distal end of tube 25 is attached to a partition 38, which contains an inlet/outlet hole for the liquid in the tube 225.

In the embodiment shown in figure 5 a space 260 is arranged distal in relation to the wall 238 of housing 220. A movable body 261 can freely move longitudinally back and forth in space 260. The applicator is connected to an oscillating pump according to the principle shown in figure 1 for an effective circulation of the heating medium. Because of the oscillating movement of the liquid in tube 25 body 261 will also oscillate. At the end of each withdrawal stroke of the pump body 261 will stop in a position corresponding to the dotted lines 263. The volume of space 260 excluding the volume of the body 261 should be about the same or somewhat larger than the volume of one stroke of the oscillating pump.

In the embodiment shown in figure 5 an irrigating liquid is introduced proximally of opening 205 as shown by arrow 233. As a preferred embodiment also cooling can be provided. Thus, a horisontal wall 30 is arranged wit- hin the conduit leading to the proximal part of housing 220 and creates an upper space 231 and a lower space 232. The cooling liquid is introduced to the lower space 232 and flows in the direction of arrow 233. The wall 230 ends at 234 allowing the liquid to mount and return in the opposite direction as shown by arrows 235 and 236. The cooling keeps the inner walls of the proximal parts of the distal section cool and particularly the area close to the hot balloon 202 and the separating wall 238. Figure 6 shows the cross-sections I-I and II-II, re- spectively, and particularly how the wall 230 creates an upper space 231 and a lower space 232. Cables and wires 237 for the heater 219 are shown and the arrangement allows temperature control in a manner not shown.

Figure 8 shows an alternative arrangement to that shown by section I-I of figure 6. 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 6. According to the embodiment of the invention shown in figures 5 and 6 there is created a hot zone at the distal part of the applicator including the inflated part of the balloon 202 and a cool zone proximal to the inflated balloon 202. Assisted by the endoscope 204,205 the practitioner can keep the applicator in such a position that sensitive tissue is protected from thermal damage while the thermal treatment at a high temperature is performed around the active part of the balloon. According to this embodiment of the invention the cooling liquid will also on its return serve as an irrigating liquid for the endoscopic lens 223. Figure 4 shows an arrangement, whereby the active length of the balloon can be adjusted using a sleeve 170 at the proximal part of the balloon. Figure 5 shows a similar arrangement for the adjustment of the active length of the balloon but in this case through the use of means positioned at the distal end of the balloon 202. The distal end 243 of the balloon 202 is liquid-tight sealed to housing 220. A part of the distal section 244 of the balloon cannot thereby expand when the balloon is inflated as it is surrounded by an axially displaceable. end piece in the form of a cap 245. The dot- ted lines show the outermost end position of cap 245 and the distal end of the balloon. The cap can be maintained in a fixed position by locking means not shown. As an alternative the cap can be replaced by a sleeve or a set of sleeves of varying length for obtaining the desired acti- ve length of the balloon 202. In certain applications, such as in the heat treatment of the prostate, 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 elas- ticity. Irrespective of the shape of the cross-section the drawback of using preformed flexible thin tubes with low elasticity is that such deflated balloon has wrinkles causing problems at insertion of the device. An alternative solution is to use a multilayer balloon consisting of layers of an elastomer, such as silicon, and a surrounding elastic material which can be extended only to a certain upper limit. A suitable material of limited ex- pandability is an elastic clothing used for socks and stockings which is made by a so called stretchible 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 expansion when the nylon filament is stretched. A clothing woven in the form of a sleeve or tube has a certain diameter in released form and can be expanded to a maximum predetermined diameter and resist high pressures.

It is preferred to surround such a layer of material of limited elasticity by an outer layer of an elastomer, such as silicon.

Figure 7 illustrates cross-sections of such a multi- layer 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 direc- tion. As an alternative said layer of limited elasticity may be comprised of a winding of a filament of limited 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 limited 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 vary- ing along its length, such as conical configuration. This can be done by placing the inner elastic layer onto a core of corresponding configuration. There are many variations of the invention as described and this invention should be limited solely by the scope of the following claims.

Claims

1. A device for carrying out heat treatment in a body cavity or duct having a narrow access path, comprising an elongate distal section (103) intended to be inserted into said cavity or duct and including a centrally located, heat releasing element (119) which is accomodated in an elongate housing (129), a flexible and/or elastic balloon (137) surrounding said housing in a liquid-tight manner, further including means (115) for supplying energy to said element (119) and an axially operating inlet passage (135) at the proximal part of the housing (129) , at least one outlet (133) from the housing (129) being arranged for the supply via inlet passage (135) of heat- transmitting medium under pressure for expansion of the balloon (137) to exert, under heating, pressure on surrounding walls of said cavity or duct, further including means (25) acting to provide a reciprocating motion to a quantity of pressurized medium, said motion being trans- ferred via the inlet passage (135) to the interior of said housing and of said balloon (137) to agitate or circulate said medium therein, characterized by a chamber

(150) positioned in said passage (135) at the proximal end of the housing (129) , and by a body (151) placed in said chamber (150) and movable between the distal and proximal ends of said chamber (150) while allowing a restricted flow of medium around and/or through said body

(151) for filling and emptying the balloon (137), said body (151) moving back and forth within said chamber (150) due to said reciprocating motion.

2. A device according to claim 1, whrein said restricted flow takes place via a circumferential play between said body (151) and the surrounding chamber wall.

3. A device according to claim 1, wherein said body (151) is provided with at least one axial passage allowing said restricted flow.

4. A device according to any one of claims 1 to 3, characterized by at least one first back valve (149) arranged in association with an inlet (131) for the medium arranged in housing (129) on the other side of element (19) relative to said outlet (133), and by a partition (143) placed between said inlet (131) and element (119) or between said element (119) and outlet (133), respectively, forming a chamber (139) and being provided with an axial aperture containing a second back valve (147) which is oppositely acting relative to a first back valve (149) placed in inlet (131), said means (25) for the flow of the medium in an internal circuit being arranged to provide a reciprocating movement of a small quantity of the pressurized medium enclosed in the inlet passage (135) of the device after expansion of the balloon (137), 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.

5. A device according to any one of claim 1 to 3, characterized by an elongate housing (160) provided with several openings (161) allowing access via inlet passage (135) to the interior of the balloon (137), whereby said means (25) provides agitation of said medium inside the balloon (137) .

6. A device according to any one of the preceding claims, wherein said means (25) comprises a reciprocating piston or membrane.

7. A device according to any one of the preceding claims, characterized in that the free volume of said chamber (150) excluding the volume of said body (151) is larger than the volume of the reciprocating quantity of pressurized medium.

8. A device according to any preceding claim characterized in that the distal end of said housing (129; 160) is attached to the balloon (137).

9. A device according to claim 8, characterized by a drainage valve (164) positioned at the distal end of said housing and operable from the outside for the drainage of gas from the interior of the balloon (137).

10. A device according to any one of the precding claims, characterized in that the proximal end (172) of the balloon (137) is sealed against the proximal end of the housing (160) and is surrounded by a sleeve (170) , whereby the active length of the balloon can be selected.

11. A device according to claim 10, wherein said sleeve (170) is axially displacable, whereby the active length of the balloon can be adjusted.

12. A device according to any preceding claim, characterized by a viewing opening located at the proximal end of said housing proximal to the balloon for visual access to the exterior of said distal section to facili- tate positioning of the device.

13. A device according to claim 12, characterized by means (230,232) allowing, within said distal section

(103), entrance of a second medium to pass said opening for irrigation of the endoscope lens.

14. A device according to any preceding claim, characterized in that said body (151) is made of a material of low heat conductivity, such as a polymer.