referring to fig1 an apparatus and method for cryo - surgical ablation of barrett &# 39 ; s esophagus has an endoscope 10 inserted into the esophagus e , of a patient p , adjacent to the stomach s . barrett &# 39 ; s tissue b lines the esophagus e above the lower esophageal sphincter . a conventional therapeutic endoscope 10 is illustrated in the drawings , although a smaller diagnostic endoscope is preferably used from the standpoint of patient comfort , particularly when a balloon shield is not being used . a specially designed endoscope can also be used . the distal end 12 of such an endoscope 10 is shown in fig2 showing an imaging camera lens 14 , illuminating light 16 , biopsy channel ( bore or lumen ) 18 with the catheter 20 therein , and an additional lumen 22 . the image picked up at the lens 14 is transferred via fiber optics to a monitoring camera 25 ( fig1 ) which sends tv signals via a cable 26 to a conventional monitor 28 , where the procedure can be visualized . by virtue of this visualization , the surgeon is able to perform the cryosurgery in the esophagus . through the lumen 18 is disposed a catheter 20 , preferably a conventional teflon catheter size 7 fr of 2 - 3 mm outside diameter . the catheter 20 protrudes from the distal end 12 ( i . e ., the end first inserted into the esophagus ) of the endoscope 10 and extends to the proximal end 30 ( closest to the operator , outside the patient ) where a physician &# 39 ; s hand h 1 guides the catheter 20 . as seen in the monitor image 28 of fig1 the distal end 12 of the catheter 20 may be bent at an angle . the catheter 20 is coupled to a tube extending near the bottom of a dewar flask 32 filled with liquid nitrogen or other liquified gas lg . as used in the present specification , “ gas ” in the phrase “ liquified gas ” means any fluid which is physiologically acceptable and which has a sufficiently low boiling point to allow the cryotherapy of the present invention . for example , such boiling point is preferably below about − 150 ° c . the gas is preferably nitrogen , as it is readily available , or alternatively argon . the dewar flask 32 may be adapted from an ordinary commercial container such as a thermos bottle holding as little as a quart of liquid , which can readily be refilled from a larger container . liquid nitrogen is also easily and safely handled in foam - insulated containers ( e . g ., styrofoam cups ). however , the container 32 is preferably a medium - capacity stainless - steel dewar flask of several liters capacity . a larger container , able to provide liquid for numerous operations over several weeks time , may be used . for expediency the large container may be mounted on a cart . the dewar flask 32 is closed and the interior space is pressurized with a small air pump 34 , which may alternatively be mounted in the container lid or elsewhere . fig1 shows schematically that the proximal end of the catheter 20 is coupled to a tube 35 , preferably by a standard luer lock 37 , and the lower end of the tube 35 is immersed in liquid nitrogen lg while the interior is pressurized by a free - running pressure pump 34 through a tube 38 . a pressure gauge 40 is preferably provided , or alternatively a safety valve with a preset opening pressure ( not shown ). the pressure is selected so as to permit adequate spray from the distal end of the catheter 20 . the interior of the dewar flask 32 is vented through a vent tube 42 which is preferably opened and closed by a valve operated by the physician &# 39 ; s hand h 2 . fig1 shows the thumb obstructing the end of the vent tube 42 . when the vent is closed , pressure builds up in the dewar flask 32 and nitrogen is pumped through the tube 35 to catheter 20 . while the valve is shown as a simple thumb - valve in fig1 it will be understood that such a valve could be a mechanical valve or an electromechanical valve , preferably controlled by a trigger mechanism , or the like , as could be readily envisioned and constructed by those of ordinary skill in the art . in a preferred embodiment of this invention , an electrically operated solenoid valve is employed in delivering the liquified gas to the catheter . of course , the solenoid is specifically adapted to function properly at cryogenic temperatures . the vent tube 42 is left open until the physician has positioned the catheter near the barrett &# 39 ; s tissue , as guided by the hand h 1 and confirmed by viewing the monitor 28 . the physician then closes the vent 42 and liquid nitrogen is pushed into the proximal end of the catheter 20 at the luer lock 37 . as the liquid nitrogen moves through the catheter 20 , it starts to boil and cool gas rushes ahead to emerge from the distal end or catheter tip 46 . the amount of boiling in the catheter 20 depends on the mass and thermal capacity of the catheter . since the catheter is of small diameter and mass , the amount of boiling is not great . ( the catheter would preferably be “ french seven ”.) after the catheter is cooled to a low temperature , and becomes filled with liquid nitrogen , the liquid nitrogen reaches the distal end of the catheter 20 near the distal end of endoscope 12 and begins to spray out of the catheter onto the barrett &# 39 ; s tissue . it is to be noted that the present invention may be able to freeze the barrett &# 39 ; s tissue sufficiently without actual liquid nitrogen being sprayed from the catheter , and that a spray of liquid may not be needed if the very cold gas can accomplish the task of freezing the epithelium . freezing is apparent to the physician by the frozen tissue b acquiring a white color ( cryoburn ), due to surface frost ( visible on the monitor 28 in fig1 ); the white color indicates gastrointestinal mucosal freezing sufficient to destroy the diseased tissue . the physician manipulates the endoscope 10 , vent 42 , and / or catheter 20 to freeze all of the barrett &# 39 ; s tissue . once the operation is complete , the endoscope 10 with catheter are withdrawn . the invention also contemplates valving the nitrogen at the distal end of the catheter , immediately adjacent the barrett &# 39 ; s tissue . apparatus for such valving 53 , shown in fig3 and discussed below , allows for control of the liquid nitrogen flow . since there is no gross damage to the esophagus ( for example , there is no laceration ), there is no need to treat the frozen area . the columnar cells of the barrett &# 39 ; s tissue soon die , and the lining is sloughed off to be replaced by healthy squamous tissue . because the invention uses liquid spray via a catheter 20 rather than contact with a cold solid probe , there no risk of a cold apparatus sticking to the esophagus and tearing the tissue . the plastic material of the catheter , such as teflon , is in little danger of sticking to the tissue because of its low thermal conductivity and specific heat . furthermore , it is not designed to touch the tissue . using a catheter the cooling rate ( rate of heat removal ) is much higher than with a solid probe since the sprayed liquid evaporates directly on the tissue to be frozen , which absorbs the entire heat of vaporization . the rate of rewarming is also high , since the applied liquid boils away almost instantly . no cold liquid or solid remains in contact with the tissue , and the depth of freezing is minimal . since freezing is accomplished by boiling liquid nitrogen , large volumes of this gas are generated . this gas must be allowed to escape . the local pressure will be higher than atmospheric since the gas cannot easily flow out of the gastrointestinal tract ; nitrogen gas will tend to enter the stomach s , whose junction with the esophagus ( the esophageal sphincter ) is immediately adjacent to the barrett &# 39 ; s tissue freezing zone . the present invention provides for the gas to escape by several alternate methods . first , the stomach may be suctioned with a separate tube 41 . for example , a nasogastric tube 41 as seen in fig1 a , 1 b and 1 c , which preferably runs outside of and adjacent to the endoscope 10 . suction may be provided by a suction pump 45 or other conventional means for suction . second , an escape path may be provided by an additional lumen in the endoscope . additional lumens are provided on so - called “ therapeutic ” endoscopes . “ diagnostic ” endoscopes typically have only one lumen , which would be occupied by the liquid nitrogen - delivery catheter 10 when such an endoscope is used in the present invention . the use of a two - lumen “ therapeutic ” scope in the present invention provides an extra lumen for use as an escape path for gas venting . the application of suction to such a vent lumen is also preferably provided . the lower esophageal sphincter may be blocked with an inflatable balloon 43 ( fig1 a and 1 b ), or some other shield , to prevent nitrogen gas from inflating the stomach . the balloon 43 may be of the “ tts ” ( through the scope ) type , passing through an additional lumen on the endoscope as is shown in fig1 . alternatively , a balloon may be placed alongside the endoscope 10 , such as an achalasia balloon . a bulb 44 or some other means for inflating and deflating the balloon 43 , such as a hand pump , can be provided . this may optionally be used in conjunction with stomach suction . fig2 shows a catheter tip 46 fastened on the end of the catheter 20 and adapted to spray liquid nitrogen in a radial pattern through plural holes 47 between the surface and an interior space fed by the catheter 20 . the length of the tip 46 is preferably chosen so that the entire area of the barrett &# 39 ; s tissue is frozen at once without the need for manipulating the endoscope or catheter to freeze the barrett &# 39 ; s area in sequential increments . the tip 46 may be of rigid material such as metal or stiff plastic , preferably the latter . alternatively , the entire endoscope and / or catheter may be moved up or down the esophagus to ensure that the entire barrett &# 39 ; s area is sprayed . fig2 also shows the distal end 12 of the endoscope 10 including a camera lens 14 , illuminating light 16 , biopsy channel or lumen 18 with the catheter 20 therein , and an additional lumen 22 . the endoscope shown in fig2 is a conventional therapeutic endoscope . a diagnostic endoscope would lack extra lumen 22 . alternatively to fig2 the catheter 20 itself may include a plurality of radial holes 49 and an end plug 50 ( fig5 ) to force the nitrogen to flow out of the radial holes . the end plug 50 is controlled by a wire ( not shown ). the catheter tubing , even though of plastic , becomes much more rigid at very low temperatures and approximates the stiffness of the separate tip 46 . fig3 depicts a wire - controlled end valve embodiment in which a tip 52 interacts with a disc 53 proximally controlled by the physician via a wire 54 running through the inside of the catheter 10 . the liquid nitrogen hits disc 53 and becomes atomized into a radial spray . fig4 shows an end 56 of the catheter 20 cut at an angle to deflect the spray to one side . with reference to fig6 - 9 , a particularly elegant and preferred gas supply system 70 is described . in this system , a pressurized gas tank 72 is employed . a convenient size for the tank has been found to be a 5 . 5 liter tank , and of course larger ( e . g . 35 liter ) or smaller size tank or even a canister would be operative . the inventors have found a double walled insulated tank ( not shown ) to be convenient because with adequate insulation the very low temperature of the liquid nitrogen gas can be maintained over a long period of time . the inventors have found the optimum pressure for the liquified gas in the tank to be 22 psi . the inventors have found 22 psi to be operative but higher or lower pressures are also operative . tank 72 is equipped with a pressure building coil or tube 74 for maintaining pressure . this coil 74 consists of metal tubing running from inside the tank to outside the tank and returning back to inside the tank . the tube 74 in operation contains circulating liquid nitrogen . if the pressure in the tank 72 drops below acceptable levels , valve 75 to the tube 74 can be opened to circulate gas outside of tank 72 through the tube 74 . the nitrogen liquid in the tube outside the tank will be warmed and returned to the tank . this warmed nitrogen liquid will boost the head pressure in the tank 72 and allow for more rapid delivery of nitrogen liquid to the catheter . in the tube arrangement shown , the valve 75 is hand operated , however , the valve could be automatic and would start circulating liquid through the tube or a coil once the pressure drops to unacceptable levels in the tank and to stop circulating once the pressure returns to normal . with normal pressure maintained in the tank , liquified gas will be more rapidly expelled from the tank to the catheter . the force of gas expelled from the tank is a function of the temperature and pressure of the liquid nitrogen in the tank . because of the large temperature differential between the ambient temperature and the temperature of liquid nitrogen , only a short length of tubing 74 is required . the gas supply system 70 illustrated in fig6 - 8 has a tank 72 equipped with valves and gauges . the tank 72 is equipped with a head gas valve 77 for relieving head pressure and a liquid nitrogen valve 78 which is opened to allow liquid nitrogen to flow to the solenoid valve 80 and then to catheter 20 . there are safety relief valves 81 , 82 on the tank 72 which relieve at pressures greater than 22 and 35 psi , respectively . in addition , the tank is equipped with a head pressure gauge 83 and a liquid level gauge 84 . the improved cryosurgical gas delivery system 70 has improvements which allow the physician to more accurately and comfortably deliver the cryogenic gas to the patient . the improved system 70 has a foot - pedal operated solenoid valve switch 86 ( fig6 and 9 ). this foot - pedal operated solenoid valve switch 86 actuates solenoid 80 between the tank 72 and catheter 20 . the foot pedal 86 has the advantage of allowing the physician &# 39 ; s hand to be free during cryosurgery . note , for example , that the system with the dewar flask ( fig1 ) requires the physician &# 39 ; s thumb to close vent 42 to produce pressure in the dewar flask causing nitrogen gas to flow . the improved tank 72 heating coil or tube 74 and foot - pedal operated solenoid switch 86 allows for quick delivery of adequate amounts for cryogenic spray to treat barrett &# 39 ; s esophagus or other tissue requiring cryoablation . referring to fig6 - 8 and 10 , an elegant design feature of the improved system 70 is the ability of the system to force super - cooled nitrogen gas through the catheter 20 at low pressure . this feat is possible because the improved system has an auxiliary bleeder vent or bleeder 88 positioned between the liquid nitrogen gas supply tank 72 and the catheter 20 . the bleeder is positioned at a point in - line where the internal diameter of the system ( i . e ., catheter ) is significantly reduced . this bleeder vent is designed to eliminate the elevated pressure produced at the catheter caused by the reduced internal diameter of the catheter relative to the larger internal diameter of the tube supplying gas to the catheter ; and by the volatilization of the liquid nitrogen to gas phase nitrogen . this bleeder 88 reduces pressure in the catheter 20 and at catheter tip 46 by venting gas phase nitrogen out the bleeder vent 88 . with this venting of gas phase nitrogen , liquid phase nitrogen exits the catheter tip 46 as a mist or spray at a pressure of approximately 3 - 5 psi compared with the tank pressure of approximately 22 psi . improved embodiments of this invention do not require a bleeder vent . as an exemplary embodiment the vent may simply be a piece of tubing attached to the liquid nitrogen supply by a “ t ” connection . as the liquid nitrogen makes its way from the tank 72 to the proximal end of catheter 20 , the liquid is warmed and goes to gas phase . this phase change creates additional pressure throughout the length of the catheter , but is especially important at the solenoid / catheter junction , where the diameter of the supply tube relative to the catheter lumen decreases from approximately 0 . 5 inches to approximately 0 . 062 inches , respectively . note that , in order to force low pressure liquid / gas nitrogen through this narrow opening , either the pressure of the supplied nitrogen must decrease or the diameter of the catheter must increase . the inventors did not wish to employ a highly pressurized system , nor did they wish to enlarge the catheter diameter . accordingly , the auxiliary bleeder 88 allows the liquid phase nitrogen to pass through this reduced diameter catheter without requiring modification of tank pressure or catheter diameter . without a pressure bleeder vent , the pressure of gas leaving the catheter would be too high and have the potential for injuring the tissue of the gastrointestinal tract . the pressurized tank can be provided with a bleeder or bleed - off to assure that the pressure of the cryogenic spray discharged from the tip of the catheter does not inadvertently injure the patient . while a dewar flask ( fig1 ) is illustrated and was used in the experiments reported below , it should be understood that the liquified gas source can be of any type . for example , a pressurized tank or a reservoir , such that the liquified gas is piped into a connecting site on the procedure room wall . the main requirement being that the liquified gas supply be controllable by the physician . it is an important preferred feature of the present invention that the spray be conducted in such a manner as to allow constant visualization by the physician of the tissue treatment as it occurs . if the temperature of the lens at the proximal end of the endoscope drops precipitously at the start of the liquid nitrogen spray , the moist air of the esophageal environment or of the air of the catheter which has been blown out ahead of the nitrogen flow will condense on the lens , thereby obscuring the physician &# 39 ; s view of the operative site . this can be substantially avoided by means of the suction pump 45 which will immediately suck out the moist air which is present prior to the arrival of the liquid nitrogen spray or cold nitrogen gas . because of this pumping out of the moist air as the spray commences and the replacement with extremely dry nitrogen gas , substantial amounts of moisture will not form on the lens 14 during the procedure , allowing an excellent view of the operative site by the physician during the procedure . this condensation effect is augmented by the fact that the catheter itself is preferably not wrapped in additional insulation . this causes the temperature of the nitrogen gas exiting the catheter at the distal end to be relatively high at the beginning of the spraying operation and gradually cooling as the catheter cools . indeed , in the tests conducted in the esophagus of pigs discussed below in the examples , often 10 - 20 seconds were necessary before significant freezing was seen through the endoscope . if the catheter is substantially insulated , the interior of the catheter will cool much more quickly as it will not be picking up heat from the outside . with this insulated catheter , it is to be expected that the liquid nitrogen would be sprayed onto the tissue almost immediately , causing much faster freezing and , thus , allowing less control on the part of the physician . another reason that the lens does not fog or frost in the present invention is that the esophagus is flushed out with nitrogen gas , which is extremely dry . the nitrogen gas is moisture free because the liquid nitrogen is condensed out of atmospheric gases at a temperature − 197 ° c . colder than the temperature at which moisture is condensed out . the combination of relatively warm , and completely dry nitrogen gas , together with suction flushes all moist air from the esophagus . as the temperature of the gas entering the esophagus falls , so does the surface temperature of the camera lens 14 . ordinarily at that time the lens 14 would be cold enough to condense moisture and fog , however , since the esophagus is dried out ( in contrast to its usual highly moist state ) there is no moisture to condense . thus , the lens 14 stays un - fogged and un - frosted and continues to provide a clear view of the operation . on the other hand , if the esophagus is not vented with suction and / or the esophagus is not preliminarily flushed with dry nitrogen gas ( perhaps because the catheter is insulated , lowering its heat capacity , and / or the nitrogen delivery pressure is too high ), then the lens is likely to fog or frost and the physician cannot operate effectively . in order to deal with the moist air problem , there is supplied in the preferred embodiment of this invention a nasogastric tube 41 ( fig1 and 1 a - 1 c ). during the cryosurgical procedure the nasogastric tube is inserted prior to inserting the endoscope 10 and catheter 20 . the nasogastric tube 41 , when connected to a pump 45 , can serve to evacuate moist air from the esophagus prior to cryosurgery . with moist air removed , the t . v . camera lens 14 is not obscured by fog and the physician can perform cryosurgery with an unobstructed view . alternatively , if fogging occurs during cryosurgery , the nasogastric tube and pump can be used to evacuate the esophagus . in the most preferred embodiment , the composition of the catheter or the degree of insulating capacity thereof will be selected so as to allow the freezing of the mucosal tissue to be slow enough to allow the physician to observe the degree of freezing and to stop the spray as soon as the surface achieves the desired whiteness of color ( cryoburn ). the clear observation results from the removal of the moist air and sprayed nitrogen by the vacuum pump ; in combination with the period of flushing with relatively warm nitrogen prior to application of the spray of liquid nitrogen which is caused by the relative lack of insulation of the catheter . preferably , the catheter has a degree of insulation which permits at least five seconds to pass from the time said means for controlling is opened to the time that liquified gas is sprayed onto the mucosa . with reference to fig6 and 12 , an electronic monitoring and recording system 90 is illustrated . the electronic components of the system 90 comprise a temperature sensor or probe 92 and timer 96 . also connected to the monitoring and recording system 90 are the foot - pedal 86 for actuating the solenoid 80 and recording console 95 . in fig6 an electric power cord 93 runs from solenoid 80 to control box 90 . the temperature sensor 92 is thin and can be inserted into the esophagus beside the catheter 20 . in a preferred embodiment , the temperature sensor 92 and catheter 20 can be inserted separately or as an integral unit of sensor and catheter combined , or alternatively the sensor can be inserted through an extra lumen of the endoscope to come in contact with the tissue of the esophagus . the temperature sensor 92 sends temperature readings to the electronic monitoring and recording system 90 for processing and recordation . the liquid gas flow is started by actuating solenoid foot - pedal 86 and ends with release of the solenoid foot pedal 86 . the electronic monitoring and recording system 90 records the times at which cryoburn starts and ends . temperature in the context of time will be recorded for the cryosurgery . this recordation allows for better data acquisition and documentation . there is an automatic cut - off if a time or temperature limitation is exceeded . in the event of a cut - off , the electronic monitoring and recording system can be reactivated by pushing the reset button 98 ( fig9 ). current time and temperature readings are presented in the windows 99 as led numbers . the windows in fig9 will indicate total time 100 ; shut - down time 101 ; cryotime 102 ; cryotime set 103 ; and temperature 104 . within the main console of the electronic monitoring and recording system 90 of fig9 is a printing unit 95 which prints and records 95 the time and temperature during the cryoburn . every event is recorded , e . g . time , on and off , temperature , etc . fig6 and 9 show alternative models of the electronic monitoring and recording system . the printed record 97 is shown in fig9 . the operating sequence of components used in carrying out applicant &# 39 ; s process are described in fig1 a and 12b . fig1 a describes the nitrogen source 72 , foot - actuated 86 solenoid valve 80 , electronic control box and printer 90 , endoscope 10 with catheter 20 and t . v . monitor 28 for treating a patient with barrett &# 39 ; s syndrome . in fig1 b is shown a completely automated system with sensors and a microprocessor for performing cryosurgery . the completely automated system of 12 b is similar to the system of 12 a except that various sensors for temperature , time , etc . 92 send an output signal ( s ) to a microprocessor controller 90 to control the shut - down of the system if pre - set limits are exceeded or if pre - set conditions are not met . the steps for performing the esophageal cryosurgical procedure are described in flow chart fig1 . the electronic circuitry for the electronic monitoring and recording system 90 is described in fig1 a and 14b . the components or paraphernalia required to practice the method of the present invention may be packaged and sold or otherwise provided to health - care providers in the form of a kit . the kit is preferably sealed in a sterile manner for opening at the site of the procedure . the kit will include the catheter , having the spray means at one end , as well as a means for connecting the catheter to the source of liquified gas . this means for connecting may be a simple luer connection on the opposite end of the catheter from the spray means . however , the term “ means for connecting said catheter to a source of liquified gas ” is intended to include any other device or apparatus which allows the catheter to be connected to the gas source . many of the components of the cryosurgical system are conventional medical appliances . for example , the endoscope is a conventional medical appliance and would not necessarily have to be supplied as part of a kit . one of the components to be supplied in a kit or sterilized package is a combined catheter - bleeder vent . with reference to fig1 a - 10f and 11 , this invention envisions the catheter 106 at its proximal end being integrally provided with a pressure reducing bleeder vent 107 as a single unit . the unit can be attached to the gas supply tube through a luer lock 37 connection and can be supplied to the user in a sterile package or kit 108 ( fig1 ). with reference to fig1 a - 10f , there is schematically represented tube connector 109 for connecting a tube running from the liquid nitrogen supply tank 72 , to solenoid 80 . the solenoid has a connector fitting to which can be attached a vented catheter . the vented catheter comprises as an integral unit a connector fitting 37 attached to the solenoid 80 along with a vent 107 between the connector 37 and the catheter 106 . the catheter and bleeder unit can be supplied with various modifications in the placement of the bleeder vent relative to the catheter . in addition , envisioned are a variety of reductions between the solenoid valve and the catheter . for example , fig1 a - 10c show that the actual position of the bleeder relative too the catheter is open to design options . fig1 a - 10f show a blunt reduction ( i . e ., reduction occurs just before the catheter ). fig1 d - 10f depict a tapered reduction ( i . e . the diameter is reduced gradually over the entire length ). another option would include stepping reductions . in addition , the inventors contemplate that the vent can have a piece of tubing attached to lead away gas and the placing of a strainer ( similar to a colander ) inside of the tubing from the solenoid to the catheter . this strainer would serve as a mechanical means for separating the liquid phase from the gas phase . note particularly that the solenoid valve is specially designed to accept cryogenic gases and is commercially available . referring to fig1 , the inventors envision supplying the catheter and vent unit 105 as a separate item . in this way , the unit can be supplied in a sterile packet or kit 108 to be used with existing equipment found in hospital operating rooms . the kit may contain a nasogastric tube 41 . the means for controlling the flow of liquified gas to the catheter is also preferably present in the kit and may be connected to or may be part of the means for connecting the catheter to the source of liquified gas . for example , the connector may contain a valve therein or the valve may be a separate element connected between the connector and the catheter or between the connector and the nitrogen source . the endoscope may either be part of the kit or an available conventional endoscope may be used in conjunction with the remaining components of the kit . the kit will also optionally contain the means for withdrawing gas , such as a tube and a means connectable to the tube for withdrawing gas from the tube . such means connectable to the tube for withdrawing gas may be a vacuum pump or any other device or apparatus which will accomplish the function of withdrawing gas from the tube . the vacuum pump is optionally omitted from the kit as a source of vacuum is often found in hospital rooms in which such a procedure is to take place . the means for blocking the lumen is also optionally present within the kit . thus , for example , the kit may contain a balloon catheter or any other device or apparatus which can accomplish the function of blocking the lumen when in use . the term “ container ” or “ package ” when used with respect to the kit is intended to include a container in which the components of the kit are intended to be transported together in commerce . it is not intended to comprehend an entire procedure room in which the individual components may happen to be present , an entire vehicle , a laboratory cabinet , etc . the claimed “ means for causing fluid flowing therethrough to be sprayed in a radial direction ” is intended to comprehend the illustrated embodiments of catheter tips shown in fig2 - 5 , as well as any functional equivalents thereof . any device which can be connected to the end of a catheter which will direct fluid in the catheter to be sprayed substantially radially may be used . the terminology “ a radial direction substantially perpendicular to the axis of the catheter ” is intended to include a unidirectional spray over a small arc in the radial plane or an omnidirectional spray through 360 ° of the radial plane , or any arc therebetween . the term “ substantially perpendicular ” is not intended to limit direction of the spray to a plane at an angle of 90 ° to the axis of the catheter but to include any type of spray which will allow the mucosa of the lumen , such as the esophagus which is coaxial to the catheter to be sprayed , near the locus of the tip of the catheter and to exclude a spray which is only substantially axial . the claimed “ means for controlling the flow of liquified gas ” is intended to encompass the simple thumb - valve illustrated in fig1 as well as any other mechanical , mechano - electrical , etc ., device that will accomplish the function of controlling the flow of liquified gas from the source to the catheter . this includes any type of valve , including , for example , a trigger valve , a rotary valve , a stopcock , etc . the valve may be manually controlled , electrically driven , remotely controlled , etc . other means for controlling the flow of liquified gas are not excluded . the claimed “ means for withdrawing gas ” is intended to include the illustrated tube 41 and vacuum pump 45 , as well as any functional equivalent thereof . it does not matter whether the tube withdrawing the gas passes through the endoscope , around the endoscope , or even is placed into the area from which gas is to be withdrawn by incision . the only important function is the withdrawal of the gas from the area in question . while a vacuum pump is preferred , any other type of pump or device which will cause the withdrawal of the gas is intended to be encompassed by this terminology . other means for withdrawing gas are not excluded . the claimed “ means for blocking the lumen ” is intended to encompass not only the balloon catheter 43 and the shield of fig3 but also any other device or technique which will accomplish the function of blocking the lumen , e . g ., the esophagus when the condition being treated is barrett &# 39 ; s esophagus . any manner of substantially preventing the gas being sprayed through the catheter from passing beyond the point of blockage is intended to be included by this terminology , including , for example , physically squeezing the lumen from the outside or chemically causing the lower esophageal sphincter to close , etc . the claimed “ means for forcing said liquified gas ” is intended to include not only the illustrated pressure pump 34 but any other device or apparatus which will force the liquified gas from its source to the catheter . this includes use of a pre - pressurized container of liquified gas or apparatus which causes gas to liquify and then be directly directed to the catheter , etc . no manner of driving the liquified gas from the source to the catheter is intended to be excluded . each of the steps set forth in the method claims herein are likewise intended to comprehend not only the specific acts described in the specification but any other acts which will accomplish the function set forth in the method step . thus , for example , the step of adjusting the catheter may be accomplished by hand , as illustrated in fig1 or by any other technique up to and including use of a complicated remote controlled robotic adjusting apparatus . the same is true for all of the other method steps for performing specified functions . the inventors have concluded from preliminary test results that a 30 second “ cryoburn ” time was adequate to ensure the appropriate tissue destruction , and thus appropriate cellular healing of damaged tissue ( this conclusion was based on a 30 day follow up period ). “ cryoburn ” is a term defined by the instance that the normally “ pinkish ” esophageal tissue turns white ( much like freezer burn ). a range for the “ cryoburn ” time could be 5 - 10 seconds to 2 minutes or more depending on the substrate to be treated . due to the nature of the system , “ cryoburn ” does not immediately occur , but rather requires that the entire fitting and catheter system become cool . typically this required approximately 20 - 30 seconds from the time that the solenoid foot pedal is depressed , and liquid nitrogen is allowed to flow from the tank . during animal testing the approximate temperature that cryoburn was first observed was at approximately − 10 degrees c . the temperature range for cryoburn would be approximately − 10 to − 90 degrees c . in carrying out the procedure , a nasogastric tube is first inserted into the esophagus , after which an endoscope is inserted . the endoscope is supplied with light and fiber optic t . v . camera . optionally , attached to the endoscope will be a temperature probe to sense the temperature and report the temperature to the recording console . once the nasogastric tube , endoscope and temperature probe are in place , the catheter attached to the gas supply will be inserted into a lumen of the endoscope . before liquid gas is supplied , the esophagus is ventilated using the nasogastric tube to remove moist air from the esophagus ( if required ). with the moisture evacuated and the endoscope is properly positioned , gas can be supplied to the catheter by actuating the solenoid with foot pedal . once the solenoid is actuated gaseous nitrogen and then a spray of liquid nitrogen will come from the tip of the catheter . the cryoburn will generally last for 30 seconds to 2 minutes . the cryospray device of fig1 was used in experiments to assess the efficacy and safety of this device in mucosal ablation in me distal esophagus of swine . the catheter 20 was a long 7 fr ercp - like catheter placed through the biopsy channel of an olympus gif - 100 endoscope . the swine were sedated using telazol and xylazine given intravenously . general anesthesia was not necessary . liquid nitrogen was sprayed on the distal 2 cm of the esophagus in 16 swine under direct endoscopic observation until a white “ cryo - bum ” appeared , usually within 10 - 20 seconds . duration and location of the spray were varied to assess histologic response and dept of “ cryo - bur ”. the swine were then re - endoscoped on days 2 , 7 , 14 , 21 and 30 to obtain biopsies from the injury site , assess mucosal ablation and re - epithelialization . all swine were then euthanized and underwent necropsy . freezing of the esophageal mucosa was recognizable by a white “ cryo - burn ” with sharply demarcated margins . this was followed by slow thawing within minutes and then mucosal erythema . sixteen swine underwent hemi - circumferential to circumferential cryotherapy of their distal esophagus varying the duration of “ cryo - burn ” from 10 - 60 seconds . blistering and sloughing of the superficial mucosa occurred within 2 to 7 days of the cryospray . mucosal damage occurred only at the cryo site . biopsies 48 hours after cryospray consistently demonstrated coagulative necrosis involving the mucosal layer and biopsies 30 days after cryospray consistently demonstrated complete re - epithelialization of the injured area . complications included one esophageal stricture and one esophageal perforation in experiments with prolonged cryo - burn . these experiments on living swine , which are a valid model of the human esophagus , establish that cryotherapy spray of liquid nitrogen via upper endoscopy is a simple technique capable of inducing controlled superficial mucosal damage with complete healing in the esophagus . the foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can , by applying current knowledge , readily modify and / or adapt for various applications such specific embodiments without undue experimentation and without departing from the generic concept , and , therefore , such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments . it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation . the means and materials for carrying out various disclosed functions may take a variety of alternative forms without departing from the invention . thus the expressions “ means to . . . ” and “ means for . . . ” as may be found in the specification above and / or in the claims below , followed by a functional statement , are intended to define and cover whatever structural , physical , chemical or electrical element or structure may now or in the future exist for carrying out the recited function , whether or not precisely equivalent to the embodiment or embodiments disclosed in the specification above ; and it is intended that such expressions be given their broadest interpretation . the inventors have continued to make improvements to their invention regarding use of low pressure , heated catheter , etc . lee in u . s . pat . no . 3 , 298 , 371 teaches a freezing probe to be used in neurosurgery . attached to this freezing probe is a heater . this heater is provided in the event the insulation on the exterior of the probe is inadequate to thermally isolate non - target tissue surrounding the probe . in this way , non - target areas will not be affected by the cold , and only the cold probe tip will be presented to the target area . thomas u . s . pat . no . 3 , 507 , 283 shows a cryosurgical probe which employs heating wires along the external surface of the instrument . also shown by thomas is a cover of heat shrinkable polytetrafluoroethylene to protect the user &# 39 ; s hand from the cold . chang in u . s . pat . no . 5 , 400 , 602 teaches various types of plastic materials used for cryotubing which remain flexible during use . griswold u . s . pat . no . 5 , 658 , 276 teaches a cryoprobe with a heated exterior so that areas of the body not being treated by the probe are not damaged by the cold instrument . the heat is produced by a battery - energized resistive wire wrapped around the external surface of the probe . u . s . pat . no . 5 , 800 , 488 to crockett teaches a cryoprobe wherein different methods are used to heat the external surface . the inventors have continued to make improvements to their invention . they have produced a heated catheter . the heated catheter in a preferred embodiment is a composite constructed of three different materials ; in three different layers . the catheter itself ( as the first layer ) is made of extruded polyimide . surrounding the first layer ( the catheter ) is a layer of magnetic wire wrapped around the outer diameter of the polyimide catheter . as a top or final layer , there is supplied a thin polyester heat shrink . more specifically , the heated catheter ( cryocatheter ) can be defined as an extruded polyimide tube ( o . d . 0 . 092 ″). over the catheter is wrapped a layer of magnetic copper wire ( 0 . 007 ″ diameter ). a number of different diameter wires are available . the inventors put together prototypes with 0 . 003 ″ diameter wire , 0 . 002 ″ diameter wire , 0 . 005 ″ diameter wire , etc . a 0 . 007 ″ diameter wire was the best for the desired voltage , but the invention does not exclude the use of wires of other diameters . the wrappings of wire that functioned the best were 8 wraps per inch ( a single strand was run the length of the catheter , and the wrapping was applied back over this single strand to complete the electrical loop . double strand wrapping with the wrap spacing ( up to 25 wraps per inch ) would be operative . a selected preferred voltage for application is 12 volts and 1 amp . voltages of 5 , 12 , 17 and 24 volts have been tested . the important thing to keep in mind is that different diameter wires work well if wrapped to the correct density and heated with the appropriate amount of voltages . the final layer employed is a thin ( 0 . 00025 ″) polyester heat shrink . this heat shrink serves to hold the wire in place and to seal the wire from patient contact . the hub , or connection of the catheter to the cryo - system , has been designed to incorporate the electrical contacts required by the heating system . the heated catheter provides a number of advantages over a traditional catheter : polyimide , the cryo - catheter material base , acts as a strong insulator and transports the liquid nitrogen with minimal thermal temperature loss resulting in a shorter time to achieve the clinically required cryoburn . the heating mechanism allows the catheter to be removed from the endoscope lumen immediately following the cryo - therapy . using a traditional catheter , the catheter is frozen into the endoscope lumen for 30 - 40 seconds following the therapy . this freezing to the endoscope lumen may result in damage to the endoscope . in an embodiment of the invention , the bleeder valve has been found to be unnecessary so long as low pressure can be maintained by other means . in the improved embodiment , a cryoburn is carried out without the need for a bleeder valve . in this new embodiment with the tank pressure at 45 psi and the catheter being a 9 french , the cryo - procedure took 4 minutes and 50 seconds . with a 10 french catheter using 45 psi , the cryo - procedure took 2 minutes and 50 seconds to achieve a cryoburn temperature . with the bleeder valve , it takes 10 - 20 seconds to achieve cryoburn . the ideal low pressures operative for this invention should be in the range of 3 - 45 psi . the most ideal pressure is determinable by those skilled in the art . it is clear from experiments performed that a bleeder valve is not absolutely essential to this invention since low pressure cryoablation can be carried out through low head pressure in the storage tank or through selection of the proper inner diameter of the catheter . based on experiments carried out with the bleeder valve embodiment a shorter time period is required for cryoburn . the new fittings on the device will be vacuum insulated . this will keep the fittings from frosting or feeling super cool to the human touch . in addition , the hub or connective fittings which couple the catheter to the cryosystem have been redesigned and improved to accommodate electrical contacts required for the heating system . the inventors have continued to make improvements to their cryogenic heated catheter . among the improvements contemplated by the inventors is the heating coil on the heated catheter being energized in “ series ” or that the catheter is heated with a continuous length energized from two ends . also contemplated is a catheter with the heating element in parallel . this will result in heating short segments ( 5 - 10 segments per catheter ) quickly and with more energy . the inventors may adjust the wrappings of the heating coil so that the loops touch one another . a parallel electrical transfer may be necessary . it may be feasible to employ flat wire ( square wire ) as opposed to round wire . whether to use series or parallel spacing will be determined based on individual use . the inventors contemplate coating the gap between the wires with a heat sink which will act to absorb radiated heat from the heating coil to dispense the heat to the outside of the catheter . also contemplated by the inventors is a spray coat or liquid paint of a nichrome conductor . in this embodiment the entire catheter could be energized quite quickly . the inventors envision alternate means for diverting freezing temperatures from non - target areas . examples of such diverting means is a polystyrene tape to function as an insulator . alternatively , the catheter may be made of polystyrene or some other insulating material . during the cryoburn the heat of the catheter remains active . this prevents the accidental injury to non - target tissue . obviously , many modifications may be made without departing from the basic spirit of the present invention . accordingly , it will be appreciated by those skilled in the art that within the scope of the appended claims , the invention may be practiced other than has been specifically described herein .
a method and apparatus to treat barrett &# 39 ; s tissue , a pre - cancerous condition , by removing the epithelium above the lower esophageal sphincter through cryo - ablation . an endoscope with fiber optics is used to view the operation , and a catheter for supplying liquid nitrogen is passed through the lumen of the endoscope . liquid nitrogen at low pressure is sprayed directly onto the barrett &# 39 ; s tissue through the catheter while the physician views the operation through the fiberoptics of the endoscope and controls the spray via a valve . freezing is indicated by whiteness and shows that the epithelium has been cryoablated . the apparatus can also be used to treat various other gastrointestinal tract lesions . the catheter is insulated to withstand extremely cold temperatures without becoming stiff and without affecting the inherent flexibility and maneuverability of the endoscope .