Abstract:
The disclosed medical device includes an inflatable structure configured for positioning in an airway of a human patient and a valve in fluid communication with the inflatable structure. The valve includes a member that is movable between an open position and a closed position. The valve prevents fluid from escaping the inflatable structure when the member is in the closed position. The valve permits fluid to escape the inflatable structure when the member is in the open position. The valve includes a resilient element. The resilient element provides a first force that biases the member towards the closed position. The valve includes a temperature sensitive element. The temperature sensitive element generates a second force that biases the member towards the open position. The first force is greater than the second force when the ambient temperature is below a first value. The first force is smaller than the second force when the ambient temperature is above a second value.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to inflatable medical devices. More specifically, the present invention relates to protecting medical devices during sterilization by providing automatic venting at high temperatures. 
     The laryngeal mask airway device is a well known device that is useful for establishing airways in unconscious patients. FIG. 1 shows a perspective view of a prior art laryngeal mask airway device  100 . Laryngeal mask airway devices such as device  100  are described for example in U.S. Pat. No. 4,509,514. Device  100  includes a hollow airway tube  110  and an inflatable mask portion  130 . Tube  110  extends from a proximate end  112  to a distal end  114  and defines an interior airway lumen that extends through the tube from the proximate end  112  to the distal end  114 . Mask portion  130  defines, at least when inflated, a central opening  136 . Mask portion  130  is coupled to the airway tube such that the lumen of the airway tube communicates with the mask portion&#39;s central opening and such that the device  100  provides a sealed internal passage that extends from the proximate end  112  to opening  136 . 
     In operation, the mask portion  130  is deflated, and then the mask portion is inserted through a patient&#39;s mouth into the patient&#39;s pharynx. The mask portion is preferably positioned so that a distal end  140  of mask portion  130  rests against the patient&#39;s normally closed esophagus and so that the opening  136  of the mask portion  130  is aligned with the entryway of the patient&#39;s trachea (i.e., the patient&#39;s glottic opening). After the mask portion is so positioned, the mask portion is inflated thereby forming a seal around the patient&#39;s glottic opening and this establishes a sealed airway extending from the proximate end  112  of the tube  110  to the patient&#39;s trachea. The proximate end  112 , which remains outside the patient, may be coupled to a ventilator for providing ventilation to the patient&#39;s lungs. 
     Referring again to FIG. 1, laryngeal mask airway device  100  also includes an inflation tube  138  for permitting selective inflation or deflation of mask portion  130 . An inflation valve  150  is connected to the proximate end of the inflation tube  138  and the distal end of inflation tube  138  is connected to the mask portion. The inflation valve  150  is normally closed so as to maintain the current pressure in mask portion  130 . However, valve  150  may be opened to permit inflation or deflation mask portion  130 . 
     FIG. 2A shows a sectional view of inflation valve  150 , when the valve is closed (or when fluid may not freely flow between a first end  152  of the valve and a second end  154  of the valve). FIG. 2B shows a sectional view of inflation valve  150 , when the valve is open (or when fluid may freely flow between first and second ends  152 ,  154 ). FIG. 2C shows a view of the first end  152  of valve  150  taken in the direction of arrow  2 C— 2 C as shown in FIG.  2 A. FIG. 2D shows an exploded sectional view of inflation valve  150 , in which, for convenience of illustration, the space between opposite sectional views of body  160  has been artificially enlarged. FIG. 2E shows a more detailed sectional view of a typical prior art inflation valve  150 , when the valve is closed. 
     As shown, inflation valve  150  includes a hollow body  160 , which defines a central channel  169  that extends entirely through the body from end  152  to end  154 . Valve  150  also includes a movable member, or pin,  170 , and a spring  180 , both of which are disposed within the central channel  169  of hollow body  160 . One end  182  of spring  180  contacts a shoulder  162  of body  160 . The other end  184  of spring  180  contacts a shoulder  172  of pin  170 . The spring biases pin  170  away from shoulder  162  (or upwards as shown in FIGS. 2A,  2 B, and  2 D) such that a shoulder  174  of pin  170  normally contacts a shoulder  164  of body  160 . 
     In the normal resting position of valve  150  (shown in FIG.  2 A), contact between shoulder  174  (of pin  170 ) and shoulder  164  (of body  160 ) forms a seal and effectively prevents fluid from passing through channel  169  between the first end  152  and the second end  154  of valve  150  thereby closing the valve. The position of pin  170  shown in FIG. 2A may be regarded as a “closed position”. As shown in FIG. 2B, valve  150  may be opened by biasing pin  170  such that shoulder  174  (of pin  170 ) is separated from shoulder  164  (of body  160 ). Valve  150  is “open” as soon as shoulders  174  and  164  separate from one another. Once valve  150  is open, fluid may pass through channel  169  between the first end  152  and the second end  154  of valve  150  (i.e., fluid may pass from the first end to the second end or from the second end to the first end depending upon relative pressures at the valve ends). Any position of pin  170  in which shoulder  174  (of pin  170 ) is separated from shoulder  164  (of body  160 ) may be regarded as an “open position”. If biasing of pin  170  continues, a shoulder  176  (of pin  170 ) eventually contacts a shoulder  166  (of body  160 ). Shoulder  166  serves to limit the motion of pin  170  such that once shoulders  176  and  166  contact one another, further movement of pin  170  (in a direction that continues to separate shoulders  174  and  164  from one another) is prevented. Unlike shoulders  174  and  164 , the shoulders  176  and  166  do not form sealing surfaces, such that valve  150  is open even when shoulders  176  and  166  are in contact. 
     In laryngeal mask airway devices, the second end  154  of valve  150  is normally connected to the inflation line  138  (shown in FIG.  1 ). The valve  150  is normally closed so that if the mask portion  130  is inflated or pressurized, valve  150  maintains the pressure in the mask portion, or prevents gas in mask portion  130  from passing through valve  150  and escaping to the atmosphere external to the device. In its normally closed position, valve  150  also prevents mask portion  130  from spontaneously inflating after mask portion  130  has been intentionally deflated. Although it is normally closed, valve  150  may be temporarily opened to permit selective inflation and deflation of mask portion  130 . Normally, an air syringe, or other air supply device (not shown), is coupled to end  152  of valve  150 , and in the act of coupling, the air supply device biases the pin  170  so as to separate shoulders  174  (of pin  170 ) and  164  (of body  160 ) and thereby open the valve. The air supply device may then inflate or deflate mask portion  130 . Once the air supply device is decoupled from valve  150 , the biasing force provided by spring  180  automatically closes valve  150  and thereby maintains the current pressure inside of mask portion  130 . End  152  of valve  150  is normally designed to comply with International Standard ISO 594-1 so that it may readily be coupled to standard air supply devices. 
     Although valves such as valve  150  have been in use for many years and have functioned well, there remains a need for providing improved control over the pressure in the inflatable portions of laryngeal mask airway devices as well as in other inflatable devicies. 
     SUMMARY OF THE INVENTION 
     These and other objects are provided by improved inflation valves and by inflatable devices constructed using those valves. 
     Several varieties of laryngeal mask airway devices are durable enough to permit them to be sterilized in an autoclave and reused. For example, the “Classic” laryngeal mask airway device sold by the Laryngeal Mask Company of Cyprus, is guaranteed to survive forty sterilizations, and in practice these devices may generally be sterilized (and reused) more than forty times before becoming too worn for reuse. The “Proseal”, also sold by the Laryngeal Mask Company of Cyprus, may also be sterilized and reused. 
     The sterilization process normally involves exposing the laryngeal mask airway device to a high temperature environment inside an autoclave. The pressure of the environment inside an autoclave typically varies during the sterilization process such that at times the pressure is relatively high and at other times the pressure is relatively low. Laryngeal mask airway devices are normally fully deflated before being placed inside an autoclave for sterilization. If the devices are not fully deflated prior to sterilization, air trapped inside the mask portion can cause the mask portion to expand when the environment inside the autoclave is at a low pressure. Such expansion can sometimes cause the mask portion to burst thereby rendering the laryngeal mask airway device useless. Also, even if the mask portion doesn&#39;t burst, excessive expansion of the mask portion within an autoclave may weaken or permanently deform the mask portion thereby decreasing the device&#39;s useful life or potentially reducing the device&#39;s usefulness. 
     One problem with prior art laryngeal mask airway devices is that practitioners cannot be relied upon to deflate them sufficiently to prevent potentially damaging expansion of the mask portion during sterilization in an autoclave. Also, if a laryngeal mask airway device is exposed to normal atmospheric pressure for several hours after a full deflation, the semi-permeable nature of most mask portions allow them to partially inflate. Such partial inflation can also result in potentially damaging expansion of the mask portion during subsequent sterilization. These problems are most serious for laryngeal mask airway devices that use a relatively soft material for the mask portion (e.g., such as the Proseal). However, the problem potentially affects any reusable (i.e., sterilizable) inflatable device. 
     The invention provides improved inflation valves and inflatable devices constructed with such valves. Valves constructed according to the invention automatically open when exposed to high temperatures. Accordingly, when a laryngeal mask airway device, or other inflatable device (such as an endotracheal tube, a tracheostomy tube, or a balloon catheter), equipped with a valve constructed according to the invention is sterilized, the valve will advantageously automatically open when exposed to the high temperature environment of the autoclave. This allows any gas that may have been previously trapped in the inflated portion of the device to escape through the valve into the autoclave chamber during low pressure portions of the sterilization process. Valves constructed according to the invention thereby automatically protect the inflatable portion of medical devices from undue expansion and wear. 
     In one aspect, the invention provides a laryngeal mask airway device comprising an airway tube, an inflatable mask portion, and a valve. The airway tube can extend from a proximate end,to a distal end. The inflatable mask portion can be fixed to the airway tube. The mask portion can be insertable through the mouth of a patient to an inserted location within the patient. The mask portion can form a seal around the patient&#39;s glottic opening when the mask portion is in the inserted location and inflated. The proximate end of the airway tube can be disposed outside the patient when the mask portion is in the inserted location. The valve can be in fluid communication with the inflatable mask portion. The valve can include a member that is movable between an open position and a closed position. The valve can prevent fluid from escaping the mask portion when the member is in the closed position. The valve can permit fluid to escape the mask portion when the member is in the open position. The valve can include a resilient element. The resilient element can provide a first force that biases the member towards the closed position. The valve can include a temperature sensitive element. The temperature sensitive element can generate a second force that biases the member towards the open position. The first force can be greater than the second force when the ambient temperature is below a first value. The first force can be smaller than the second force when the ambient temperature is above a second value. An end portion of the member can be accessible to an environment external to the valve. The member can be movable to the open position by applying pressure to the end portion of the member. 
     In this aspect, the second force can be substantially equal to zero when the ambient temperature is below the first value. 
     Also in this aspect, the temperature sensitive element can comprise a nickel titanium alloy. 
     Also in this aspect, the temperature sensitive element can be characterized by a first length when the ambient temperature is below the first value, and the temperature sensitive element can be characterized by a second length when the ambient temperature is above the second value, the first length being longer than the second length. 
     Also in this aspect, the valve can include a body, the body defining an internal passage that extends through the body. Also, the body can further define a first shoulder. Also, the member can define a second shoulder, the first and second shoulders being in contact when the member is in the closed position, the first and second shoulders being spaced apart when the member is in the open position. Also, the device can include a cap fixed to one end of the body. Also, the device can include a post fixed to one end of the member. Also, the temperature sensitive element can have a first end, a second end, and a central portion, the first and second ends of the temperature sensitive element being fixed to the cap, the central portion of the temperature sensitive element contacting the post. Also, the post can define a slot, the central portion of the temperature sensitive element extending through the slot. Also, the cap can include a base, a body, and at least one clamp. Also, the clamp can be disposed between a portion of the base and a portion of the body. Also, an end of the temperature sensitive element can be fixed to the clamp. Also, the member can be disposed in the internal passage. Also, an end of the member can be proximate to an open end of the valve. Also, the second value can be greater than or equal to seventy degrees Celsius. 
     In another aspect, the invention provides a medical device comprising a tube, an inflatable structure, an inflation lumen, and a valve. The tube can define an interior passage. The inflatable structure can be fixed to the tube. The inflatable structure can be insertable into an airway of a human patient. The inflatable structure can form a seal with a portion of the airway when inserted into the patient and inflated. The inflation lumen can have a first end and a second end. The first end of the inflation lumen can be coupled to the inflatable structure. The valve can be coupled to the second end of the inflation lumen. The valve can define a closed position and an open position. A fluid flow path can be provided when the valve is in the open position, the fluid flow path extending from an interior of the inflatable structure through the inflation lumen and through the valve. The valve can block the fluid flow path when the valve is in the closed position. The valve can include a temperature sensitive element. The temperature sensitive element can force the valve into the open position when a temperature exceeds a first value. The temperature sensitive element can allow the valve to return to the closed position when the temperature falls below a second value. 
     In this aspect, the valve can include a movable member and a body, a first surface of the movable member contacting a second surface of the body when the valve is in the closed position, the first surface of the movable member being spaced apart from the second surface of the body when the valve is in the open position. Also, the valve can include a spring, the spring biasing the first surface of the movable member towards the second surface of the body. 
     In another aspect, the invention provides a method of automatically protecting an inflatable device during sterilization. The method can include a step of providing the device with a temperature sensitive valve that automatically opens when a temperature exceeds a first value. The method can further include a step of exposing the device to an environment that will sterilize the device, the environment being characterized by a temperature above the first value. When the temperature exceeds the first value, the valve can automatically open and permit fluid in the inflatable device to escape into the environment. 
     In another aspect, the invention provides a medical device including an inflatable structure and a valve. The inflatable structure can be configured for positioning in a human patient. The valve can be in fluid communication with the inflatable structure. The valve can include a member that is movable between an open position and a closed position. The valve can prevent fluid from escaping the inflatable structure when the member is in the closed position. The valve can permit fluid to escape the inflatable structure when the member is in the open position. The valve can include a resilient element. The resilient element can provide a first force that biases the member towards the closed position. The valve can include a temperature sensitive element. The temperature sensitive element can generate a second force that biases the member towards the open position. The first force can be greater than the second force when the ambient temperature is below a first value. The first force can be smaller than the second force when the ambient temperature is above a second value. An end portion of the member can be accessible to an environment external to the valve. The member can be movable to the open position by applying pressure to the end portion of the member. 
     In this aspect, the second force can be substantially equal to zero when the ambient temperature is below the first value. 
     Also in this aspect, the temperature sensitive element can comprise a nickel titanium alloy. 
     Also in this aspect, the temperature sensitive element can be characterized by a first length when the ambient temperature is below the first value, and the temperature sensitive element can be characterized by a second length when the ambient temperature is above the second value. The first length can be longer than the second length. 
     Also in this aspect, the valve can include a body. The body can define an internal passage that extends through the body. Also, the body can define a first shoulder. Also, the member can define a second shoulder. The first and second shoulders can be in contact when the member is in the closed position. The first and second shoulders can be spaced apart when the member is in the open position. Also, the device can include a cap fixed to one end of the body. Also, the device can include a post fixed to one end of the member. Also, the temperature sensitive element can have a first end, a second end, and a central portion. The first and second ends of the temperature sensitive element can be fixed to the cap. The central portion of the temperature sensitive element can contact the post. Also, the post can define a slot. The central portion of the temperature sensitive element can extend through the slot. Also, the cap can include a base, a body, and at least one clamp. Also, the clamp can be disposed between a portion of the base and a portion of the body. Also, the end of the temperature sensitive element can be fixed to the clamp. Also, the second value can be greater than or equal to seventy degrees Celsius. 
     Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description wherein several embodiments are shown and described, simply by way of illustration of the best mode of the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not in a restrictive or limiting sense, with the scope of the application being indicated in the claims. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     For a fuller understanding of the nature and objects of the present invention, reference should be made to the following detailed description taken in connection with the accompanying drawings in which the same reference numerals are used to indicate the same or similar parts wherein: 
     FIG. 1 shows a prior art laryngeal mask airway device. 
     FIG. 2A shows a sectional view of a prior art inflation valve, used with laryngeal mask airway devices, in its normally closed position. 
     FIG. 2B shows a sectional view of the valve shown in FIG. 2A in an open position. 
     FIG. 2C shows a view of the valve taken in the direction of arrow  2 C— 2 C as shown in FIG.  2 A. 
     FIG. 2D shows a sectional view of the valve shown in FIGS. 2A-2C in which sectional views of the body are artificially expanded. 
     FIG. 2E shows a more detailed sectional view of a prior art inflation valve of the type generally illustrated in FIGS. 2A-2D. 
     FIG. 3A shows a sectional view of an inflation valve constructed according to the invention in its normally closed position. 
     FIG. 3B shows a sectional view of the valve shown in FIG. 3A in an open position. 
     FIG. 3C shows a view of the valve taken in the direction of arrow  3 C— 3 C as shown in FIG.  3 A. 
     FIG. 3D shows the post of the valve shown in FIGS. 3A-3C prior to assembly into the valve. 
     FIG. 3E shows a view of the post that is rotated ninety degrees from the view shown in FIG.  3 D. 
     FIG. 3F shows a more detailed sectional view of a valve constructed according to the invention of the type generally illustrated in FIGS. 3A-3E. 
     FIG. 3G shows an end view of one embodiment of the base shown generally in FIGS. 3A,  3 B, and  3 C. 
     FIGS. 3I and 3H show side views of the base shown in FIG.  3 G. 
     FIGS. 3J and 3K show end and side views, respectively, of one embodiment of the post shown generally in FIGS. 3A-3F. 
     FIGS. 3L and 3M show end and side views, respectively, of the post that are rotated ninety degrees from the views shown in FIGS. 3J and 3K. 
     FIG. 4 shows one embodiment of a clamp for use with valves constructed according to the invention. 
     FIG. 5A shows a sectional view of another embodiment of an inflation valve constructed according to the invention in its normally closed position. 
     FIG. 5B shows a sectional view of the valve shown in FIG. 5A in an open position. 
     FIG. 6 shows one embodiment of a temperature sensitive element for use with valves constructed according to the invention. 
     FIG. 7A shows a sectional view of another embodiment of an inflation valve constructed according to the invention in its normally closed position. 
     FIG. 7B shows a sectional view of the valve shown in FIG. 7A in an open position. 
     FIG. 8A shows a sectional view of another embodiment of an inflation valve constructed according to the invention in its normally closed position. 
     FIG. 8B shows a sectional view of the valve shown in FIG. 8A in an open position. 
     FIG. 8C shows a magnified view of a portion of the pin and body enclosed within the ellipse  8 C as shown in FIG.  8 A. 
     FIG. 8D shows a magnified view of a portion of the pin and body enclosed within the ellipse  8 D as shown in FIG.  8 B. 
     FIG. 9 shows a laryngeal mask airway device constructed according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3A shows a sectional view of a valve  250  constructed according to the invention in its normally closed position (i.e., a position in which valve  250  prevents fluid from flowing between ends  154  and  252  of valve  250  or at least provides resistance to fluid flowing between ends  252  and  154 ). FIG. 3B shows a sectional view of valve  250  in an open position (i.e., a position in which valve  250  permits fluid to flow between ends  154  and  252  of valve  250 ). FIG. 3F shows a more detailed sectional view of a valve constructed according to the invention. 
     When exposed to normal room temperatures, valve  250  is normally in the closed position shown in FIG.  3 A. When exposed to high temperatures, valve  250  automatically transitions to an open position such as that shown in FIG.  3 B. Valve  250  may of course also be opened manually, even at room temperatures, for example by coupling an air supply device, such as a syringe (not shown), to end  252  of valve  250 . End  252  of valve  250  may be configured so as to comply with International Standard ISO 594-1 to facilitate coupling to standard air supply devices. 
     As shown, valve  250  includes a prior art valve  150  (as shown in, e.g., in FIG. 2A) as well as a hollow cap  300 , which is coupled to end  152  valve  150 . Cap  300  includes a base  310 , a body  330 , and two clamps  340 , and cap  300  defines a central channel  390 . Valve  250  also includes a post  350  and a temperature sensitive wire  370  disposed in channel  390 . FIG. 3C shows a view of cap  300  taken in the direction of arrow  3 C— 3 C as shown in FIG.  3 A. 
     As shown most clearly in FIGS. 3A and 3B, base  310  engages end  152  of prior art valve  150 . Body  330  engages base  310 , and clamps  340  are trapped, or clamped, between base  310  and body  330 . More specifically, and as shown best in FIG. 3C, base  310  defines an annular extension  312 , and clamps  340  are trapped between the outer wall of extension  312  and the inner wall of body  330 . Base  310 , body  330 , and clamp  340  cooperate so that cap  300  effectively provides a relatively rigid structure that is fixed relative to valve  150  such that channel  390  of cap  300  communicates with channel  169  of body  160 . 
     One end of post  350  is fixed to, or rests on, pin  170  of the prior art valve  150 , and post  350  extends through hollow interior channel  390  towards end  252  of valve  250 . The two ends of temperature sensitive wire  370  are fixed to, or held by, clamps  340 , and the center of wire  370  is threaded through a slot  352  defined in post  350 . 
     FIGS. 3D and 3E show two views of post  350  (prior to its assembly into valve  250 ) and illustrate the slot  352  through which wire  370  is threaded. The view of post  350  shown in FIG. 3D is rotated ninety degrees from the view shown in FIG.  3 E. The slot  352  is shown best in FIG.  3 E. As shown in FIG. 3D, the floor  354  of the slot  352  defines a curved profile. The floor  354  of slot  352  has its lowest points  356  proximate to the outer perimeter of post  350  and has its highest point  358  near the center of post  350 . A central portion of temperature sensitive wire  370  rests on the curved floor  354  of slot  352  as shown in FIG.  3 A. Providing slot  352  with such a curved floor advantageously prevents wire  370  from contacting a “sharp corner” of post  350  and thereby reduces wear on temperature sensitive wire  370 . 
     Temperature sensitive wire  370  is fabricated so that its length decreases when exposed to high temperatures and so that its length increases (or so that wire  370  returns to its original, or near original, un-contracted length) when exposed to normal room temperatures. As shown in FIG. 3B, when the length of wire  370  shrinks, it biases post  350  and thereby pushes pin  170  so as to compress spring  180  and thereby open valve  250 . Since shoulders  174  (of pin  170 ) and  164  (of body  160 ) are separated from one another, the position of pin  170  and post  350  shown in FIG. 3B may be regarded as an open position. As shown in FIG. 3A, when the length of wire  370  increases (or returns to its original, or near original, un-contracted length), it allows spring  180  to bias pin  170  and post  350  upwards (in the orientation of valve  250  shown in FIG. 3A) to thereby close valve  250 . The position of pin  170  and post  350  shown in FIG. 3A may be regarded as a closed position. 
     In its expanded condition, wire  370  may be under some amount of tension. As long as the resultant force (i.e., a force which is parallel to and opposite to the force generated by spring  180 ) generated by the wire  370  is smaller than the force generated by spring  180 , the spring  180  can bias the pin  170  to a closed position thereby closing the valve. Alternatively, when wire  370  is in its expanded condition, it may define some slack so that the force applied by wire  370  to post  350  is nominal or effectively zero. 
     One preferred class of materials for fabricating temperature sensitive wire  370  are nickel titanium alloys. These materials, commonly known as NITINOL, possess a variety of unusual but well documented properties, including the ability to shrink or contract when heated and to expand when cooled. More specifically, these materials generally undergo a phase transformation in their crystal structure when cooled from a stronger, high temperature form (Austenite) to a weaker, low temperature form (Martensite). As such, these materials effectively provide two distinct configurations. Also, raising or lowering the temperature by just a few degrees is normally sufficient to cause the material to shift from one configuration to the other. In one preferred embodiment, (1) temperature sensitive wire  370  transitions from its low temperature phase (or its longer configuration in which valve  250  is closed) to its high temperature phase (or its shorter configuration in which valve  250  is open) at about seventy degrees Celsius and (2) temperature sensitive wire  370  transitions from its high temperature phase (or its shorter configuration in which valve  250  is open) to its low temperature phase (or its longer configuration in which valve  250  is closed) at about fifty degrees Celsius. Such hysteresis is common in nickel titanium alloys. Also, it will be appreciated that other temperature ranges could be used (e.g., ninety degrees Celsius, or a human body temperature, could alternatively be used as the temperature at which valve  250  transitions from its normally closed position to its open position). Also, wire  370  is preferably configured so that its length changes by about four percent when it changes from its low temperature phase to its high temperature phase. 
     At the room temperatures in which medical devices are normally used with patients, valve  250  is normally closed. However, even at room temperatures in which valve  250  is normally closed, valve  250  may be opened in the customary fashion, e.g., by coupling an air supply device such as an air syringe to one end of the valve, to permit inflation or deflation of the medical device. When a device such as an air syringe is coupled to the valve, the syringe depresses post  350  to open the valve. Depression of post  350  (e.g., by an air syringe) to open valve  250  is generally possible because an end of post  350  is accessible to the environment external to valve  250  (in a fashion similar to that in which an end of pin  170  is accessible to an environment external to prior art valve  150 ). Preferably, temperature sensitive element  370  fits loosely within slot  352  so that depression of post  350  by an air syringe does not cause significant movement of wire  370 . 
     Coupling or decoupling an air supply device to or from end  252  may cause some rotation of post  350 . If post  350  is allowed to freely rotate with respect to base  310 , such rotation may damage temperature sensitive element  370 . Accordingly, it may be preferable to prevent post  350  from rotating with respect to base  310  or clamps  340 . One way to prevent post  350  from rotating with respect to base  310  is to elongate the aperture of base  310  through which post  350  extends and to also elongate the cross section of post  350 . FIGS. 3G-3M illustrate such a configuration of post  350  and base  310 . More particularly, FIG. 3G shows an end view of one embodiment of base  310  in which the central channel  390 , through which post  310  extends when the valve is assembled, is elongated. FIGS. 3H and 31 show two side views of base  310 . FIGS. 3J-3M show different views of post  350 . As shown, the cross section of the portion of post  350  that extends through base  310  is not circular and is instead elongated, or generally elliptical. When the valve is assembled, any substantial rotation (e.g., more than about 5 degrees) of post  350 , will cause the post to contact the walls of the channel  390  defined by base  310  and thereby prevent post  350  from rotating further with respect to base  310 . 
     Clamps  340  may be metallic (e.g., fabricated from brass) and the post  350  and the components of cap  300  may be made from plastic. However, it will be appreciated that a variety of other materials may be used to fabricate valve  250 . For example, the entire valve could be made of one or more metals such as aluminum. FIG. 4 shows one embodiment for fabricating clamp  340 . In this embodiment, clamp  340  is a metallic block that defines a slot  342 . During assembly, one end of temperature sensitive wire  370  is inserted into slot  342  and then clamp  340  is squeezed or crimped so that clamp  340  effectively anchors, or permanently holds onto, the end of wire  370 . It will be appreciated however that many other methods and structures may be used for anchoring wire  370  to a fixed location in valve  250 . 
     While the preferred embodiment of valve  250  includes a cap that is coupled to a standard prior art valve, as has been generally discussed above in connection with FIGS. 3A-3F, it will be appreciated that numerous other embodiments of valve  250  are embraced within the invention. FIGS. 5A and 5B illustrate an example of another embodiment of a valve  250  constructed according to the invention. In this embodiment, rather than using a cap for mounting temperature sensitive wire  370 , the temperature sensitive wire  370  is fixed to the body  160  of the valve. FIG. 5A shows valve  250  in its normally closed position. FIG. 5B shows valve  250  when shrinkage of temperature sensitive wire  370 , caused by exposure to high temperature, caused valve  250  to move into an open position. 
     It will be appreciated that the ends of a temperature sensitive wire  370  may be fixed, or anchored, to a structure such as body  160  in numerous ways such as by clamping, welding, adhesives, etc. Also, it may be advantageous to provide the ends of wire  370  with enlarged structures, or anchors,  372 , as shown generally in FIG.  6 . Including such anchors  372  may facilitate attachment of wire  370  to a structure such as clamp  340  or the body of a valve. It will further be appreciated that although a “wire” is a preferred configuration for temperature sensitive element  370 , the temperature sensitive element  370  may be configured in other shapes and forms without departing from the invention. 
     FIGS. 7A and 7B illustrate an example of yet another embodiment of a valve  250  constructed according to the invention. In this embodiment, rather than attaching a cap to end  152  (as shown for example in FIGS.  3 A- 3 F), a simpler cap or L-bracket  300  is attached to end  154  of valve  250 . Temperature sensitive element  370  is coupled between an end of bracket  300  and pin  170 . FIG. 7A shows valve  250  in its normally closed position. FIG. 7B shows valve  250  when shrinkage of temperature sensitive element  370 , caused by exposure to high temperature, caused valve  250  to move into an open position. It will be appreciated that temperature sensitive element  370  may be fixed to pin  170  in numerous ways. For example, element  370  may be fixed to a notch (not shown) in the lower part of pin  170  or may be otherwise adhered or attached to pin  170 . Similarly, element  370  may be attached to bracket  370  in numerous ways. For example, element  370  may be looped over an end of bracket  300 , may be clamped, crimped, or anchored to bracket  300 , or may be otherwise attached or adhered to bracket  300 . 
     FIGS. 8A and 8B illustrate yet another embodiment of a valve  250  constructed according to the invention. FIG. 8A shows valve  250  in its normally closed position. FIG. 8B shows valve  250  in an open position. In this embodiment, temperature sensitive elements  370  expand upon exposure to increased temperature and force shoulders  174  (of pin  170 ) and  164  (of body) apart to thereby open the valve. 
     FIG. 8C shows a magnified view of the portion of pin  170  and body  160  enclosed within the ellipse  8 C as shown in FIG.  8 A. Similarly, FIG. 8D shows a magnified view of the portion of pin  170  and body  160  enclosed within ellipse  8 D as shown in FIG.  8 B. As shown in FIGS. 8C and 8D, in this embodiment, shoulder  174  of pin  170  defines one or more wells, or recesses,  179 . Temperature sensitive elements  370  are disposed in the wells  179 . At normal room temperatures, temperature sensitive elements are sufficiently small to fit within the wells  179  so that contact between shoulders  174  (of pin  170 ) and  164  (of body) form a seal and effectively close valve  250 . However, when the ambient temperature increases above a selected value (e.g., seventy or ninety degrees Celsius), temperature sensitive elements  370  expand beyond wells  179  and force shoulders  174  and  164  apart thereby opening valve  250 . In this embodiment, temperature sensitive elements  370  may be manufactured from plastic materials with relatively high coefficients of thermal expansion such as nylon or low density polyethylene or metallic materials with high coefficients of thermal expansion such as zinc, lead, magnesium, aluminum, tin, and their alloys. 
     FIG. 9 shows a laryngeal mask airway device  400  constructed using valve  250  according to the invention. The valve  250  used in device  400  may be any of the valves explicitly disclosed herein or any other valve that automatically opens at high temperatures. In operation, valve  250  permits laryngeal mask airway device  400  to be inflated and deflated in its customary fashion (e.g., by coupling an air syringe to an end of valve  250 ), and device  400  may be used with patients in the customary fashion. However, when device  400  is exposed to high temperatures (e.g., in the sterilizing environment of an autoclave), valve  250  automatically opens thereby advantageously allowing any gas trapped in inflatable device  400  to escape. Valve  250  may be used with any inflatable medical device such as a laryngeal mask airway device, an endotracheal tube, or a tracheostomy tube. Also, in addition to airway type medical devices, valve  250  may also be used with other types of inflatable medical devices such as balloon catheters (e.g., such as angioplasty catheters or other cardiac catheters). It will be appreciated that valve  250  may be used with any inflatable medical device to protect the device from excessive expansion during sterilization. 
     Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted in an illustrative and not a limiting sense. For example, valves constructed according to the invention have been discussed as including prior art valves  150  of the type illustrated in FIGS. 2A-2E. However, it will be appreciated that valve  150  is merely exemplary and that the invention encompasses inflatable devices constructed using any valve that automatically opens at high temperature. Valves have also been discussed herein as preventing fluid from flowing through the valve when in the closed position. It will be appreciated that any valve will leak by some amount even when in the closed position and that phrases such as “preventing fluid from escaping” or “preventing fluid from flowing” do not imply that a closed valve prevents all leakage and merely means that a closed valve provides more resistance to fluid flow than does an open valve.