Abstract:
A warming system, mounted to the foot of a bed, warms a person&#39;s lower extremities by directing air into the space between the mattress and overlaying blankets. A blower directs air into an elongated distribution chamber having many tiny exit apertures. The chamber is mounted at the foot of the bed, so that air exiting the apertures warms the person&#39;s feet. For maximum thermal transfer, the chamber is placed under the sheet and any blankets, but above the mattress cover and fitted sheet. The chamber may be implemented by a length of open cell foam, a hollow manifold with many punctures or other tiny distribution apertures, collapsible pocket, etc. While the person is lying on the bed beneath the blankets, with feet proximate the foot of the bed, the blower directs temperature-regulated air into the chamber and through the exit apertures, thereby warming the person&#39;s feet. A temperature regulator ensures a normothermic air temperature (or alternatively, hyperthermic air temperature.) Thus, the invention helps relieve or prevent “cold feet” by directing normothermic air at a person&#39;s lower extremities. Additionally, by applying heat to the feet and legs, the invention encourages blood flow by virtue of sympathetic vasodilation and local temperature-mediated vasodilation. The invention is also believed to prevent some leg and foot ulcers from forming by maintaining the lower extremity at a near normal temperature during sleep.

Description:
This is a continuation of U.S. patent application Ser. No. 09/439,548, filed on 12 Nov. 1999, now U.S. Pat. No. 6,473,920. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns external techniques to warm the human body for comfort, therapy, surgery, or other treatment. More particularly, the invention concerns a warm air blower that is mounted to the foot of a bed and utilized to direct warm air to the lower extremities of a supine person. 
     2. Description of the Related Art 
     Many people complain of having “cold feet” while laying in bed. For some people, they simply feel colder at any given temperature than other people. For others, the problem is more serious because they suffer from inadequate circulation to the legs and feet, resulting in abnormally cold feet and legs. In either case, the perception of cold feet can cause significant discomfort, especially while trying to sleep. 
     Normal body core temperature (“normothermia”) occurs at about 37° Celsius. Body temperatures below this are considered “hypothermic,” and have many negative physiological effects beyond mere discomfort. Temperature excursions of a mere 1–2° Celsius below normal can profoundly affect many cellular and physiological functions in areas such as the immune system, coagulation system, cardiovascular system, and death rates during surgery. According to one published study, surgical patients with a core temperature of 34–35° Celsius experienced three times more wound infections than persons maintained at 36° Celsius. 
     Historically, the definition of “normothermia” has been limited to the core thermal compartment of the body. The peripheral thermal compartment, including the legs and other extremities, is designed to act as buffer or insulator between the core and the environment. Therefore, the peripheral compartment is expected to be hypothermic under many circumstances. This is one example of an “evolutionary tradeoff.” Namely, in order to maintain their core temperatures within a narrow range, warm blooded animals readily sacrifice warmness of the extremities. 
     This natural tendency toward peripheral hypothermia is exacerbated by vascular disease, which further reduces blood flow to the extremities. In fact, the combination of sacrificial hypothermia of the extremities and peripheral vascular disease can result in especially profound hypothermia of the legs. Persons with vascular insufficiency of the legs generally have colder legs, sometimes even approaching room temperature. These same persons are also prone to chronic non-healing skin wounds on their legs. These wounds may originate for various reasons, such as diabetes causing small vessel disease, external pressure causing local vascular occlusion, venous disease, and circulatory insufficiency reducing the blood flow and changing the hydrostatic gradients. 
     Whether peripheral hypothermia results from vascular disease, sacrificial hypothermia, or both, this condition inhibits important cellular functions of leg tissue. These cellular functions are not any different, or less important, than functions of cells in core vital organs. For example, a circulating immune cell does not know if it is fighting an infection in the heart or lungs, or the big toe. However, the extremities are more often hypothermic than the core vital organs, and therefore suffer more frequently from hypothermia-induced limitations. 
     Hypothermia in the lower extremities, then, is especially prevalent due to sacrificial hypothermia, peripheral vascular disease, or a combination of both. Peripheral hypothermia causes pain and possible interference with cellular functions of leg tissues. 
     SUMMARY OF THE INVENTION 
     Broadly, the present invention concerns a warming system, mounted to the foot of a bed, to warm a person&#39;s lower extremities by directing air into the space between the mattress and overlaying blankets. The system utilizes a blower to direct air into an elongated, air permeable, fluid distribution chamber. The chamber is mounted at the foot of the bed, and spans the bed from side to side so that air exiting the chamber warms the person&#39;s feet. For maximum thermal transfer, the chamber is placed beneath blankets and other layers that cover the person, but above any lower layers such as a mattress cover and fitted sheet. Various embodiments of the chamber are contemplated, such as a length of open cell foam, a hollow manifold that is naturally air permeable, air impermeable hollow manifold with many punctures or other tiny distribution apertures, collapsible tube, etc. While the person is lying in bed beneath the blankets, with feet proximate the foot of the bed, the blower directs temperature-regulated air into the chamber; when the air exits the chamber, it warms the person&#39;s feet. Temperature is regulated to provide an infusion of warmed air. 
     As discussed above, one embodiment of the invention may be implemented to provide an apparatus to manage temperature in a supine person&#39;s legs and feet. A different embodiment concerns a method to manage temperature in a person&#39;s lower extremities. 
     The invention affords its users with a number of distinct advantages. For example, the invention relieves or even prevents the discomfort of “cold feet” by directing normothermic air at a person&#39;s peripherally hypothermic lower extremities. Additionally, by applying heat to the legs, the invention encourages blood flow to the legs by virtue of sympathetic vasodilation and local temperature-mediated vasodilation. The invention is also believed to prevent some leg and foot ulcers from forming by maintaining the lower extremities at a near normal temperature during sleep. 
     Moreover, by warming the feet and legs during the sleep hours, the present invention is believed to help provide improved healing of chronic ulcers of the leg or foot that have resulted from vascular insufficiency of the legs. Recent experiments have shown promise for healing chronic wounds by warming them from a typically hypothermic state toward normothermia. Warming the wound toward a normothermic temperature helps enable normal cellular functions that are inhibited by hypothermia. As proposed by the present inventors, severely hypothermic wounds are believed to exist in a state of “suspended animation,” where the cells are alive but inactive. Severe hypothermia causes cell division (“mitosis”) to stop, enzyme and biochemical reactions to be slowed or stopped, cell membrane functions to be altered, and the immune system to be inhibited. The result is that wounds are slow to heal, if ever. Thus, by gently warming the peripheral extremities, the present invention contributes to the healing of chronic wounds that would otherwise linger due to hypothermic interference. 
     In contrast to other arrangements such as heating blankets, the invention focuses heated air primarily on persons&#39; feet and lower legs. As the face and torso are sensitive to temperature, many people do not tolerate additional heat applied to the body during sleep. In fact, some people might turn a heating blanket off because they feel too warm, yet their legs and feet are still hypothernic. In contrast, people tolerate more heat applied to the legs than the body and face before complaining of feeling too warm. People with diabetes and vascular disease are even more heat tolerant, because they tend to lose sensation in their feet and legs. The present invention capitalizes upon these facts by focusing heat upon the lower extremities. 
     As another benefit, in the case of people with vascular disease, diabetes, or another condition causing poor circulation in the peripheral extremities, the invention preferably regulates the temperature of warming air to about 38° Celsius. This temperature is normothermic since it approximately coincides with the upper limit of the body&#39;s normal core temperature. The approach of this invention diverges from electric blankets and other known heating devices, which typically apply a hyperthermic temperature to a person in order to develop a temperature gradient. By using a normothermic temperature, the invention helps avoid thermal injuries such as burns, which can occur without a person&#39;s knowledge because of the reduced sensory perception in the peripheral extremities. By limiting the temperature of warming air to about 38° Celsius, the invention can still induce a sufficient temperature gradient to induce warming because a peripherally hypothermic person&#39;s feet and legs are colder than normal. While approximately 38° Celsius is the preferred air temperature, it should be noted that temperatures higher and lower than 38° Celsius are also contemplated. The invention also provides a number of other advantages and benefits, which should be apparent from the following description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the hardware components and interconnections of one exemplary implementation of the invention. 
         FIG. 2  is a perspective view of a adjustable length air distribution chamber according to the invention. 
         FIG. 3  is a perspective view of an inherently porous air distribution chamber according to the invention. 
         FIG. 4  is a perspective, partially cutaway view of a collapsible air distribution chamber with a helical support structure according to the invention. 
         FIGS. 5–10  are cross-sectional side views showing various embodiments of mounting hardware to position the air distribution chamber according to the invention. 
         FIG. 11  is a flowchart of an operational sequence for warming the lower extremities of a supine person according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The nature, objectives, and advantages of the invention will become more apparent to those skilled in the art after considering the following detailed description in connection with the accompanying drawings. 
     HARDWARE COMPONENTS &amp; INTERCONNECTIONS 
     Introduction 
     As mentioned above, the invention concerns a warming system, mounted to the foot of a bed, to warm a person&#39;s lower extremities by directing air or another warm gas into the space between the mattress and overlaying blankets. Although many different hardware components and configurations may be used,  FIG. 1  shows one example embodied by the system  100 . 
     A person  102  is shown in supine position on a bed  104  that has a head end  104   a  and foot end  104   b . The person is covered by one or more blankets  106 . The system  100  employs a blower  110  to direct air into an elongated distribution chamber  108 . The chamber  108  includes many tiny exit apertures  109 . In one embodiment, the chamber  108  may comprise an otherwise air impermeable material, with many tiny apertures  109  defined therein. In another embodiment, the chamber  108  may comprise an air permeable substance such as a woven fabric, mesh, flexible lattice, fibrous structure, etc. The air permeable substance naturally defines many tiny apertures  109 ; additional apertures may be created to enhance air flow if desired. 
     The air is conditioned by a temperature regulator  113 . The blower  110  and chamber  108  are coupled by a supply hose  111 . The chamber  109  is mounted at the foot end  104   b , so that air exiting the apertures  109  warms the person&#39;s feet  103 . For maximum thermal transfer, the chamber  108  is placed under the blankets  106 , but above any mattress cover, fitted sheet, and lower bedding. For ease of explanation, “upper sheet” is used to collectively refer to sheets, blankets, comforters, and other layers that cover the person. In contrast, “lower layers of bedding” refers to fitted sheets and other like materials that are placed about the mattress and therefore normally reside beneath a person in bed. 
     Bed 
     The invention may be implemented with nearly any sleeping arrangement. To provide some examples, the bed  104  may be a spring bed, air mattress, water bed, cot, hospital bed, cot, futon, or another sleeping surface. The mattress  105   a  may be supported by various structures, such as a box spring  105   b  (as illustrated), frame, floor, etc. 
     Air Distribution Chamber 
     The chamber  108  extends across some or all of the bed&#39;s width, and may be constructed in various fashions. In the embodiment of  FIG. 1 , the chamber  108  includes a length of tubular conduit, such as semi-rigid plastic, defining many apertures  109  that allow air to escape. As shown in  FIG. 2 , the chamber may comprise sections  200  of conduit that snap screw, plug, slide or otherwise join, permitting the user to adjust the conduit&#39;s overall length according to the bed size. In a different example ( FIG. 3 ), the chamber  108  comprises an air permeable material such as a length 300 of open cell foam, sponge, fibrous material, mesh, etc. The apertures in the chamber may be the natural spaces within the porous material, and/or additional channels, pores, or other openings may be created. 
     In still another embodiment ( FIG. 4 ), the chamber  108  may comprise a collapsible pocket  400  that inflates whenever it receives air from the blower  110 . This collapsible structure may comprise cloth, plastic, or another suitably pliable material. The pocket  400  may optionally include a semi-rigid helix  402 , lattice, or other internal supporting structure to maintain the chamber  108  in tubular form. The collapsible structure may include natural air permeability and/or apertures defined therein. 
     Mounting Hardware 
     During use, the air distribution chamber  108  is placed at the foot of the bed  104 . The chamber  108  may be used with or without being mounted. In most cases, however, the chamber  108  preferably secured by some mounting hardware, which is described as follows. The chamber may be positioned in many ways, with a suitably diverse selection of mounting hardware. The chamber may be located between the blankets and the lower layers of bedding, or it may be integral with the mattress, blanket or lower layers of bedding. 
       FIG. 5  shows one embodiment of mounting hardware, which utilizes a first member  500  of flat, relatively rigid material, such as a plastic sheet or bar. This member  500  is positioned between the vertical side of the foot end of the mattress and the blankets  106 . The blankets  106  are tucked under the mattress  105   a  and wrap around the first member  500  and chamber  108 , and then cover the person. This embodiment of mounting hardware also includes a second member  502  of flat, relatively rigid material, sandwiched between the bottom side of the foot end of the mattress  105   a  and the box springs  105   b  (or other structure beneath the mattress). As shown, the second member  502  is attached to the first member at substantially ninety degree angle, and helps secure the first member  500  and chamber  108  in position. 
       FIG. 6  shows a different embodiment of mounting hardware, which positions the chamber  108  using a first member  600  only. The second member  502  ( FIG. 5 ) is omitted. The first member  600  is held in place by the blankets  106 , which are firmly tucked in between the mattress  105   a  and box spring  105   b . Alternatively, the first member  600  may be held in place by other means, such as (1) slidable insertion into a vertical pocket sewn into the lower layer of bedding  602  at the foot of the bed, (2) slidable insertion into a vertical pocket sewn into the lowermost layer of blanket  106 , or (3) fasteners attaching the member  600  to the sheet or blankets. Some exemplary fasteners include hook and loop (e.g., VELCRO brand), snaps, clips, adhesive, etc. 
       FIG. 7  shows a different embodiment of mounting hardware. In this arrangement, the chamber  108  resides in a channel  700  defined in the mattress  105   a . The chamber  108  is held in place by the walls of the channel  700 . Additionally, the chamber  108  may be positioned beneath a lower layer of bedding  702 , further holding the chamber  108  in the channel  700 . 
       FIG. 8  shows a different embodiment of mounting hardware. In this setup, the mattress  105   a  does not include a channel  700  (as in  FIG. 7 ), but the chamber  108  is nonetheless held in position by virtue of being placed beneath the lower layer of bedding  800 . The chamber  108  may be further fixed in position by sewing the chamber  108  into the lower layer of bedding  800 , or a pocket sewed thereto. Alternatively, instead of using the lower layer of bedding  800 , the chamber  108  may be fixed in position by sewing the chamber into a layer of the blanket  106 , or a pocket sewed thereto. 
       FIG. 9  shows still another embodiment of mounting hardware. In this arrangement, the chamber  108  is secured to a support structure  902  that is secured to a lower layer of bedding  904 . The support structure  902  serves to keep the chamber  108  fixed in position, keep the chamber&#39;s apertures (e.g., apertures  109  in  FIG. 1 ) oriented correctly to blow air toward the patient&#39;s feet  103 , and keep the chamber  108  properly aligned with the bed. The support structure  902  may be implemented in many different ways, such as a molded plastic construction shaped to receive the chamber  108  and attached to the bedding  904  by hook and loop fasteners, fabric straps, adhesive strips, etc. Such a molded plastic construction may run along some or all of the chamber&#39;s length, and may even be implemented by several small brackets located at various points along the chamber&#39;s length. 
       FIG. 10  shows a different embodiment of mounting hardware. In this arrangement, there exists a specially configured structure toward the foot of the bed. This structure includes an air impermeable outer layer  1004  and an air permeable inner layer  1006 . The outer layer  1004  has an inlet  1005 , permitting air from the supply hose  111  to enter the spaces between the layers  1004 ,  1006  and inflate one or more air channels  1002 .  FIG. 10  shows two such inflatable channels  1002  in cross-sectional view. If desired, the channels  1002  may be collapsible whenever air does not flow from the supply hose  111 . Optionally, each channel  1002  may include an internal support member such as a helix of plastic or wire. 
     Since the inner layer  1006  is air permeable, air from the channel  1002  is exhausted through the layer  1006  into the space  1010  around the patient&#39;s feet  103 . In one embodiment, the inner layer  1006  may comprise an otherwise air impermeable material with air exit apertures therein. In another embodiment, the inner layer  1006  may comprise an air permeable material, such as a woven fabric, mesh, flexible lattice, fibrous structure, etc. 
     The layers  1004 ,  1006  may be sewn, attached, or otherwise incorporated into the blankets  106 . Alternatively, the layers  1004 ,  1006  themselves may provide a lower-body blanket that lies beneath the blankets  106  or between blanket layers, with or without connection to the blankets  106 . 
     Blower 
     As mentioned above, one component of the system  100  is a blower  110  ( FIG. 1 ). The blower  110  forces air into the air distribution chamber  108  via the supply hose  111 . Under pressure from the blower  110 , air passes through the apertures  109  and exits the chamber  108  into the space where the person&#39;s feet  103  reside between the blankets  106  and bed  104 . Air from the chamber  108  remains trapped in a space created by the person&#39;s feet between the mattress and the blankets, and thereby warms the person&#39;s feet during a period of extended contact. 
     When used with sensitive surgical or other hospital patients, the blower  110  should comprise a quiet unit. In an exemplary application, the blower may provide an output air flow between five and twenty-five cubic feet per minute. However, the airflow may vary widely from this range depending upon the specific design of the chamber  108 , apertures  109 , hose  111 , etc. 
     For ease of illustration, the present description depicts a blower  110  that withdraws air from the atmosphere and blows this air into the hose  111 . In certain applications, however, ambient air may be undesirable for health, hygiene, therapy, or other reasons. Under these circumstances, the blower  110  may withdraw air from a prescribed vessel, filter, or other non-ambient air source. Thus, the blower  110  may be operated to provide filtered air, a substance other than air, or a greater concentration of a gas normally present in air (e.g., oxygen), etc. Additionally, the blower  110  may mix different input gases, such as injecting medication into the blower&#39;s air stream, or even mixing two non-air substances. Furthermore, in some cases, non-gas fluids may be utilized in small amounts, e.g. adding water vapor to increase humidity, etc. 
     Temperature Regulator 
     As mentioned above, the system  100  also includes a temperature regulator  113 . The regulator  113  may be integrated into the blower  110 , or it may be separate. In an integrated embodiment, the blower/regulator may comprise a self-contained unit such as a space heater. Whether integrated with the blower  110  or not, the temperature regulator  113  may be configured to condition air before, during, or after the air is moved by the blower  110 . As one example, the regulator  113  may comprise an electrical resistance type heater. 
     The temperature regulator  113  may be implemented in many different ways. As one example, the regulator may comprise a digital data processing apparatus that operates by executing a sequence of machine-readable instructions. Examples of this embodiment include microprocessors, personal computers, computer workstations, and the like. One embodiment of regulator that is suitable for this implementation uses time-based temperature regulation. For example, the regulator  113  may be programmable to decrease or increase the air temperature after a selected period of time, turn the unit “on” or “off” at prescribed times, etc. 
     A different embodiment of the regulator  113  uses logic circuitry instead of computer-executed instructions to perform similar temperature control functions. Depending upon the particular requirements of the application in the areas of speed, expense, tooling costs, and the like, this logic may be implemented by constructing an application-specific integrated circuit (ASIC) having thousands of tiny integrated transistors. Such an ASIC may be implemented with CMOS, TTL, VLSI, or another suitable construction. Other alternatives include a digital signal processing chip (DSP), field programmable gate array (FPGA), programmable logic array (PLA), and the like. The regulator  113  may even use discrete circuitry, such as resistors, capacitors, diodes, inductors, transistors, and other components configured as a feedback loop or other circuit structure to automatically control temperature. 
     One specific example of the temperature controller  113  employs an electronic or electro mechanical temperature controller. For instance, the temperature controller may sense output air temperature and adjust the electrical current provided to the heater element to maintain an operator-specified output air temperature. As a different example, the regulator  113  may employ multiple heating elements that can be independently activated. For lower temperatures, a single element may be energized whereas for higher temperatures, multiple elements may be energized. In this case, the regulator  113  selectively activates the multiple heater elements using predetermined information such as a lookup table correlating various combinations of activated heater elements with empirically determined output temperatures likely to be produced under average room temperature conditions. 
     Depending upon the particular hardware used to construct the regulator  113 , an operator may use various means to select the desired temperature. For instance, an operator may select the desired temperature by programming the regulator  113  (which subsequently operates automatically), turning a dial, punching a keypad, adjusting a rheostat, sliding a lever, etc. 
     The temperature of the blower&#39;s output air is important for various reasons. As mentioned above, the present inventors recognize that persons with diabetes and other vascular diseases frequently lose sensation in their feet and legs. These people are prone to foot injuries because they cannot feel blisters and other injuries forming, and therefore fail to take any preventive action. Relatedly, these people are prone to burn injuries because they cannot feel the temperature and pain of thermal damage to the skin. Thermal damage to inadequately perfused skin can occur at temperatures as low as 40° Celsius. By most standards, 40° Celsius is merely warm, not hot, yet in the case of inadequate blood flow to the skin, this temperature can cause a thermal injury or burn. Therefore, for the foregoing reasons, it may be desirable for the temperature regulator  113  to warm the air around the person&#39;s feet to a temperature that is greater than room temperature and less than 40° Celsius. As a more specific example, the regulator  113  may warm air to a temperature corresponding the upper limit of normothermia, such as about 38° Celsius. Limiting air temperature to the upper limit of normothermia is especially desirable to avoid skin damage in people that have limited sensation in their lower extremities due to diabetes, vascular disease, or another condition affecting circulation. 
     OPERATION 
     In addition to the various hardware embodiments described above, a different aspect of the invention concerns a method to manage temperature in a person&#39;s lower extremities.  FIG. 11  shows a sequence  1100  to illustrate one example of this aspect of the invention. For ease of explanation, but without any intended limitation, the example of  FIG. 11  is described in the context of the system  100  described above. 
     The steps  1100  are initiated in step  1102 . In step  1104 , medical staff use mounting hardware as described above to affix the air distribution chamber  108  at the foot of the bed  104 . If desired, the chamber  108  may be laid at the foot of the bed without any attachment. Step  1104  also includes the additional steps of attaching the hose  111  to the chamber  108  and blower  110 , applying electrical power to the blower  110 , selecting the desired output temperature, entering any additional programming the blower  110  if applicable, etc. In step  1106 , the person  102  gets into bed. If desired, the order of steps  1104 ,  1106  may be reversed or even combined. 
     After step  1106 , with the person  102  and the warming system in place, steps  1108 ,  1110  are performed. In step  1108 , the temperature regulator  113  begins to regulate the temperature of the air or other air being supplied by the blower  110 . As discussed above, the regulator  113  provides output air temperature near the upper limit of normothermia, or about 37° Celsius. For people with normal pain sensation in the feet, the regulator  113  may even produce hyperthermic temperatures. Concurrently with step  1108 , the blower  110  starts to direct air (or other air) to the chamber  108  in step  1110 . Pressure from the blower  110  forces air out the apertures  109  in the chamber  108 . As the person  102  lies on the bed, the person&#39;s feet  103  protrude and create a space between the blanket  106  and bed  104 . Air emerging from the nearby apertures  109  warms this space between the blanket  106  and bed  104 , thereby surrounding the feet with warm air. 
     After steps  1108 ,  1110  start air flow and temperature regulation, step  1112  determines whether an operator has issued an “off” command, such as by turning off the regulator  113 , blower  110 , or a master control. If not, air flow and temperature regulation continue in step  1114 . Otherwise, when the “off” command is detected, the routine  1100  ends in step  1116 . 
     OTHER EMBODIMENTS 
     While the foregoing disclosure shows a number of illustrative embodiments of the invention, it wwill be apparent to those in the art that various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims. Furthermore, although elements of the invention may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.