Abstract:
A system and method for controlling the inflation, ablation, and deflation of a balloon catheter is provided. The system includes a balloon catheter, a console having a pressurized gas or liquid inflation source, and an umbilical system to deliver pressurized coolant to the balloon catheter. The system comprises a PID (Proportional Integral Derivative) controller or other pressure-sensing device that monitors the amount of pressure and volume within the balloon catheter. During inflation, the pressure and/or volume of fluid within the balloon is maintained at a target amount in order to provide sufficient mechanized pressure against the desired target region. The system limits the inflation pressure such that a safe quantity of gas would be released should a leak occur. If the amount falls below a certain threshold level, gas or fluid egress is presumed and the inflation process is halted.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     n/a 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     n/a 
     FIELD OF THE INVENTION 
     The present invention relates to a method and system for inflating and deflating balloon catheters and more specifically to a method and system for controlling the inflation and deflation of balloon catheters in order to safely and effectively ablate a tissue region. 
     BACKGROUND OF THE INVENTION 
     The use of fluids with low operating temperatures, or cryogens, has begun to be explored in the medical and surgical field. Of particular interest are the potential use of catheter based devices, which employ the flow of cryogenic working fluids therein, to selectively freeze, or “cold-treat”, targeted tissues within the body. Catheter based devices are desirable for various medical and surgical applications in that they are relatively non-invasive and allow for precise treatment of localized discrete tissues that are otherwise inaccessible. Catheters may be easily inserted and navigated through the blood vessels and arteries, allowing non-invasive access to areas of the body with relatively little trauma. 
     Catheter-based ablation systems are well known in the art. A cryogenic device uses the energy transfer derived from thermodynamic changes occurring in the flow of a cryogen therethrough to create a net transfer of heat flow from the target tissue to the device, typically achieved by cooling a portion of the device to very low temperature through conductive and convective heat transfer between the cryogen and target tissue. The quality and magnitude of heat transfer is regulated by the device configuration and control of the cryogen flow regime within the device. 
     A cryogenic device uses the energy transfer derived from thermodynamic changes occurring in the flow of a refrigerant through the device. This energy transfer is then utilized to create a net transfer of heat flow from the target tissue to the device, typically achieved by cooling a portion of the device to very low temperature through conductive and convective heat transfer between the refrigerant and target tissue. The quality and magnitude of heat transfer is regulated by device configuration and control of the refrigerant flow regime within the device. 
     Structurally, cooling can be achieved through injection of high pressure refrigerant through an orifice. Upon injection from the orifice, the refrigerant undergoes two primary thermodynamic changes: (i) expanding to low pressure and temperature through positive Joule-Thomson throttling, and (ii) undergoing a phase change from liquid to vapor, thereby absorbing heat of vaporization. The resultant flow of low temperature refrigerant through the device acts to absorb heat from the target tissue and thereby cool the tissue to the desired temperature. 
     Once refrigerant is injected through an orifice, it may be expanded inside of a closed expansion chamber, which is positioned proximal to the target tissue. Devices with an expandable membrane, such as a balloon, are employed as expansion chambers. In such a device, refrigerant is supplied through a catheter tube into an expandable balloon coupled to such catheter, wherein the refrigerant acts to both: (i) expand the balloon near the target tissue for the purpose of positioning the balloon, and (ii) cool the target tissue proximal to the balloon to cold-treat adjacent tissue. 
     One of the principal drawbacks to such a technique is that during the inflation phase coolant may seep out of the balloon and get into the bloodstream to cause significant harm. Therefore, if the balloon develops a crack, leak, rupture, or other critical structural integrity failure, coolant may quickly flow out of the catheter. Another situation that may occur during the balloon deflation phase is that the balloon may adhere to the ablated tissue causing severe damage. This may occur after cryoablation or cryomapping. Cryomapping is a procedure that chills conducting target tissue to create a transient electrical effect. By temporarily chilling the target tissue, it allows for precise site confirmation in order to prevent inadvertent ablation. During cryomapping, a procedure known as cryoadhesion takes place. Cryoadhesion is a procedure that ensures the catheter tip remains at the target cite for a seamless transition to cryoablation. In a cryoadhesion procedure, the tip of the catheter firmly attaches to the tissue when it freezes thereby reducing the risk of accidental slippage of the catheter tip. Therefore, during unmonitored balloon deflation, i.e. if the balloon deflates too quickly, the balloon, adhering to the tissue walls, may cause severe damage. 
     Accordingly, it would be desirable to provide an apparatus and method of monitoring and controlling the inflation and deflation phases of a balloon catheter that is adaptable and compatible with all types of balloon ablation catheters, and with all types of ablation procedures, for example RF ablation or cryoablation. 
     SUMMARY OF THE INVENTION 
     The present invention advantageously provides a method and system for controllably inflating and deflating a balloon catheter. The method and system allows for the monitoring of the inflation and deflation phases of a catheter system in order to allow ablation to take place, while detecting unwanted leaks of refrigerant into the bloodstream. Balloon leaks are identified, safety evacuation routes are provided, and a controlled deflation mechanism is presented that prevents damage to the interior blood vessel and tissue region, which may occur during unmonitored deflation due to the adherence of the expandable membrane to the interior of the vessel. 
     In its preferred embodiment, a method of inflating and deflating a catheter during an ablation process, the catheter having an expandable membrane, is provided. The method comprises the steps of controllably inflating the expandable membrane to a target pressure or volume, ablating a desired tissue region while maintaining the target pressure or volume of the expandable membrane, and controllably deflating the expandable membrane so as not to damage desired tissue region. 
     In another aspect of the invention, a method for inflating and deflating a catheter having an expandable membrane during an ablation process is provided. The catheter is part of a catheter system including a console, the catheter, and an umbilical system coupling the console to the catheter. The method comprises the steps of evacuating air from the expandable membrane by creating a vacuum in the expandable membrane, controllably inflating the expandable membrane proximate a desired tissue region, wherein the expandable membrane is inflated to a target pressure or volume in order to provide sufficient mechanical force against the desired tissue region, ablating the desired tissue region while maintaining the expandable membrane at the target pressure or volume, and controllably deflating the expandable membrane such that the desired tissue region is not damaged. 
     In still another aspect of the invention, an apparatus for inflating and deflating a catheter having an expandable membrane is provided. The apparatus comprises a console, the console including means for controlling the inflation and deflation of the expandable membrane and for determining if the expandable membrane maintains a target pressure or volume. The console also includes a pressurized inflation source. The apparatus further includes a catheter, and an umbilical system coupling the console to the expandable membrane and delivering pressurized media to the expandable membrane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1A  illustrates a first embodiment of a double balloon catheter used in conjunction with the present invention; 
         FIG. 1B  illustrates a catheter system used in conjunction with the present invention; 
         FIG. 1C  illustrates the double balloon catheter of  FIG. 1A  including a flow sensor located in the handle of the catheter; 
         FIG. 1D  illustrates the double balloon catheter of  FIG. 1A  including a pressure sensor located in the handle of the catheter; 
         FIGS. 2A-2E  illustrate a cryoablation system incorporating various embodiments of the apparatus and method of the present invention; 
         FIG. 3  is a schematic representing the mechanical components of the control console of the present invention; 
         FIG. 4  is a schematic representing the mechanical components of the inflation circuit portion of the control console of the present invention; 
         FIG. 5  is a schematic representing the mechanical components of the deflation circuit and main vacuum path of the control console of the present invention; and 
         FIG. 6  is a schematic representing the mechanical components of the safety vacuum path of the control console of the present invention; 
         FIG. 7  is a schematic representation of the embodiment illustrated in  FIG. 2A ; 
         FIG. 8  is a schematic representation of the embodiment illustrated in  FIG. 2B ; 
         FIG. 9  is a schematic representation of the embodiment illustrated in  FIG. 2C ; 
         FIG. 10  is a schematic representation of the embodiment illustrated in  FIG. 2D ; and 
         FIG. 11  is a schematic representation of the embodiment illustrated in  FIG. 2E . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is an apparatus and method for controlling the inflation and deflation of balloon catheters. In its preferred embodiment, the invention requires four steps to properly control the inflation and deflation of the balloon catheter. However, the invention allows for a variety of different implementations in order to accomplish this task. An intermediary control station containing a shut off valve and/or a coolant source may be implemented to assist in properly monitoring, controlling and maintaining the target balloon pressure and/or volume. 
     Referring now to the drawing figures in which like reference designations refer to like elements, a first embodiment of a double balloon catheter used in conjunction with the present invention is shown in  FIG. 1A . The catheter  1  includes a handle  2  having a number of proximal connector ports  3   a - 3   d . Port  3   a  may be a first vacuum connector, having a first vacuum lumen therein, such as a 10 French lumen. Port  3   b  may be a coaxial connector having both a vacuum lumen and injection therein, the vacuum lumen being a second vacuum lumen, such as a 8 French lumen. Port  3   c  may be an electrical connector. Port  3   d  may be a guidewire luer hub. 
     The handle  2  further includes a blood detection board  4  and pressure relief valve  5 . The distal end portion of the catheter  1  includes two balloons: an inner balloon  6   a  and an outer balloon  6   b  surrounding inner balloon  6   a . A soft distal tip  7  is located just distal to the two balloons  6   a  and  6   b . When refrigerant is injected into the balloons along lines R as shown, vacuum applied through the ports  3   a  and  3   b  will serve to draw any fluid within balloons  6   a  and  6   b  along arrows V out of the balloons and the catheter. Radiopaque marker bands M are located proximate the exit point of the refrigerant injected into balloon  6   a  to aid in the positioning and tracking of the device. 
     Catheter  1  includes an elongate shaft having a guidewire  8  and an inner shaft  9   a  and outer shaft  9   b . Exemplary embodiments of the inner shaft  9   a  include an 8 French shaft, while exemplary embodiments of the outer shaft  9   b  include a 10 French shaft. 
     A typical catheter system  10  is shown in  FIG. 1B . The system includes a console  20  coupled to one end of an umbilical system  12 . The opposing end of umbilical system  12  is coupled to an energy treatment device  22 . Energy treatment device  22  may be a medical probe, a catheter, a balloon-catheter, as well as other devices commonly known in the art that are smooth enough to pass easily through blood vessels and heart valves. As shown in  FIG. 1A , the energy treatment device  22  includes a balloon structure  23  that can be a single wall or a double wall configuration, wherein the double wall configuration places the space between balloon walls in communication with a vacuum source. 
     Umbilical system  12  is comprised of three separate umbilicals: a coaxial cable umbilical  14 , an electrical umbilical  16  and a vacuum umbilical  18 . An outer vacuum umbilical is used in the case of a double balloon system; it is not necessary for a single balloon system having only one vacuum lumen. If the user wishes to perform an RF ablation procedure, radiofrequency energy can be provided to electrodes on device  22  via electrical umbilical  16  to perform an RF ablation technique as is common in the art. Electrical umbilical  16  can include an ECG box  82  to facilitate a connection from electrodes on catheter  22  (not shown) to an ECG monitor. Coaxial umbilical  14  includes both a cooling injection umbilical and a vacuum umbilical that provide respective inlet and return paths for a refrigerant or coolant used to cool a tissue-treating end of device  22 . The vacuum umbilical  18  is used as safety conduit to allow excess coolant or gas to escape from device  22  if the pressure within the balloon on device  22  exceeds a predefined limit. The vacuum umbilical  18  can also be used to capture air through a leak of the outer vacuum system where it is outside the patient and as a lumen to ingress blood when in the patient. 
     Referring once again to  FIG. 1B , catheter system  10  may include one or more sensors #, which are used to monitor the amount of fluid or gas refrigerant injected through the umbilical system and into the balloons. It is contemplated that the sensors may be located in one of several locations throughout catheter system  10 . For example, sensor  11  may be located in console  20 , ECG Box  82 , and/or handle  2 . 
     Two different types of sensors are contemplated for use with the present invention in order to monitor how much coolant is flowing into the balloons. A flow sensor  13  shown in  FIG. 1C , measures the rate or speed of fluid or gas at a certain location. An exemplary embodiment of flow sensor  13  is the Microbridge Mass Air Flow Sensor by Honeywell®. 
     Alternately, one or more sensors  11  may be a pressure sensor  15  as shown in  FIG. 1D . Pressure sensor  15  in  FIG. 1D  is a differential pressure sensor that can determine the amount of pressure in the balloons by determining the difference in pressure between points P 1  and P 2  and the velocity through the restriction point d. An exemplary embodiment of pressure sensor  15  is the 26PC SMT Pressure Sensor by Honeywell®. 
       FIGS. 2A-2E  illustrate different embodiments of the catheter system  10  of the present invention. In general, the inflation/deflation system described herein can be used with both single and double balloon systems. For a single balloon system, the refrigerant is sprayed into the balloon and creates a circumferential region of cooling through the balloon&#39;s perimeter. The refrigerant expands and the vapor is drawn back into the console via the return vacuum lumen. With respect to a double balloon system, a second balloon and second vacuum lumen envelop the single balloon system and are always maintained under vacuum for safety reasons. The vacuum of the outer balloon will capture refrigerant escaping through any breach of the inner balloon system. A flow switch mounted on the outer vacuum system is used to monitor any flow activity. Under normal operation, no fluid should pass through the outer vacuum system. Any discussion of a “flow switch” herein implies a double balloon system. Otherwise, all inflation/deflation methods also apply to a single balloon catheter. 
     Each embodiment includes a console  20  or console  21 , an umbilical system comprised of varying combinations of separate umbilicals, and an ablation device  22 . Each of the embodiments shown in  FIGS. 2A-2E  is represented by more detailed corresponding schematics in  FIGS. 7-11 , respectively, and are discussed in greater detail below. 
       FIG. 2A  represents a typical catheter ablation system  10 . Console  20  is coupled to a catheter  22  via an umbilical system  12 , comprised of coaxial umbilical  14 , which transfers coolant from console  20  to catheter  22  and provides a return conduit for the coolant, electrical umbilical  16 , which transfers RF energy from console  20  to catheter  22  during an RF ablation procedure or electrical signals during a cryoablation procedure, and safety vacuum umbilical  18 , to allow for quick evacuation of coolant if needed. 
     Coolant is provided by a coolant source within console  20 . Coolant, typically N 2 O, passes through the internal piping of console  20  before being transferred to catheter  22  via the coaxial umbilical  14 . At the distal end of the umbilical, inside catheter  22 , the coolant is released inside the catheter tip cavity, which is under vacuum. Both the phase change from liquid to gas and the sudden expansion of the coolant are endothermic reactions, causing a temperature differential which results in the catheter tip or balloon freezing. The coolant vapor is then returned through the vacuum path via umbilical  14  and into console  20 , where it is evacuated through a scavenging line. 
       FIG. 2B  represents another catheter ablation system. However, in this embodiment, an intermediary station  74  is inserted into the catheter system. As explained in greater detail below, station  74  contains detection valves to detect a drop in balloon pressure which might indicate a leak, and shut off valves to terminate balloon inflation if necessary. Station  74  is coupled to console  21  and catheter  22  via electrical umbilical  16  and coaxial umbilical  14 . Vaccuum umbilical  18  provides an emergency evacuation path for coolant from the catheter. 
       FIG. 2C  represents the catheter ablation system of  FIG. 2A  including a secondary coolant source  78  used to re-inflate the expandable membrane, or balloon  23  of catheter  22  via syringe  76 . 
       FIG. 2D  illustrates two possible configurations for the ablation system. In a first configuration, a secondary coolant source includes a small tank or canister  80  located within an intermediary station  74 . In a second configuration, the secondary coolant source includes a small tank or canister  60  located inside the console  21 . In both configurations, the secondary coolant source is independent from the source of cooling provided by other components within the console  21  (the primary coolant source), and it does not require the same type of refrigerant that is provided by the primary coolant source. 
       FIG. 2E  illustrates a configuration where the secondary cooling source and the primary cooling source are unified and thus share the same source of refrigerant. 
       FIG. 3  refers to a schematic representing the console  20  portrayed in  FIGS. 2A and 2C . The schematic shown is designed specially for balloon catheters and contains a series of two and three-way solenoid valves and regulators that assist in monitoring the pressure of the balloon catheter  23 , which may drop quickly if a leak of fluid occurs. Device  22  (shown in  FIGS. 2A-2E ) is a catheter with an expandable membrane  23  at its distal end. Console  20  is represented by the schematic in  FIG. 3  that shows the layout of the internal mechanical components of console  20 . 
     In an exemplary embodiment, the system is operated in four phases. The first phase is the evacuation/flushing phase. When the catheter  22  is inserted inside the patient it is first necessary to evacuate air molecules from within the catheter, air contained inside the umbilical connecting the catheter  22  to the console  20 , as well as from the catheter shaft itself. Although it is not theoretically possible to evacuate 100% of the air molecules, by minimizing the amount of air within the umbilical and catheter shaft, the catheter is prepared for inflation and then ablation, while minimizing the dangers associated with fluid egress. 
     During the evacuation/flushing phase, a 3-way solenoid valve  24  is open toward vacuum pump  26 , which ensures that there is a vacuum in catheter  22 . The 3-way solenoid valve  24  can be replaced by a PID-driven proportional valve. In either configuration, the 2-way solenoid  28  that supports high pressure is closed to prevent any high-pressure gas from reservoir  30  from entering the inner vacuum system/balloon catheter during the refilling process. Reservoir  30  could be a tube or reservoir containing enough fluid volume to fill the umbilical tubes and catheter  22  to a predefined pressure. If the pressure within reservoir  30  exceeds a predetermined pressure setpoint, a check valve  32  will open to evacuate the exceeded amount of coolant such as, for example, nitrous oxide (N 2 O) in the system in order to keep a fixed amount of nitrous oxide in reservoir  30 . During this phase, reservoir  30  is filled with N 2 O received from N 2 O source  60 . The N 2 O is received from a high pressure line after leaves tank  60  and passes through a series of regulators, namely, a first regulator  34 , a second regulator  36  and then into either a third regulator  38  or a proportional valve, that are adjusted to the predetermined pressure. The reservoir pressure can be controlled through a pressure regulator  38  or through a proportional valve that would refill the tank with different pressure setpoints for different balloon sizes or different inflation pressures. The pressure setpoint can be programmed into a circuit, chip or other memory device that can be located in the handle. 
     Refilling valve  40  opens for a period of time and fills reservoir  30 . During this phase, the 2-way solenoid valve  28  remains closed. Also, during this phase, the system is under vacuum and provides verification for any leaks that occur. 
     Thus, when the catheter is outside the patient, any breach of the inner or outer vacuum systems will be detected by a high baseline flow through the console flow meter. In addition, a flow switch located in the console or in the catheter handle and mounted on the outer vacuum system will also detect a leak of air through a breach of the outer balloon or vacuum lumen. The flow switch is capable of detecting volumes of gas as little as 1 cc of vapor, and flow rates as little as 20 sccm. When the catheter is inserted into the patient, blood ingress through either the inner or outer vacuum lumens or both will be detected by the leak and blood detection systems. In the case of a constant pressure inflation with circulating flow, the balloon pressure can also be controlled with a PID-driven proportional valve located on the return vacuum lumen or a three-way solenoid valve in series with a pressure switch or pressure transducer. 
     Referring to  FIG. 4 , the inflation phase of the invention will now be discussed. Prior to positioning catheter  22  on the ablation site, the physician must first inflate the expandable membrane  23  inside the heart chamber and then position the balloon  23  proximate the ablation site. During this phase, the system is under vacuum and provides verification for leaks between balloon  23  and the blood. In one embodiment, balloon  23  is inflated by injecting fluid or gas through the umbilical under a fixed flow pressure. This insures a defined and constant pressure inside the balloon in order to provide a mechanical force for inflation. An alternate way to inflate balloon  23  is to use a fixed volume of inflation. This volume would be minimized in order to meet the constraints related to gas egress within the blood stream (maximum of 20 cc within 10 minutes) and meet the requirement for pressure needed to inflate the balloon under the harshest room conditions. 
       FIG. 3  illustrates the inflation portion of the console mechanics of  FIG. 2 . During the inflation phase, valve  24  is open toward reservoir  30  and valve  28  opens, while refilling valve  40  remains closed. A fixed amount of N 2 O is injected to inflate balloon  23  in order to provide sufficient mechanical force for inflation. If a leak occurs in the balloon, the released volume of N 2 O would be no more than 20 cc. The solenoid valve  44  (shown in  FIG. 33 ) remains open during this phase in order to ensure a vacuum in the safety line. If a leak occurs in the inner balloon of the catheter, the flow switch  42  ( FIG. 3 ), detects leaks as small as 1 cc of vapor. Flow switch  42  is active during all phases to prevent any leak of the inner balloon system in catheter  22 . The leak and blood detection systems are still active and monitoring any blood ingress through the outer vacuum lumen. After air has been flushed from catheter  22  and the umbilicals connecting catheter  22  to console  20 , and balloon  23  has been inflated, ablation may now take place. 
     A transition mode follows inflation but precedes ablation. In the case of cryogenic ablation systems, a transition method is needed to transition from closed pressurized volume to an open circuit, which allows the flow of refrigerant to enter and exit the catheter tip while at the same time controlling the balloon pressure in order to keep the balloon inflated and in place. During the transition, a pressure switch, which is adjusted to a pressure higher than atmospheric pressure but preferably lower than 20 psia, monitors the pressure inside the balloon catheter  22 . The solenoid valve  24  remains closed until the pressure in the catheter is higher than the preset switch value after which the solenoid valve opens to allow evacuation of excess refrigerant. When the pressure falls below the reset switch value, the solenoid valve  24  closes to keep the balloon inflated and above atmospheric pressure. During the transition, ablation is already initiated but the pressure switch controls the balloon pressure until refrigerant flow alone maintains the balloon open and above atmospheric pressure. The transition phase is considered complete when certain conditions are met: 1) when the pressure switch commands the solenoid valve  24  to open to vacuum and the balloon pressure remains above the present switch value; 2) the duration of the transition phase exceeds a predetermined time; and 3) the injection pressure reaches a predetermined value that is adequate to generate enough flow to maintain the balloon open. Check valve  56  is used to prevent any abnormal rise in the pressure in the catheter tip. Another check valve  58 , shown also in  FIG. 6 , prevents any excessive pressure in the safety vacuum line and in the event the solenoid valve  44  is blocked. 
     During the ablation phase, refrigerant is injected through the umbilical system into the ablation device  22 . When injection of refrigerant is desired, N 2 O gas is released from source  60  and provides high pressure liquid through a check valve  62  and a series of pressure regulators  34  and  36 . Regulators  34  and  36  are primary and secondary pressure regulators respectively, which serve to bring the gas pressure down to between 810 and approximately 840 psig. The liquid nitrous oxide goes through a proportional valve  64  driven by a Proportional Integral Derivative (PID) controller  66  so that the refrigerant pressure can be varied from 0 psig to approximately 760 psig, and through an injection solenoid valve  68  which remains open. The N 2 O then passes through a sub-cooler  70  with various refrigeration components such as a compressor, a condenser, a capillary tube and a heat exchanger, which insures its liquid state through the umbilical and into the small diameter catheter injection tubing. During injection, solenoid vent valve  46  is closed. To detect a failure of this valve, the pressure switch  72  will close when detecting a pressure higher than 15 psig, creating a failure signal. 
     During the injection phase, proportional valve  64  is used to vary the pressure inside the injection line. This in turn will vary the flow rate of refrigerant to the catheter tip. An increase in the flow rate (less restriction by the regulator) lowers the temperature of the catheter tip. Conversely, decreasing the flow rate allows the catheter tip to be warmed by its surroundings. 
       FIG. 5  illustrates the deflation and main path circuitry of the present invention. At the end of the ablation phase, the system provides a method to insure a controlled/slow deflation in order to prevent damaging the ablated tissue during balloon deflation. This can be a hazard due to cryoadhesion, which may occur when the catheter attaches to the tissue during freezing. Referring to both  FIGS. 3 and 5 , during deflation, the solenoid valve  24  ( FIG. 3 ) remains closed until the temperature in the balloon is higher than a predetermined temperature (usually above freezing to ensure that surrounding tissue has thawed). When the temperature increases to greater than the predetermined temperature, the solenoid valve  24  opens to vacuum and collapses the balloon. On both vacuum paths, liquid sensors and insulated liquid separators  48  and  50  ( FIG. 3 ) are installed to prevent any liquid from entering the vacuum pump  26 . If this occurs, injection and/or inflation will be stopped and both valves  52  ( FIG. 3) and 44  ( FIG. 3 ) will switch to atmosphere. 
       FIG. 6  illustrates the safety vacuum portion of the console circuitry of  FIG. 3 . If a leak occurs in the catheter during inflation or ablation, flow switch  42  can detect such a leak in amounts as small as 1 cc of vapor. Upon detection of the leak, inflation of the balloon catheter is stopped. Prior to inflation, the flow switch can detect leaks of the outer balloon or guide wire lumen when the catheter is in the air. In case of pressurization of the safety vacuum line ⅓ psi above atmospheric, a pressure relief valve  58  located distal to the flow switch will vent excess pressure. 
     Referring now to  FIG. 7 , one embodiment of the present invention is shown. The schematic in  FIG. 7  illustrates the mechanical connection of the console  20 , umbilical system  12  and catheter  22 . The representation in  FIG. 7  corresponds to the embodiment shown in  FIG. 2A . The internal components of console  20  are similar and correspond to those shown in greater detail in  FIG. 3  explained above. In this embodiment, the balloon  23  is inflated by receiving gas or fluid from source  60  via coaxial umbilical  14 . PID controller  66  controls the flow of pressurized fluid/gas from console  20  through umbilical system  12  to balloon  23 . 
       FIG. 8  shows an alternate embodiment of the invention in which an intermediary station  74  containing all components and circuits to operate the balloon catheter is coupled to console  10 , between the console and balloon catheter  23 . Station  74  includes a series of shut-off valves and detection switches. Detection circuitry within station  74  can detect if the volume of gas within balloon catheter  23  has exceeded a certain predetermined amount (i.e. 20 cc within the catheter and the umbilical system), and shut-off valves within station  74  are activated, preventing any further inflation. Station  74  advantageously provides a quicker and more effective way of detecting leakage of gas or liquid into the blood stream. If the pressure within balloon catheter  23  drops, this could be an indication that fluid within the balloon has escaped. By inserting station  74  within system  10 , a quicker and more efficient way of detecting leaks and preventing unwanted balloon inflation is provided. 
       FIG. 9  shows yet another embodiment of the invention. Here, balloon inflation can be performed by a syringe  76  coupled to a saline water source  78  or any other fluid media including gasses or liquids. This embodiment becomes practical when manual balloon inflation is required. 
     In  FIG. 10 , intermediary station  74  includes a second inflation source  80 . As in the embodiment depicted in  FIG. 8 , leak detection circuitry and shut-off valves located in station  74  provide an efficient way of detecting leaks and quickly prohibiting the further inflation of balloon catheter  23 . Should further inflation be required, a separate pressurized N 2 O source  80  is provided in station  74 , which is at a closer and more convenient location, i.e. nearer the catheter and not in a remote location such as console  20 . 
     In  FIG. 10 , the refilling source  80  is located in the intermediate box  74  and inflation occurs through the outer vacuum umbilical. In  FIG. 11 , the refilling source is the coolant tank  60  located in the cryoablation console and inflation occurs through the inner vacuum umbilical. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.