Abstract:
An inlet flow of heat exchange fluid flows from an inflow housing inlet section, and through an inflow housing main section. It then flows through an inlet fluid passageway formed between an inner balloon and a discharge tube. The flow continues around a distal end of the inner balloon, thus becoming an outlet flow of the heat exchange fluid which is directed through an outlet fluid passageway formed between the inner balloon and an outer balloon, then through an outflow housing main section and finally discharged through an outflow housing outlet section. The inner balloon is in a position offset from the central axis of the catheter. The offset relationship enhances the fluid dynamic properties of the catheter. It provides an increased turbulence, which, in turn, maximizes the heat exchange efficiency.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to urological warming and cooling devices and more particularly to a warming catheter and method of warming the urethra of a patient during ablative surgery. The apparatus is particularly useful in cryosurgery to prevent damage to tissues surrounding a surgical site from the extremely cold temperatures employed therein. The apparatus is especially useful during transperineal cryoablation of the prostate gland in human males to maintain the temperature of the urethral tissues and thereby prevent urethral sloughing. The apparatus may also have utility where it is desired to lower the temperature of surrounding tissues, such as during laser ablation. 
   2. Description of the Related Art 
   Cryosurgical probes are used to treat a variety of diseases. The cryosurgical probes quickly freeze diseased body tissue, causing the tissue to die after which it will be absorbed by the body, expelled by the body or sloughed off. Cryothermal treatment is currently used to treat prostate cancer and benign prostate disease, breast tumors and breast cancer, liver tumors and liver cancer, glaucoma and other eye diseases. Cryosurgery is also proposed for the treatment of a number of other diseases. 
   The use of cryosurgical probes for cryoablation of the prostate is described in, for example, Onik,  Ultrasound - Guided Cryosurgery, Scientific American  at 62 (January 1996). Cryosurgical probe systems are manufactured by present assignee, Endocare, Inc. of Irvine, Calif. In cryosurgical ablation procedures generally several cryosurgical probes are inserted through the skin in the perineal area (between the scrotum and the anus), which provides the easiest access to the prostate. The probes are pushed into the prostate gland through previously placed cannulas. Placement of the probes within the prostate gland is typically visualized with an ultrasound imaging probe placed in the rectum. The probes are quickly cooled to temperatures typically below −120° C. The prostate tissue is killed by the freezing, and any tumor or cancer within the prostate is also killed. The body absorbs some of the dead tissue over a period of several weeks. However, other necrosed tissue may slough off and pass through the urethra, often causing undesirable blockage. Thus, it is often desirable to avoid cryoinjury to the urethra during cryoablation of the prostate. This may be done by placing a warming catheter in the urethra and continuously flushing the catheter with warm fluid to keep the urethra from freezing. 
   Devices for warming the urethra have been available for quite some time. In 1911, U.S. Pat. No. 1,011,606 issued for an “Appliance For Subjecting Portions Of The Human System To Heat Or Cold.” This device was a coaxial dual lumen catheter intended for the application of therapeutic cooling or heating to the urethra and bladder. Devices for warming other body parts have also been proposed, such as U.S. Pat. No. 4,244,377, issued Jan. 13, 1981 to Grams entitled “Ear Probe For Use In Closed-Loop Caloric Irrigation”, which shows a coaxial dual lumen cannula intended for the application of therapeutic heating inside the ear. 
   U.S. Pat. No. 5,437,673, issued on Aug. 1, 1995 to Baust, et al., entitled “Closed Circulation Tissue Warming Apparatus and Method of Using the Same in Prostate Surgery” illustrates use of a urethral warming catheter which is used to protect the urethra from cryothermal damage during cryosurgical treatment of the prostate for benign prostate hyperplasia. The Baust patent discloses a coaxial three lumen catheter in which warm saline passes through an outside lumen and is returned through a coaxial second lumen. A third lumen is a urinary drainage lumen centrally disposed within the other two lumens. The catheter is used to heat the urethra while the prostate is being frozen with cryosurgical probes. 
   A very similar device to that disclosed in U.S. Pat. No. 5,437,673 is disclosed in U.S. Pat. No. 5,624,392, issued on Apr. 29, 1997 to Saab, entitled “Heat Transfer Catheter and Methods of Making and Using Same.” 
   U.S. Pat. No. 5,257,977, issued on Nov. 2, 1993 to Eshel, entitled “Technique for Localized Thermal Treatment of Mammals,” shows a catheter that delivers heated saline flow to provide therapeutic hyperthermia treatment of the prostate. Like the Baust patent, Eshel shows a three lumen catheter with a centrally located urinary drainage lumen. 
   Still other devices have been described for importing fluid into the body and allowing a means for removing fluid from the body. One such device is described in U.S. Pat. No. 3,087,493, issued Apr. 27, 1960 to Schossow, entitled “Endotracheal Tube”. Schossow describes a device employed to intubate the human trachea. The device is connected with ducts and/or tubes outside the patient for the purpose of, for example, drawing off from the patient&#39;s respiratory tract undesirable liquids and/or introducing beneficial liquids into the trachea. The device comprises an outer tube, which fits inside the patient&#39;s trachea, and a two layered inner tube. The lumen of the inner tube is open to be connected with devices or ducts through which suction may be applied or fluids injected into the trachea. The distal portion of the inner tube is vented with ports or openings that create a “sprinkler” effect inside the tube. 
   During cryoablation, the prostate tissue is killed by freezing temperatures in the cryogenic temperature range, typically −120° C. and below. The hot fluid used for the warming catheter is supplied at about 30° C. to 50° C. Warm fluid is pumped through the urethral warming catheter, such as the catheter described in Baust et al. Using this catheter, as the warm fluid travels the length of the urethral catheter disposed within the cryosurgically-cooled urethra, it is cooled by the surrounding freezing tissue. By the time the hot water has traveled from the bladder neck sphincter to the external sphincter, it has been significantly cooled by the surrounding frozen prostate. As a result, the urethral tissue near the bladder neck sphincter (near the hot water outlet) is heated more than the urethral tissue near the external sphincter, creating a strong thermal gradient in the prostatic urethra and an uneven heating effect. By the time the hot water reaches the external sphincter, it may have lost so much heat to the upper region of the urethra that it is not warm enough to protect the external sphincter from freezing. In order for the tissue at the bladder neck sphincter to be adequately warmed, hotter water must be pumped in, risking urethral damage due to scalded tissue, or more water must be pumped at higher rates and pressures, increasing the material requirements of the hot water supply system and the warming catheter. 
   U.S. Pat. No. 6,017,361, issued to Mikus et al, entitled “Urethral Warming Catheter,” discloses an improved method and means for maintaining the temperature of urethral tissues during cryoablation of the prostate gland and thereby eliminates or reduces the sloughing of dead cells into the urethra. Diffuser holes or ports, much like a “sprinkler,” are drilled into the inner tube of the warming catheter. The holes create an advantage over the prior art of achieving improved uniformity of fluid flow and temperature, utilizing a lower initial temperature and resulting in a more even application of thermal treatment to the urethral tissues. The apparatus may find additional utility in other areas of surgery where thermal treatment or maintenance of tissues is required with or without the capability of drainage. 
   SUMMARY OF THE INVENTION 
   In one broad aspect the present invention is a heat exchange catheter that includes an inflow housing assembly, an outflow housing assembly, a discharge tube, an inner balloon, an outer balloon, and flow separation means. The inflow housing assembly includes an inflow housing main section having a central axis; and, an inflow housing inlet section coupled to the inflow housing main section for providing an inlet flow of heat exchange fluid to the inflow housing main section, the inflow housing main section and the inflow housing inlet section having respective openings therein for providing for the inlet flow. The outflow housing assembly includes an outflow housing main section having a central axis which is along the central axis of the inflow housing main section. The outflow housing main section is coupled to the inflow housing main section. An outflow housing outlet section is coupled to the outflow housing main section for receiving an outlet flow of heat exchange fluid from the outflow housing main section. The outflow housing main section and the outflow housing outlet section have respective openings for the inlet flow and the outlet flow. The discharge tube is positioned within respective openings of the inflow housing assembly and the outflow housing assembly, the discharge tube being positioned along the central axis. The inner balloon is positioned about the discharge tube and coupled to the outflow housing assembly. The inner balloon is in a position offset from the central axis. The outer balloon is positioned about the inner balloon and connected at a first end to the outflow housing assembly. A second end thereof is securely attached to a distal portion of the discharge tube. The inner balloon is shorter than the outer balloon. Flow separation means for separating the inlet flow of heat exchange fluid from the outlet flow of warming fluid. During operation, the inlet flow of heat exchange fluid flows from the inflow housing inlet section, and through the inflow housing main section, then through an inlet fluid passageway formed between the inner balloon and the discharge tube, the flow continuing around a distal end of the inner balloon, thus becoming the outlet flow of the heat exchange fluid which is directed through an outlet fluid passageway formed between the inner balloon and the outer balloon, then through the outflow housing main section and finally discharged through the outflow housing outlet section. 
   The heat exchange catheter is particularly useful as a warming catheter for prostatic cryosurgical procedures where cryosurgical probes are used and it is desired to maintain the temperature of the urethral tissues to prevent urethral sloughing. 
   Offset positioning of the inner balloon, in contrast to any coaxial relationship of this inner balloon to the outer balloon and the discharge tube (such as disclosed in U.S. Pat. Nos. 5,437,673 and 5,624,392) has certain advantages. An offset relationship enhances the fluid dynamic properties of the catheter. It provides an increased turbulence, which, in turn, maximizes the heat exchange efficiency. 
   Furthermore, this offset positioning provides the ability to have a discharge tube of minimal thickness and thus enhanced flexibility, which is important, for example, for application in the urethra in which the catheter must be able to bend around the pubic bone when inserted through the urethra. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a first embodiment of the heat exchange catheter of the present invention. 
       FIG. 2  is a bottom plan view of the embodiment of  FIG. 1 . 
       FIG. 3  is a cross-sectional view taken along line  3 - 3  of  FIG. 2 . 
       FIG. 4  is an enlarged cross-sectional view of the invention. 
       FIG. 5  is a sectional view taken along lines  5 - 5  of  FIG. 4 . 
       FIG. 6  is a perspective view of the distal portion of the heat exchange catheter. 
       FIG. 7  is a perspective view of a second embodiment of the heat exchange catheter of the present invention. 
       FIG. 8  is a bottom plan view of the embodiment of  FIG. 7 . 
       FIG. 9  is a cross-sectional view taken along line  9 - 9  of  FIG. 8 . 
       FIG. 10  is an enlarged cross-sectional view of the second embodiment of the invention. 
       FIG. 11  is a sectional view taken along lines  11 - 11  of  FIG. 10 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings and the characters of reference marked thereon,  FIGS. 1-6  illustrate a first embodiment of the heat exchange catheter of the present invention, designated generally as  10 . The catheter  10  includes an inflow housing assembly, designated generally as  12  and an outflow housing assembly, designated generally as  14 . The generally cylindrical housing assemblies  12 ,  14  are coupled to each other and are serially positioned along a common housing assembly central axis  16 . An outer balloon  18  projects from the distal end of the outflow housing assembly  14 . A discharge tube  20  is also positioned along the central axis  16  and extends beyond the end of the outer balloon  18 . 
   As best seen with reference to  FIG. 4 , the inflow housing assembly  12  includes an inflow housing main section  22  and an inflow housing inlet section  24  coupled to the inflow housing main section for providing an inlet flow of warming fluid to the inflow housing main section. The inflow housing main section  22  and the inflow housing inlet section  24  have respective openings therein for providing for the inlet flow, designated by arrows  26 . In the embodiment shown, the inflow housing main section  22  and the inflow housing inlet section  24  together comprise an integral, molded plastic part. 
   The outflow housing assembly  14  includes an outflow housing main section  28 , which is along the central axis  16  of the inflow housing main section  22 . The outflow housing main section  28  is coupled to the inflow housing main section  22  via a divider element, designated generally as  30 . An outflow housing outlet section  32  is coupled to the outflow housing main section  28  for receiving an outlet flow of warming fluid from the outflow housing main section  28 , the outlet flow, designated by arrows  34 . The outflow housing main section  28  and the outflow housing outlet section  32  have respective openings for the inlet flow  26  and the outlet flow  34 . 
   The divider element (i.e. flow separation means)  30  includes a proximal axially oriented portion  36  secured to a distal end of the inflow housing main section  22  and to a proximal end of the outflow housing main section  28 . A radially inwardly extending portion  38  depends from a distal end of the proximal axially oriented portion  36 . The radially inward extending portion  38  is radially off center from the central axis  16 . A distal axially oriented portion  40  depends from the radially inwardly extending portion  38 . The distal axially oriented portion  40  is secured to a proximal end of an inner balloon  42  thus positioning the inner balloon  42  and its inner balloon central axis in an offset position from the housing assembly central axis  16 . The outflow housing main section  28  includes an axial extension  44 . The outer balloon  18  is secured between the outer surface of the axial extension  44  and strain relief element  48 . Although  FIG. 4  illustrates the inner balloon  42  being secured to the inner surface of the distal axially oriented portion  40  it may be secured in other locations such as the outer surface of the distal axially oriented portion  40 . 
   A LUER fitting  46  extends rearwardly from a proximal end of the inflow housing main section  22  for providing access to the discharge tube  20 . The discharge tube  20  may provide access for the discharge of bladder fluid or may, for example, provide access for a guide wire or endoscope. 
   The balloons  18  and  42  are preferably made from a flexible, relatively non-stretchable, polyester film such as polyethylene terephthalate (PET), outer balloon  18  having a fixed diameter upon introduction of fluid therein. Preferably, this diameter is about 22 French, which corresponds to the average diameter of the urethra in adult male humans. The length of the balloons may be on the order of, for example, from about 12 inches to about 24 inches. The inner balloon may have an outside diameter of about 0.162 inches and an inside diameter of about 0.160 inches. The outer balloon may have an outside diameter of about 0.284 inches and an inside diameter of about 0.281 inches. 
   The discharge tube  20  may be formed of, for example, a suitable plastic such as polyamide. It may, for example, have an outside diameter of about 0.107 inches and an inside diameter of about 0.058 inches. Therefore, the thickness of the discharge tube may be, for example, about 0.0245 inches. This is much thinner than present commercially sold products, having a thickness of about 0.052 inches. Thus, the discharge tube  20  of the present invention is much more flexible. 
   As protection against damage due to excessive flexing, a strain relief element  48  in the form of a length of heavier gauge plastic tubing is attached to the outflow housing assembly  14  by telescoping a portion of the tubing over the outer surface of barbed axial extension  44 . Strain relief element  48  extends a distance of approximately five centimeters beyond the end of axial extension  44 . 
   In a specific example of operation, to warm a urethra of a patient during cryosurgical ablative surgery, ablative devices are inserted into the prostate region of a patient. The heat exchange catheter  10 , operating as a warming catheter, is inserted through the patient&#39;s urethra at least to the bladder neck and generally into the bladder. Warming fluid is delivered through the catheter  10  during operation of the ablative surgical devices. The warming fluid is delivered into the bladder. The urethra is warmed by the warming fluid to preserve living tissue thereof. 
   The ablative devices are preferably cryosurgical probes such as manufactured and marketed by Endocare, Inc., of Irvine, Calif. Generally, six cryosurgical probes are used as well as four temperature probes. Alternatively, other ablative devices may be used, for example, radio frequency electrodes, laser fibers, microwave catheters, or high-intensity focused ultrasound. In such instances the heat exchange fluid is cool so as to prevent the urethra from the heating by the ablative elements. 
   Although not shown, the inflow housing assembly  12  receives heat exchanges fluid from a pump and warmer, which are, in turn, connected to a reservoir. The warming fluid should be supplied at temperatures sufficient cool so as to not thermally damage the urethra. Appropriate fluids include sterile water, physiological saline, and the like and should be such fluids as are biocompatible and physiologically benign in the event of inadvertent rupture of the balloons  18 ,  42 . 
   The warming fluid passes through the inflow housing assembly  12 , as shown by arrows  26 , and into the outflow housing assembly  14  within the inlet fluid passageway formed within the inner balloon  42 . As the flow reaches the distal end of the inner balloon it is turned, as indicated by arrows  50  (shown in  FIGS. 4 and 6 ), and is directed in the outlet fluid passageway formed between the outer balloon  18  and the inner balloon  42  as indicated by arrows  34 . It is then discharged through the outflow housing outlet section  32 . Thus, a closed fluid circulation path is provided as the fluid is returned to the reservoir. The countercurrent flow of incoming and outgoing fluid allows the warmer incoming fluid in inner balloon  42  to warm the cooler outgoing fluid in outer balloon  22 . The thermal exchange is even along the length of catheter  10 . Even though from the figures (e.g.  FIG. 5 ) it appears as if there may be some attachment of the outer balloon  18  and the inner balloon  42 , they are not attached, and indeed there is a generally a gap between the two balloons even in the proximity in which they appear to be very close to each other. 
   The entire apparatus of the catheter  10  may be constructed in larger or smaller sizes as needed depending on the criteria of patient and use. For example, a catheter  10  for use on a child will be smaller than that used on an adult. Similarly, a catheter  10  for use elsewhere in the body may be smaller or larger than that used in the urethra. 
   Referring now to  FIGS. 7-11 , another embodiment of the present is illustrated, designated generally as  52 . In this instance, the inflow housing assembly  54  includes an inflow housing main section  56  that comprises an inflow block. Similarly, the outflow housing assembly  58  includes an outflow housing main section  60  that comprises an outflow block. 
   The inflow block has a first axial extension  62  having a decreased diameter and a second axial extension  64  having a further decreased diameter. A mating surface is formed by the presentation of the first axial extension  62  being offset from the central axis  66 . An inner radial surface of the second axial extension  64  is secured to an outer surface of the inner balloon  68 . The outer balloon  70  may be secured to an outer surface of an axial extension  72  of the outflow housing main section  60 , as shown in this figure. Alternatively, it may be secured to an inner surface of the axial extension  72 . 
   A LUER fitting  74  is secured to and extends from a proximal end of the inflow housing main section  56  for providing access to a discharge tube  76 . In this embodiment, the inflow housing inlet section  78  and outflow housing outlet section  80  are separate pieces from their respective main sections  56 ,  60 . They are threaded into their positions relative to their associated main sections. The flow separation means in this embodiment is the material that forms the blocks  56 ,  60 . Inlet fluid passageways and outlet fluid passageways are provided within these blocks. 
   This embodiment operates in the same manner as that described above with respect to the first embodiment with inlet flow, designated by arrows  82 , passing through the inflow housing assembly  54 , around the distal end of the inner balloon as shown by arrow  84 . The flow thus becomes an output flow  86  that flows through the outflow housing assembly  58 . 
   Although the examples discussed above refer to the use of a warming fluid it is understood that if the ablative devices are for heating rather than for cooling, the heat exchange fluid would be a cooling fluid. 
   The heat exchange catheter may find additional utility in other areas of surgery where thermal treatment of maintenance of tissues is required with or without the capability of drainage. For example, an extended length catheter may be used for thermal treatment within the intestinal tract or the esophagus. Shorter versions may find utility in other areas such as nasal passages, otic areas, joints, i.e. arthroscopy, or the like, where adjacent tissues may be undergoing cryogenic or other thermal treatment. Indeed, varied forms of the apparatus and method may be used in virtually any body cavity where tissues are exposed to thermal extremes and damage to adjacent tissues is to be avoided. They may find particular utility anywhere cryogenic probe devices are being used to destroy and/or remove tumerous growths. 
   The molded embodiment of  FIGS. 1-6  has fewer parts than the block embodiment of  FIGS. 7-11  and therefore has manufacturing advantages. Molding rather than using machined and standard off the shelf components results in cost advantages. The block embodiment of  FIGS. 7-11  has the advantage of obviating up front tooling expenses. 
   The reservoir used is preferably a removable and disposable plastic container, such as an intravenous bag or a rigid container, which may be prepackaged with a fixed volume of sterile fluid, for example one liter. Clearly, just as larger or smaller catheters may be used in different situations, such larger and smaller catheters will require larger or smaller volumes of fluid. Appropriate fluids include sterile water, physiological saline, and the like and should be such fluids as are biocompatible and physiologically benign in the event of inadvertent rupture of the balloons. To allow for removal and return of the fluid in the closed system, the reservoir includes two fittings for connection of the inflow housing inlet section and outflow housing outlet section. These fittings may be standard piercable IV bag fittings. 
   A heating block is configured to removably accept and hold reservoir so as to heat the fluid contained therein. Preferably the heating block includes a vertical slot or window, which permits volume indicia on the reservoir to be viewed. The heating block itself may be a simple resistance heating means or an infrared heater or any other suitable heater capable of raising the temperature of the fluid within reservoir to approximately 42 degrees C. Heating the circulation fluid to this level has been found to provide sufficient warmth within the balloons to counter the cold of a cryoprobe and maintain the urethral tissues at about normal body temperature during cryogenic surgery of the prostate. Suitable heater control means allows the operator to select the desired temperature for heater block. 
   Downstream from the heating block is a pump, which provides motive force to the fluid to maintain a constant and even flow through the system. Once the desired flow rate and temperature are set, automatic control means are activated to maintain these levels. The automatic controls include monitoring sensors for supply temperature, return temperature and flow rate. In addition to the sensors and control means, pump and heater activating switches are included and electrically linked through a control circuit to their respective units as is a low flow alarm. 
   Thus, while the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the invention. Other embodiments and configurations may be devised without departing from the spirit of the invention and the scope of the appended claims.