Patent Publication Number: US-7220273-B2

Title: Control of airflow to an inflatable thermal device

Description:
This is a divisional of application Ser. No. 09/546,078, entitled CONTROL AND DETECTION OF A CONDITION BETWEEN AN INFLATABLE THERMAL DEVICE AND AN AIR HOSE IN A CONVECTIVE WARMING SYSTEM, invented by Van Duren et al., and filed on April 10, 2000, now U.S. Pat. No. 6,447,538 which is a continuation in part of prior application Ser. No. 09/138,774, entitled DETECTION OF A CONDITION BETWEEN AN INFLATABLE THERMAL DEVICE AND AN AIR HOSE IN A CONVECTIVE WARMING SYSTEM, invented by Van Duren et al., and filed on Aug. 24, 1998 now U.S. Pat. No. 6,126,681. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to pressurized thermal systems that regulate human core temperature by convecting pressurized, thermally regulated air. More particularly, the invention relates to inflatable thermal blankets and the like that are used, for example, in a medical setting to deliver a bath of pressurized air which is heated, cooled, or ambient temperature, for the treatment of hypothermia or hypothermia. In particular, pressurized, thermally regulated air is used to inflate such a device and is expelled therefrom onto a person or animal. Still more particularly, the invention relates to controlling the flow of pressurized air through the end of an air hose in response to coupling and decoupling the end to the inlet port of an inflatable thermal device. 
     The International Electrotechnical Commission has promulgated a new standard (IEC 601-2-35) entitled Particular requirements for safety of blankets, pads and mattresses, intended for heating in medical use. This standard imposes requirements on the design and operation of convective warming systems. In particular, clause 46.101 states: “If omission of a part, or the interchange of parts of a multi-part heating device, will cause a safety hazard, the heating device shall be designed such that heat will be supplied only if all parts of the heating device are correctly positioned.” This requirement is intended to prevent human or equipment error leading to patient injury. 
     In convective warming systems, a pressurized thermal device is used to deliver a bath of pressurized, thermally-regulated air to a person, animal, or thing. The device is inflated with the pressurized, thermally-regulated air and has one or more surfaces adapted for expelling the air onto a person. Such devices may lie on a person, around a person, or under a person. U.S. Pat. Nos. 5,324,320 and 5,405,371, for example, describe inflatable thermal blankets that lie on a person, expelling pressurized, warmed air through a lower surface that faces the person. U.S. Pat. No. 5,300,101 describes another inflatable thermal device that lies around the sides and at least one end of a person. Other kinds of inflatable thermal devices are contemplated, including those lying under a person. Therefore, when used, the term “inflatable thermal device” is intended to invoke any and all blankets, pads, mattresses, covers, and equivalent structures that operate as just described. 
     Typically, the inflatable thermal devices of interest convect pressurized air in response to a pressurized flow of warmed, cooled, or ambient temperature air that is provided, for example, from a heater/blower unit through an air hose. Typically the inflatable device includes one or more inlet ports that receive one end of the air hose. The other end of the air hose is received in the heater/blower unit. When the heater/blower unit is turned on, air is warmed in the unit and pumped from the unit through the air hose to inflate the inflatable thermal device, whence the air is exhausted to warm or cool a person. Such devices may exhaust the air through a plurality of punched holes, through porous material, or through air permeable material. 
     One hazard in convective warming systems that use inflatable devices is the risk of overheating or burning a person. In the first instance, the air temperature may exceed a level necessary for proper treatment. In the second instance, the end of the air hose that is received in an inlet port may become dislodged and repositioned in such a way as to direct the pressurized, heated air flow directly onto a person. It is these hazards that are contemplated by the IEC standard. To date, means for detecting and mitigating these hazards have not been incorporated into the convective warming systems described above. Furthermore, in addition to the hazards contemplated by the new IEC standard, there is an operating deficiency common to many commercially available convective warming systems. This deficiency lies in the dependence of the air flow temperature at the distal end of an air hose on several environmental and design conditions which prevent accurate estimation of air hose outlet temperature. 
     The commercially available heater/blower units for convective warming systems include a heater and a blower which operate to provide a steady stream of temperature-conditioned air at a given mass flow. The temperature of the heated air ducted from the heater/blower unit through an air hose is tightly controlled at the heater/blower unit end of the air hose; however, the temperature of air flow introduced into the inflatable thermal device is a function of several factors, including, but not limited to: 1.) the thermal capacity of the unit; 2.) the blower capacity; 3.) the length, thermal conductivity, and thermal emissivity of the air hose between the unit and the device; 4.) the fluid flow resistance of the device; and, 5.) the ambient conditions, of which temperature and external air velocity are the most important. 
     The exhaust (output) temperature of the flow of air leaving a heater/blower unit is generally tightly controlled by a unit temperature controller. The temperature controller continually senses the output temperature at a port in the unit where the proximal (near) end of the air hose is received and adjusts the heater unit power to maintain the output temperature at constant setting. The temperature of the air flow at the distal (far) end of the air hose (that is, the inlet temperature to the inflatable thermal device), however, depends greatly on the conditions listed above. 
     With most of the presently available heater/blower systems, it is also possible to interconnect the blower units, hoses, and thermal blankets of different manufacturers. Because these components may not have been designed to work together, and because there are not always common standards, the patient can be inadvertently supplied with air at inappropriate flow rates and temperatures. Not only can the patient be harmed, it is also possible to damage the equipment. Further, some users may knowingly use equipment that is not designed to work together out of convenience. Clearly visible electrical contact points permit operators to bypass interlock safeguards. The concern for the improper use of equipment must be tempered with the ability to warm patients in emergency situations. 
     Accordingly there is a need to: 1.) prevent heater/blower unit misuse when the inflatable thermal device has been disconnected from the air hose; 2.) provide better control of air flow temperature at the distal end of the air hose irrespective of ambient conditions, resistive load of the inflatable thermal device, or heater/blower unit capability; and 3.) meet the requirements of the IEC standard. 
     SUMMARY OF THE INVENTION 
     The invention is based on the critical realization that the junction between the distal (far) end of an air hose and an inlet port of an inflatable thermal device provides a location where the continuity of the air flow path can be regulated. 
     In this regard, flow of air to the inflatable thermal device is controlled mechanically, with the insertion of the distal end of the air hose into the inflatable thermal device. Several valve mechanisms can be used to block air flow from the air hose when the hose is not properly seated in the inlet port. When inserted, the valves are forced open to provide air to the inflatable thermal device. 
     Accordingly, it is an object to invent a convective warming system that includes a pressurized thermal device with the ability to react to air flow conditions at a point where an air flow is provided through an inlet port of the device. 
     Another object is to disable, prevent, or attenuate the operation of a convective warming system when the inflatable thermal device becomes detached from a heater/blower unit. 
     These and other objects and advantages of this invention will become evident when the following detailed description is read in conjunction with the below-described drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 . Is an illustration of a convective warming system in which the invention may be embodied; 
         FIG. 2  is a block diagram showing the elements of a convective warming system; 
         FIGS. 3A and 3B  illustrate an air hose, an inflatable thermal device and elements of a presence sensor that monitors continuity of the connection between the distal end of the air hose and an inlet port of the device; 
         FIGS. 4A and 4B  illustrate the elements of  FIGS. 3A and 3B , with the addition of an airflow sensor located at the inlet port; 
         FIGS. 5A–5D , illustrate the elements of  FIGS. 3A and 3B  with the addition of an airflow sensor located in the distal end; 
         FIGS. 6A and 6B  illustrate an alternate embodiment of the presence sensor of  FIGS. 3A and 3B ; 
         FIG. 7  illustrates another alternate embodiment of the presence sensor of  FIGS. 3A and 3B ; 
         FIGS. 8A and 8B  illustrate how the proximal end of the air hose may be coupled to a heater/blower unit; 
         FIG. 9  shows a presence sensor in an inflatable thermal device in which an inlet port is provided as a sleeve; and 
         FIGS. 10A and 10B  show an alternate embodiment of the presence detector of  FIG. 9 . 
         FIGS. 11A through 11C  illustrate the inflatable thermal device where the inlet port includes a hose card. 
         FIGS. 12A through 12C  illustrate an alternate aspect of the air hose of  FIG. 11A  or the air hose of  FIGS. 6A ,  6 B,  7 ,  10 A, and  10 B. 
         FIGS. 13A and 13B  illustrate a convective warming system using an electronic identification tag. 
         FIGS. 14A ,  14 B,  15 A– 15 C,  16 A, and  16 B illustrate alternate embodiments of mechanical solutions to the problem of controlling air flow to an inflatable thermal device according to the invention. 
         FIG. 17  is a flowchart illustrating a method for controlling air flow in a system including an inflatable thermal device, corresponding to  FIGS. 14A–14B ,  15 A– 15 C, and  16 A– 16 B. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a convective warming system that is operated to control the body temperature of a person by convecting thermally-regulated air from an inflatable thermal device in the direction of the person&#39;s skin. The convective warming system of  FIG. 1  provides a stream of pressurized, thermally-regulated air to an inflatable thermal device through an inlet port of the device. In  FIG. 1 , the inflatable thermal device is an inflatable thermal blanket, of the type sold by Augustine Medical, Inc. under the BAIR HUGGER® trademark. This, however, is for purposes of illustration only. In fact, any and all equivalent inflatable thermal devices including blankets, pads, mattresses, covers, and equivalent structures are intended to enjoy the benefits of this invention. 
     With greater specificity, the convective warming system of  FIG. 1  includes an inflatable thermal device  10  having one or more inlet ports through which a flow of pressurized, thermally-regulated air is admitted to inflate the inflatable thermal device  10 . One such inlet port is indicated by reference numeral  11 . In the BAIR HUGGER® family of inflatable thermal blankets, inlet ports typically comprise an opening into an inflatable structure and a stiff planar member of cardboard having an aperture. The planar member of cardboard is mounted to the inflatable structure such that the aperture in the member is aligned with the opening in the inflatable structure. The planar member is commonly referred to as a “hose card” because it provides a flat, card-like structural element that receives and supports the distal end of an air hose when the distal end is joined, mated, coupled or received in the inlet port. However, this invention is not intended to be limited to an inflatable thermal device with such inlet ports. Furthermore, an inflatable thermal device may include more than one inlet port. In this regard, many models of inflatable thermal devices have two—and sometimes more—inlet ports located at various positions in order to provide flexibility in arranging the elements of a convective warming system. 
     In the convective warming system of  FIG. 1 , the inflatable thermal device  10  is inflated by a stream of pressurized, thermally-regulated (warmed or cooled) air provided through an air hose  12  having a distal (far) end  14  and proximal (near) end  15 . The distal end  14  is joined, mated, coupled, or received in one of the inlet ports of the inflatable thermal device  10 . In  FIG. 1 , the distal end  14  is received in the inlet port  11 . In other words, the inlet port  11  and the distal end  14  form a junction through which an air flow is provided to inflate the inflatable thermal device  10 . A heater/blower unit  18  generates and provides a flow of pressurized, thermally-regulated air (hereinafter referred to as “an airflow”). In this regard, the unit  18  includes a port  19  in which the proximal end  15  of the air hose  12  is received. Through the port  19 , the proximal end  15  is coupled, mated, received in, or otherwise joined to an outlet of a blower  20 . The unit  18  includes a control unit  21  with user-accessible controls that may be used to set levels or magnitudes of air flow heat and air flow velocity. A signal for air flow velocity is provided by the control unit  21  on signal path  22  where it is coupled to the blower  20  to control the speed of a blower motor (not shown) that propels air through the blower  20 . The control unit  21  further generates a signal on signal path  23  that controls the operation of a heater  24  disposed near the outlet of the blower  20  for heating the air flow. Heater/blower units with user-accessible controls as just described are commercially available. Examples are the 200, 500, and 700 series warming units available from Augustine Medical, Inc. 
     In the example selected for illustration of the convective warming system of  FIG. 1 , the inflatable thermal device  10  is placed on a person  26 . This is not intended to limit the application of this invention to warming only or to use with humans. Indeed, it may be used in any system that thermally regulates persons, animals, or things using an inflatable thermal device. 
     Refer now to  FIG. 2 . In  FIG. 2 , a convective warming system includes an inflatable thermal device (not shown) having one or more inlet ports, one of which is indicated by reference numeral  11 . The distal end  14  of the air hose  12  is intended to be coupled to or received in the inlet port  11 ; however, these elements are shown separated in  FIG. 2 . The proximal end  15  of the air hose  12  is received in the port  19  of the heater/blower unit  18 . The just-described elements may be combined with a combination of elements that operate cooperatively to detect a condition between the distal end  14  of the air hose  12  and the inlet port  11  of the inflatable thermal device. These elements include a first circuit element  40  that is disposed in, on, at or near the inlet port  11 . For example, the first circuit element  40  may be formed an as integral part of a hose card  30 . A second circuit element  42  is located in, on, at, or near the distal end  14  of the air hose  12 , and a signal path including one or more signal conductors  43  extends in or along the air hose  12  to the proximal end  15 . At or near the proximal end  15  of the air hose  12 , the signal path  43  is connected at connector  44  to the control unit  21  of the heater/blower unit  18 . The combination of elements  40 ,  42  and  43  provides a circuit for detecting a condition that may develop or exist between the distal end  14  of the air hose  12  and the inlet port  11 . In other words, these elements enable the generation, conduction, or detection of a signal that represents the condition. Such a condition may be embodied, for example, in the disengagement of the distal end  14  from the inlet port  11  while the heater/blower unit  18  is operating. Another condition, for example, could include a change in the temperature of the air flow through the distal end  14  or the inlet port  11 , or through the junction formed between the distal end  14  and the inlet port  11  while the heater/blower unit  18  is operating. Yet another condition may be a change in the air flow velocity through the distal end  14  or the inlet port, or through the junction formed between the distal end  14  and the inlet port  11  while the unit  18  is operating. In this latter regard, the inverse of the condition would correspond to a decrease in the air flow resistance or a decrease in the air pressure at the distal end  14  of the air hose  12  or the inlet port  11 , or in the junction between the distal end  14  and the inlet port  11  while the unit  18  is operating. Whatever the condition or conditions that these elements are deployed to detect, sensing is provided by cooperative operation between the first circuit element  40  and the second circuit element  42  when the distal end  14  is joined, mated, coupled or received in the inlet port  11 . In this regard, the junction formed between the distal end  14  and the inlet port  11  brings the first and second circuit elements  40  and  42  into close proximity and/or alignment. For so long as the proximity and/or alignment is maintained while the heater/blower unit  18  is operating, a first indication or signal may be generated and conducted on the signal path  43  to the control unit  21 . A change in the condition is sensed by the cooperative operation of the first and second circuit elements  40  and  42 , with the change in condition causing a change in the signal conducted on  43 . A change in the signal conducted on  43  that is observed by the control unit  21  while the heater/blower unit  18  is operating causes the control unit  21  to take any one or more of a number of actions. First, the control unit  21  may simply cause the generation of a perceptible indication. In this regard, an indicator  46  may provide a visual and/or audible indication of a changed condition. In addition, or alternatively, the control unit  21  may respond to a change in condition by changing the motor speed of the blower  20  and/or the temperature of the warming element  24 . Further, the control unit  21  may be designed or adapted to shut down or stop the operation of the heater/blower unit  18  altogether, or to place it in a standby state during which the temperature and/or velocity of the flow of air may be reduced. 
     The cooperative operation of the first and second circuit elements can also provide a “first necessary condition” for starting the heater/blower unit  18 , preventing it from being turned on, or becoming fully operational after being turned on, in response to disconnection or non-connection of the distal end  14  and the inlet port  111  prior to operation of the heater/blower unit  18 . Stated another way, the heater/blower unit  18  may be turned on, or be fully operational only upon detection of joinder, coupling, or mating of the distal end  14  with the inlet port  11 . 
       FIGS. 3A and 3B  illustrate how mating of the air hose distal end with the inlet port is detected and indicated. Although these figures illustrate an inlet port of a certain construction, those skilled in the art will realize that the principles represented in these figures can be applied to other air hose/inlet port configurations. In  FIGS. 3A and 3B , the hose card  30  is shown mounted on the inflatable thermal device  10  at the inlet port  11 . The distal end  14  of the air hose has mounted to it a mechanism that aligns the distal end  14  with the inlet port  11  thereby to join, couple, or mate these elements, or otherwise form a junction between them. The mechanism includes a planar member  50  having generally the same shape and construction as the hose card  30  with the addition of an extending edge  52  that transitions into a lip  53 . The extending edge  52  extends substantially along three sides of the periphery of the planar member  50  so that the distal end  14  can be joined, mated, coupled or received in the inlet port  11  by engaging the edges  31  of the hose card  30  between the lip  53  and a surface of the planar member  50 . In  FIGS. 3A and 3B , a first circuit element  55  is incorporated into the structure of the hose card  30  laterally of the opening in the hose card  30  that communicates with the inlet port  11 . A second circuit element  57  is disposed in the planar member  50  laterally of the opening in the distal end  14  of the air hose  12 . One or more signal conductors  58  are disposed in (or on) the air hose  12 , extending from the distal end  14 , along the air hose  12  toward its proximal end (not shown in these figures). Integration of signal wires into an air hose is within the ambit of modern manufacturing technology. Reference is given, for example, to vacuum cleaner hoses with embedded power conductors. In the figures, two electrical wires  58   a  and  58   b  are shown: their purpose is to conduct signals to the control unit  21 . When the hose card  30  is received between the lip  53  and the planar member  50  so that the opening in the distal end  14  is aligned with the inlet port  11 , the first circuit element  55  and the second circuit element  57  cooperate to complete or close a circuit between the one or more conductors  58   a  and  58   b  that is connected to the control unit  21 . Many possible configurations of this circuit are possible for implementing as much of the invention as is illustrated in  FIGS. 3A and 3B . For example, the first circuit element  55  may comprise a magnetic member and the second circuit element  57  may comprise a reed switch or a Hall effect device. In this case, when the first and second circuit elements  55  and  57  are placed in close proximity by mating of the distal end  14  with the inlet port  11 , the magnetic member  55  causes the reed switch to close, connecting the two electrical conductors  58   a  and  58   b , thereby creating a signal pathway along which a signal may be conducted. Conversely, when the distal end  14  is disengaged from the inlet port  11 , the first and second circuit members  55  and  57  will be moved apart, causing the reed switch to open, which will disable, interrupt or open the signal path just described. This of course will prevent the conduction of a signal. Other mechanisms may be used for the first and second circuit elements  55  and  57  and for the one or more conductors  58   a  and  58   b . For example, the first circuit element  55  may comprise a spring-loaded bar of conductive material, while the second circuit element  57  may comprise two spaced-apart terminals or posts to which the electrical conductors  58   a  and  58   b  are respectively connected. When the first and second circuit elements  55  and  57  are in close proximity, it is contemplated that the conductive bar in the hose card  30  would span and contact the posts, providing a conductive path therebetween. In yet another alternate implementation, the first circuit element  55  may comprise a spring-loaded, protruding member and the second circuit element  57  could comprise a mechanical switch that is operated by the protruding member when the distal end  14  is joined to the inlet port  11 . In yet another implementation, the circuit could be an optical one in which the conductors  58   a  and  58   b  are optical fibers that terminate in optical connectors in the second circuit element  57 . In this case, the first circuit element  55  could include an optical coupler that would complete an optical signal path between the ends of the two optical conductors. Alternatively, means exist for implementing an optical circuit using a single optical fiber terminated at the second circuit element  57  and a mirror incorporated in the first circuit element  55 . 
     The first and second circuit elements  55  and  57  in  FIGS. 3A and 3B  operate cooperatively to provide a sensor-like function. In this regard, the sensor could be termed a “presence” sensor in that it senses the presence of the inlet port  11  from the standpoint of the distal end  14 , or, conversely, it senses the presence of the distal end  14  with respect to the inlet port  11 . From another point of view, the first and second circuit elements operate cooperatively as a switch with OPEN and CLOSED positions. The OPEN position would indicate separation or disconnection between the distal end  14  and the inlet port  11  or discontinuity of the junction formed between the distal end  14  and the inlet port  11 . The CLOSED position, on the other hand, would indicate joining or connection of the distal end  14  with the inlet port  11 , or continuity of the junction formed therebetween. 
       FIGS. 4A and 4B  illustrate how the information provided by the simple two-state switch of  FIGS. 3A and 3B  can be enriched by provision of an air flow sensor at the junction formed between the distal end  14  and inlet port  11 . In the description an Aair flow sensor≅ is a sensor that detects one or more air flow conditions and causes generation of a signal having a component that reports the magnitude of the sensed conditions(s). The air flow conditions may include, for example, temperature and velocity. In  FIGS. 4A and 4B , the first circuit element comprehends a first conductive contact element  55   a , a second conductive contact element  55   b  and a sensor  55   c . The first and second elements  55   a  and  55   b  are physically and electrically connected to the sensor  55   c , which is disposed in the opening of the hose card  30  in alignment with the inlet port  11 . Again, the elements  55   a ,  55   b , and  55   c  are integrated into the structure of the hose card  30 , although this is not intended to limit the implementation of a sensor at the junction between the distal end  14  and the inlet port  11 . The second circuit element includes first and second conductive contact elements  57   a  and  57   b  disposed in the planar member  50  laterally of the opening in the distal end  14 . When the planar member  50  fully engages the hose card  30  to join the distal end  14  with the inlet port  11 , the contact element  55   a  mechanically and electrically contacts the contact element  57   a , while the contact element  55   b , physically and electrically contacts the contact element  57   b . The electrical conductors  58   a  and  58   b  are connected, respectively, to the second circuit element contact elements  57   a  and  57   b . Now, when the hose card  30  is engaged by the planar member  50 , the presence sensor function will be performed by completion of an electrical signal path comprising  58   a ,  57   a ,  55   a ,  55   c ,  55   b ,  57   b , and  58   b . In addition, the sensor  55   c , being disposed in the junction formed between the distal end  14  and the inlet port  11  provides the ability to sense and indicate characteristics of the air flow in the junction. In this regard, assuming that the sensor  55   c  comprises a thermocouple, the temperature of the air flow could be measured and reported in the form of a signal. The sensor  55   c  could also be configured to sense the velocity of the air flow at the same point using a hot-wire anemometer, for example. Moreover, two sensors and two circuits could be incorporated in the manner illustrated in  FIGS. 4A and 4B  to indicate presence, air flow temperature, and air flow velocity, or any combination thereof. Manifestly, optical elements exist which may be assembled using  FIGS. 4A and 4B  and the description just given to implement presence, temperature, and/or pressure sensing at the junction between the distal end  14  and inlet port  11 . 
       FIGS. 5A and 5B  illustrate disposition of a sensor in, at, on, or near the distal end  14 . In this case, the first circuit element  55  may comprise a magnetic piece, a spring-loaded activator for a mechanical switch, or spring-loaded conductive strip. At the distal end  14 , the second circuit element includes a terminal element  57   a  and a sensor element  57   c . The terminal element  57   a  operates cooperatively with the first circuit element  55  to complete an electrical circuit allowing the sensor  57   c  to operate in the junction between the distal end  14  and inlet port  11 . In this case, the contact element  57   a  may comprise a reed switch, a Hall effect device, a mechanical switch, or two conductive posts, while the sensor element  57   c  may comprise a thermocouple or an air velocity sensor. As with the example illustrated in  FIGS. 4A and 4B , the examples of  FIGS. 5A and 5B  may incorporate more than one sensor at or near the distal end  14  and may sense presence, temperature and/or velocity. Furthermore, optical elements exist that could be incorporated to provide an analog of the electrical circuit shown in  FIGS. 5A and 5B . 
       FIGS. 5C and 5D  continue the illustration presented in  FIGS. 5A and 5B .  FIG. 5C  shows the planar member  50  engaged with the hose cord  30  thereby to join, couple, or mate the distal end  14  with the inlet port  11 .  FIG. 5D  is a side sectional elevation view taken along lines D—D in  FIG. 5C . In  FIG. 5D , the air hose  12 , has a conventional construction that includes a flexible side wall  12   s . In addition, the conductors  58   a  and  58   b  are embedded in, formed in, or attached to the side wall  12   s . The air hose  12  terminates at the distal end  14  in a cup-shaped plastic member  14   a  having a disk-shaped opening  14   o . The rim of the plastic member  14   a  is attached to the planar member  50 . The planar member  50  includes a first plate  50   p , preferably a plastic piece to which the rim of the plastic member  14   a  is bonded or joined. Another plastic piece  50   pp  is attached to the plastic piece  50   p ; this piece  50   pp  includes the extending side wall  52  and the lip  53 . The pieces  50   p  and  50   pp  are joined or otherwise bonded together to form the planar member  50  as a single, unitary piece. The thermocouple  57   c  is held between the two pieces  50   p  and  50   pp  and includes a portion that extends across an opening  50   o  provided through the planar member  50 . The hose card  30  includes two planar pieces  30   p  and  30   pp  that are glued or bonded together. An opening  30   o  in communication with the inlet port  11  aligns with the openings  50   o  and  14   o  so that an air flow path extends through the air hose  12  and the openings  14   o ,  500  and  30   o . One contact  57   a  is fixed in the planar member  50  at a location where it is contacted by the shorting bar  55  when the planar member  50  is seated on the hose card  30  as shown in  FIGS. 5C and 5D . 
       FIGS. 6A and 6B  illustrate an alternative embodiment of a presence sensor in which the opening in the center of the hose card  30  includes an edge  30   e  on and adjacent to which a conductive material  55   m  is disposed. The distal end  14  of the air hose  12  is configured as a nozzle  14   n  having a circumferential groove  14   g  in which two strips of conductive material  57   s  are disposed. Each of the strips  57   s  is connected to a respective one of the conductors  58   a  and  58   b  so that when the nozzle  14   n  is inserted into the hole in the hose card  30 , the groove  14   g  seats on the edge  30   e  and the material  55   m  completes or closes an electrically conductive pathway between the strips  57   s.    
     Yet another implementation of the presence sensor is illustrated in  FIG. 7  wherein the distal end  14  of the air hose  12  includes the nozzle  14   n  which transitions to a collar  14   c  within which a coil  57   i  is embedded. The coil  57   i  is connected to and driven by the conductors  58   a  and  58   b . Disconnected from the hose card  30 , the coil  57   i  exhibits an impedance having an electromagnetic characteristic (impedence, with an inductive component). A second coil  55   i  is embedded in the hose card  30   e  around the edge  30   e . Now, when the distal end  14  of the air hose  12  is seated in the hose card so that the collar  14   c  is adjacent the edge  30   e , the impedance driven by the conductors  58   a  and  58   b  has a value measurably different from that exhibited by the coil  57   i  when the distal end  14  is not seated in the hose card  30 . Alternatively, the coils  57   i  and  55   i  could be replaced with insulated conductive elements that exhibit a measurable capacitance whose value changes when the distal end  14  and the inlet port  11  are connected and disconnected. 
     One way in which to measure a change in an electromagnetic characteristic at the junction between the distal end  14  and the inlet port  11  would be to drive the circuit  58   a ,  57   i , 58   b  with a signal of known frequency generated by the control unit  21 . A change in the characteristic would be manifested by a change in frequency of the signal. 
     Another way in which to measure a change in an electromagnetic characteristic at the junction between the distal end  14  and the inlet port  11  would be to drive the circuit  58   a ,  57   i , 58   b  with a variable frequency signal that includes a known frequency generated by the control unit  21 . A change in the characteristic would be manifested by a change in the impedance of the circuit at the known frequency of the signal. 
     Yet another implementation of the presence sensor is to imbed a small piece of magnetic material in the hose card. This material may be excited with a single pulse from circuit  58   a ,  57 I,  58   b . The activation of the magnetic material would then cause resonance in that material with a back scattering of a characteristic frequency. This frequency would then be sensed through the same activating circuit of  58   a ,  57 I,  58   b.    
       FIGS. 8A and 8B  illustrate how a connection is made to the heater/blower unit  18  at the proximal end of  15  of the air hose  12 , to provide continuity of a signal pathway to the control unit  21  (not shown). In this regard, a connector plug  44   p  is mounted on a proximal end nozzle  15   n . The conductors  58   a  and  58   b  terminate on respective pins of the plug  44   p . When the nozzle  15   n  is received in the port  19  of the unit  18 , the pins of the plug  44   p  are received in respective receptacles of a connector socket  44   s  mounted on the unit  18 , adjacent to the port  19 , in alignment with the pins of the plug  14   p . As shown in  FIG. 8B , when the plug  44   p  and socket  44   s  are mated, the indicator  46  provides (in this example) a visual indication of joinder, mating, coupling, or connection between the distal end  14  of the air hose  12  and one of one or more inlet ports of an inflatable thermal device. 
       FIGS. 9 ,  10 A and  10 B illustrate inlet ports having sleeve-like constructions. Referring to  FIG. 9 , the distal end  14  of the air hose  12  has the nozzle  14   n  in which a slot  14   s  is cut. An edge  14   e  of the slot is exposed and elements of conductive material  57   m  are placed on the edge  14   e , in opposition across the slot  14   s . The inlet port  11  is embodied in a sleeve  70  of material that extends from and opens into an inflatable thermal device (not shown). An alignment and contact mechanism  72  is mounted on the inside of the sleeve  70  by appropriate means including, for example, gluing between the inside surface of the sleeve and the upper surface  72   u  of the alignment mechanism  72 . The alignment mechanism  72  may be a molded plastic piece that generally has the shape of the slot  14   s  and includes a peripheral slot-like recess  72   s  that receives the edge  14   e  of the slot  14   s . A strip of conductive material  55   m  is disposed in the alignment mechanism  72 , protruding in the opposed places into the peripheral slot-like recess  72   s . When the slot  14   s  is seated on the alignment mechanism  72 , an electrical circuit is completed or closed between the conductive material elements  57   m  by way of the strip of conductive material  55   m . In  FIGS. 10A and 10B , the end of the sleeve  70  has an elastic material integrated into the material of the sleeve  70  to form an elastic portion  70   e . On the inside surface of the elastic portion  70   e  a ring of conductive material  55   m  is attached. The distal end  14  of the air hose  12  has substantially the same construction as that illustrated in  FIGS. 6A and 6B , with the exception that the circumferential groove  14   g  is omitted. To join, couple, the distal end  14  in the inlet port  11  via the sleeve  70 , the elastic region  70   e  is expanded, and the distal end  14  is slid into the sleeve  70  until the collar  14   c  is in the portion of the elastic region  70   e  that is girded on its inside surface by the ring of conductive material  55   m , which closes or otherwise completes an electrical pathway between the conductive elements  57   s . The nozzle  14   n  is retained in the sleeve  70  by the grip of the elastic region  70   e  on the nozzle&#39;s outside surface. 
       FIGS. 11A through 11C  illustrate the inflatable thermal device where the inlet port  100  includes a hose card  102 . It should be understood that the inlet port  100  and hose card  102  are typically a component of an inflatable thermal device which is not shown as an effort to simplify the drawings. The hose card  102  is used to provide the first circuit element electrical connection and to provide mechanical stability to the air hose/inlet port interface. As shown in  FIGS. 6A ,  6 B,  7 ,  10 A, and  10 B, the first circuit element  104  is annular, surrounding the inlet port  100 . This permits the first, or distal end  106  of air hose  108  to freely rotate in the inlet port  100  without a loss of electrical continuity. The first hose end also includes the second circuit element, two electrical contacts  110   a  and  110   b  are shown, but in some aspects the second circuit element is a single electrical contact. The second circuit element  110   a / 110   b  cooperates with the first circuit element to enable a signal representing a connection between the first end  106  of the air hose  108  and the inlet port  100 . As mentioned above, the connection is made independent of the rotational alignment of the air hose in the inlet port. The rotational alignment is represented by reference designator  112 . In a simple aspect, the first  104  and second  110   a / 110   b  circuit elements are electrical contacts, the joining of which completes an electrical circuit, signifying that the air hose  108  is properly mated in the inlet port  100 . As is explained in more detail below, that connection of first  104  and second  110   a / 110   b  circuit elements can be used to conduct signals with information content which permit a more complex determination of the condition of the air hose  108  in the inlet port  100 . 
     In one aspect, as shown, the first circuit is made up of a plurality of members, such as member  114 , which have a saw-tooth shape ending in a peak pointing toward the center of the inlet port  100 . Typically, the hose card is made of cardboard, or some similarly pliable material so that as the air hose first end  106  is inserted in the inlet port  100 , the members  114  are deformed. Due to the tooth shape of the members  114 , which increases in thickness in moving towards the base of the tooth, the members gradually stiffen as the first hose end  106  is inserted. 
       FIG. 11B  illustrates the hose card  102  of  FIG. 11A  with a mated hose  108 . It is well known for the diameter of a hose to gradually increase in travel from the end for the purpose of making a snug connection with a mating port. One advantage of such a connection is the elimination of intermittent connection events which would be a nuisance for operators. Another advantage is in ensuring a reliable electrical connection, or a consistent value of resistance generated between deforming members  114  and second circuit elements  110   a  and  110   b.    
       FIG. 11C  is a cross-sectional view of the air hose  108  of  FIG. 11B  illustrating a modification to better receive the deformable members  114 . An annular groove  116  is formed in the first hose end around the outside diameter. The second circuit element  110   a  is seated the groove  116 . As the air hose  108  is inserted into the inlet port  110 , the members  114  are bent. The mechanical, and therefore electrical, connection between the first circuit element  104  and the second circuit element  110   a  is captured by the action of the stiffened members  114 , as well as by the bent shape of the members  114 . 
     To complete the electrical connection required for the first  104  and second  110   a / 110   b  circuit elements to cooperate, the first circuit element deformable members  114  have a surface coated with a conductive ink. The ink can include conductive elements such as copper, silver, and carbon, but is not limited to the use of just the named connective elements. One conductive ink found to be effective is manufactured by Acheson, under the part number of SS 24600. The conductive ink can be formulated to have a known resistance, permitting the controller to differentiate between different types of thermal devices. For example, it may be desirable to have the controller operate the blower under a first set of temperature and airflow parameters when a first kind of inflatable thermal device, having a first resistance measurement, is connected to the air hose. The control circuit is able to measure and recognize different resistance values, correlate these resistance measurements to corresponding inflatable thermal devices, and modify the temperature and airflow parameters in response to the measured resistance, so that a variety of inflatable thermal device can be operated at predetermined parameters from a single blower unit. 
       FIGS. 12A through 12C  illustrate an alternate aspect of the air hose  108  of  FIG. 11A  or the air hose  12  of  FIGS. 6A ,  6 B,  7 ,  10 A, and  10 B. That is, the second circuit element to be described can be used with a variety of first circuit element designs, including the hose card first circuit element. The air hose first end  106  is manufactured from a partially resistive material, such as a conductive polymer, in which electrical conductivity can be varied by loading the material with conductants such as carbon. These materials have a surface conductivity in-between standard plastics and metal. Conductive polymers are lighter than metal, and less subject to denting. The PermaStat® family of products manufactured by the RTP company is an example of such a material. The second circuit element is formed from a highly conductive element, such as metallic wire which is embedded in the polymer material. Two conductive elements  120   a  and  120   b  are shown. Electrical current can pass from the polymer nozzle surface to the embedded wires  120   a / 120   b , with the electrical resistance being at a minimum at the surface area immediately overlying the wires. That is, the second circuit element includes the conductive elements  120   a / 120   b  and the polymer surface overlying the elements. Further, the first circuit element  104  and second circuit element  110   a / 110   b  cooperate to enable a signal between the first circuit element (however defined) and the polymer hose surface immediately overlying the highly conductive element  120   a / 120   b . In other aspects, the polymer surface overlying the conductive elements  120   a / 120   b  is formed in a separate fabrication process from the deposition of the conductive elements and/or the formation of supporting layer of nozzle material that need not be the highly resistive polymer. 
     Regardless of whether the first circuit element is a simple electrical contact, a contact as described in the explanation of  FIGS. 6A ,  6 B,  7 ,  10 A, and  10 B, or the hose card design described in the explanation of  FIGS. 11A–11C , the impedance, resistivity, or conductance across the element can be measured and defined as a first impedance. Likewise, regardless of whether the second circuit element is as described in  FIGS. 6A ,  6 B,  7 ,  10 A,  10 B,  11 A–C, or  12 A–C, the impedance can be measured and defined as the second impedance. Then, the cooperation of the first  104  and second  110   a / 110   b  circuit elements provides an impedance which represents a connection between the first end of the hose and the inlet port. That is, the combination of impedances represents a condition where the air hose  108  is properly connected to the inlet port  100 . Too small an impedance could represent an improper connection or a short. Too large an impedance typically represents a disconnection in the cable connecting the sensor to the controller circuitry, such as the air hose  108  being improperly mated to inlet port  100 . In some aspects, the first impedance may be significantly larger than the second impedance, so that in measuring the series line impedance of a properly mated air hose  108 , the contribution of the second impedance to the measurement is of no consequence. In other aspects, the second impedance is significantly larger than the first impedance. 
     The impedance across the conductive ink first circuit element  104  of hose card  102  ( FIGS. 11A–11C ) is modified by the amount of conductant material in the ink, the conductive path, the ink thickness, or the stiffness of the members  114  when seated against air hose first end  106 . Likewise, the conductivity of second circuit element  110   a / 110   b  of  FIGS. 12A–12C  is modified by how far the conductive elements  120   a / 120   b  are buried in the polymer and the specific conductivity of the polymer material. 
     In other aspects (not shown), the air hose has a shape to encourage a particular alignment. That is, the air hose must be rotated to specific position to insert the air hose into the inlet port. In these circumstances the first circuit element no longer need be annular in shape. Further, since the position of the second circuit element contacts are predetermined, the first circuit element can be shaped to bridge the gap between the second circuit element contacts. 
       FIGS. 13A and 13B  illustrate an convective warming system using an electronic identification tag  130 . The electronic tag  130  provides information. In its simplest form, the tag  130  provides a single bit of information that is used to communicate that an electrical connection has been made. This aspect is similar in concept to the impedance measurement method described above in the explanation of  FIGS. 12A–12C . In other aspects the electronic tag  130  provides more information, which in turn, permits a wider range of responses. 
     Communication with the electronic identification tag  130  can be made through a direct-wired-connection, through a modulated magnetically radiated signal, and a modulated electrically radiated signal. When a direct electrical connection is to be made, any of the above-described methods to interface the first  104  and second  110  circuit elements can be used. However, when radiated signals are to be used, the first  104  and second  110  circuit elements must be radiating elements, or antennas, as shown. Interrogation and identification signals are coupled between radiating elements  104  and  110 . When radiated signals are used the electronic identification tags are often called radio frequency identifiers (RF IDs). The higher frequency electric fields can generally be propagated a further distance than the magnetic fields, given the same amount of transmit energy. It may be desirable to limit interrogations from the second circuit element  110 , so that the air hose does not communicate with neighboring inflatable thermal devices outfitted with RF IDs. 
     The first circuit element  104  at an inlet port of the inflatable device is connected to the electronic identification tag  130  to identify the inflatable device. The second circuit element  110  near the first end  106  of an air hose  108  is receivable in the inlet port  100 . The second circuit element  110  cooperates with the first circuit element  104  to enable an identification signal. As mentioned above, the identification signal may just represent a connection between the air hose first end  106  and the inlet port  100 . In these circumstances the electronic identification tag provides a 1-bit identification message. 
     Alternately, the identification can contain more information bits. At present, electronic identification tags which provide a 64-bit identification code are common, but are not limited to any particular message length. Among other things, the multiple-bit message can provide information which describes the inflatable thermal device model number, the inflatable thermal device serial number, the preferred air flow rate, the preferred air temperature, and patient identification. The air flow, temperature, and other parameters can be regulated in response to knowing this information. For example, the preferred air flow characteristics may differ for different inflatable thermal device models. Alternately, the tag  130  can be loaded to provide the patients identity, the number of times the blanket has been connected to the warming unit, and the amount of time the blanket has been in use. The air flow controlling mechanism can regulate air flow in response to local database of patient characteristics, or the air flow can be established in communication between the air flow controller and a central system. In other aspects, the electronic tag is worn by the patient. In some aspects the electronic tag supplies updated patient vital statistics which are downloaded through the air flow controller to a local file, or communicated to the central system. 
     The electronic tag must be powered to transmit a signal. The power can be maintained at the inflatable thermal device. That is, the first circuit element  104  includes a power supply (not shown) directly connected to the electronic identification tag  130 . Alternately, the second circuit is directly connected to the power source. Through coupling between radiating elements  104  and  110 , the second circuit element  110  cooperates with the first circuit element  104  to power the electronic identification tag  130 . 
       FIGS. 14A ,  14 B,  15 A– 15 C,  16 A, and  16 B illustrate some examples of mechanical solutions to the problem of controlling air flow to an inflatable thermal device according to the invention. These solutions rely on the act of coupling the air hose into the inlet port to open a valve and permit the flow of air. Likewise, the decoupling of the air hose from the inlet port causes the valve to close, preventing burn accidents or improper operation of the equipment. These solution do not rely upon the engagement of electrical contacts, the relaying of electrical signals, or electronic identification for the system to convectively control the temperature of an inflatable thermal device. 
       FIG. 14A  depicts an inflatable device inlet port  100 . The first end  106  of the mating air hose  108  includes a valve  130 . As seen in  FIG. 14B , as first end  106  of air hose  108  is received in the inlet port  100 , the valve  130  cooperating with the inlet port to enable airflow between the hose first end  106  and the inlet port  100 . Also, while  FIG. 14B  depicts the valve flap  136  opening toward the inlet port  100  upon activation, it is also possible to design a valve system in which the flap  136  opens towards the hose  108  upon activation. It should also be noted that the valve is engaged independent of the rotational alignment  132  of the air hose  108  in the inlet port  100 . That is, there is no single, or keyed position in which the valve operates. 
     The valve  130  includes two primary components, a flap  134  which has a diameter  136  substantially the same as the inner diameter of the air hose first end  106 , or at least the air hose diameter that interfaces with the flap. It should be noted that the flap  134  need not perfectly seal the air hose  108  to be effective. The flap  134  blocks the flow of air, or substantially blocks the flow of air, when the air hose  108  is not received in the inlet port  100 . The other main component of the valve  130  is the actuating mechanism, of which three examples are shown. 
     As depicted in  FIGS. 14A and 14B , in one aspect of the invention the valve  130  includes a hinge lever  138  which is rigidly attached to the flap. At the intersection of the hinge lever  138  and flap  134  is an axle or pin (not shown) about which the flap  134  and hinge level  138  pivot. The hinge lever  138  cooperates with the inlet port  100 , moving from a position perpendicular to the air hose  108 , to a position against the air hose  108 , to permit the hose first end  106  to fit inside the inlet port  100 . The engagement of the hinge lever  138  prevents the flap  134  from blocking the flow of air when the air hose first end  106  is received in the inlet port  100 . Not specifically shown is the mechanism which returns the flap  134  to the blocking position ( FIG. 14A ) when the air hose  108  is not engaged in the inlet port  100 . The return-mechanism can be a spring or some such torsioning member (not shown) which is put under load by the action of the flap being forced into the open position ( FIG. 14B ). Additionally, in some orientations, the valve flap can be returned to its seated position by the frictional force of the airflow within the air hose  108 . Once the valve flap  136  is seated, it will be held in place by the static pressure developed by the blower. 
     In some aspects of the invention a pair of magnets  139   a  and  139   b  are used to keep the flap  134  in the blocking position when the air hose  108  is not received in the inlet port  100 . The air hose  108  includes the first magnet  139   a , and the valve flap  134  includes the second magnet  139   b . The first magnet  139   a  cooperates with the second magnet  139   b  so that the flap  134  blocks the flow of air when the air hose  108  is not received in the inlet port  100 . Although not specifically shown, magnets can also be used with the flap  134  of the actuator mechanisms shown in  FIG. 15A , described below. In another aspect of the invention, not shown, the flap  134  is opened in the direction of the air hose  108  instead of the inlet port  100 , so that the flow of air through hose  108  acts to close the flap  134  when it is not engaged. 
       FIGS. 15A through 15C  depict the valve flap  134  of  FIG. 14A , with a cam actuation mechanism. As shown in  FIG. 15A , the flap  134  includes a pair of cams  140   a  and  140   b  rigidly attached to the flap  134 , 180 degrees apart. Alternately, the cam can be attached to an axle running through the diameter of the flap  134 , with the axle being rigidly attached to the flap, so that the face of the flap and the cam facets remain in a fixed relationship. The cam includes rounded surfaces which permit the cams  140   a / 140   b , and attached flap  134 , to rotate as the cam engages the surface surrounding the inlet port  100 . The rotation of the cams  140   a / 140   b  is shown if  FIG. 15B . As shown in  FIG. 15C , the flat facet surfaces of the cams  140   a / 140   b  permit those surfaces to fixedly seat against the inlet port as the air hose  108  is engaged. With the cams  140   a / 140   b  seated, the flap  134  is locked in an open position to permit the flow of air. Not shown is the return mechanism which forces the flap  134  into the blocking position ( FIG. 15A ). As above, the return mechanism can be a spring, or the like that is put under load as the flap is forced into the open (non-blocking) position. 
       FIGS. 16A and 16B  depict the gear rack valve actuator mechanism. The mechanism includes a lever  150  which engages the inlet port to open the flap  134 . Lever  150  is connected to a first gear  152 , the teeth of which are intermeshed with the teeth of a second gear  154 . In turn, the second gear  154  is attached to flap  134 . As the lever is engaged, it is forced into the body of the hose  108 . The action of the lever  150  and the gears  152 / 154  open the flap  134  so that air can pass through the hose  108  into inlet port  100 . In some aspects of the invention a pair of magnets  139   a / 139   b  are used to keep the flap  134  in the blocking position when the air hose  108  is not received in the inlet port  100 . In other aspects, the opening of the flap  134  into the direction of the airflow acts to force the flap  134  into a blocking position when level  150  is not engaged in inlet port  100 . 
       FIG. 17  is a flowchart illustrating a method for controlling air flow in a system including an inflatable thermal device, corresponding to  FIGS. 14A–14B ,  15 A– 15 C, and  16 A– 16 B. Step  400  includes the inflatable thermal device having at least one inlet port, at least one surface adapted to expel air, and an air hose having two ends and a valve to prevent the delivery of a flow of pressurized air to the inflatable thermal device. Step  402  inserts an end of the air hose into the inlet port of the inflatable thermal device. Step  404 , in response to inserting the air hose into the inlet port, opens the valve. The opening of the valve in Step  404  includes the valve cooperating with the inlet port. Step  406  is a product where the inflatable thermal device is operated by conducting a flow of pressurized air through the air hose. 
     Step  400  includes a valve having a flap with a diameter that is substantially the same as the air hose first end diameter. The method further comprises Step  408 . Step  408  blocks the flow of air with the valve flap when the air hose is not received in the inlet port. 
     In some aspects of the invention Step  400  includes a valve with a hinge lever. Then, the opening of the valve in Step  404  includes the hinge lever cooperating with the inlet port to prevent the flap from blocking the flow of air when the air hose is received in the inlet port. 
     In some aspects of the invention Step  400  includes a valve with seating cams. Then, the opening of the valve in Step  404  includes the seating cams cooperating with the inlet port acting to prevent the flap from blocking the flow of air when the air hose is received in the inlet port. 
     In other aspects, Step  400  includes an air hose with a first magnet and a valve flap includes a second magnet. Then, the blocking of the air flow in Step  408  includes the first magnet cooperating with the second magnet, positioning the flap to prevent the flow of air when the air hose is not received in the inlet port. 
     In some aspects of the invention Step  402  includes making an electrical connection when the air hose end is inserted into the inlet port. As described in detail above, the electrical connection can be an on/off determination, an impedance measurement, or inflatable thermal device identification. Then, Step  406  includes operating the inflatable device by delivering the pressurized air in accordance with parameters that are responsive to the electrical connection made. For example, the inflatable device could be supplied with no air, or less heat, if an electrical connection is not made, regardless of whether the flap is open. Otherwise, the parameters of the airflow such as rate and temperature can be varied in responsive to an impedance measurement, or digital identification of the inflatable thermal device. 
     Clearly, other embodiments and modifications of the present invention will occur readily to those of ordinary skill in the art in view of these teachings. For example, inflatable thermal devices may have more than one inlet port. Also, a heater/blower unit with more than one air hose may fall within the scope of this invention. Further, the invention may be applied to convective systems having the elements of  FIG. 1  that cool persons, animals, or things. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications.