Abstract:
An interactive enthalpy exchange system for infant care includes a pouch for receiving an infant, and a heat source arranged in the pouch. The heat source includes a first heat source and a second heat source different from the first heat source. Control circuitry is operatively coupled to the heat source, the control circuitry configured to control interactive enthalpy between the first heat source and the second heat source to maintain a temperature within the pouch at a prescribed temperature.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims priority of U.S. Provisional Application No. 62/288,480 filed on Jan. 29, 2016, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to an apparatus and method for providing warming therapy for newborn babies in remote areas and developing countries. More specifically, the invention relates to an interactive enthalpy exchange system between primary and secondary heat sources and the patient, all being ambient sensitive 
       BACKGROUND 
       [0003]    Roughly 15 million infants are born premature every year. Prematurity is a daunting challenge we face all over the world, despite advances in healthcare. Due to the lack of standardized healthcare infrastructure available for the pregnant mother and newborn infant, prematurity is more prevalent in rural areas and developing countries. With a disproportionately large body surface and little subcutaneous fat with respect to the total body weight, newborns, especially a majority of the low birth weight infants (LBW&lt;2.5 Kg) and very low birth weight infants (VLBW&lt;1.5 Kg), are at higher risk for hypothermia. Hypothermia is defined as the consequence when total heat loss exceeds an infant&#39;s ability to generate heat and maintain normothermia. 
         [0004]    According to the World Health Organization (WHO), a newborn with a temperature of 36.0-36.4° C. is under cold stress (mild hypothermia), which should give rise to concern; 32.0-35.9° C. is in danger and must be warmed right away (moderate hypothermia), and &lt;32° C. has a grave outlook with urgently required skilled care (severe hypothermia). Prolonged hypothermia is linked to impaired growth with increased neurological deficits, increased vulnerability to infections (e.g., sepsis), and negative effects on auto-immune functions, all leading to increasing infant morbidity and mortality rates in the world. Helping to maintain normothermia of a newborn infant&#39;s first few days of life is important to long-term sustenance and a reduction of morbidity rates overall. Fragile LBW and VLBW premature infants are susceptible to deleterious injuries, as a result of repeated handling and constant movement. It is best to maintain a stable, warm environment in the first few days of life until the infant is able to regulate its body temperature or until the infant is in the hands of trained caregivers in nearby dispensaries/hospitals, where standardized care can be accessed. 
         [0005]    Thermal stability is important for survival of premature LBW and VLBW newborn infants. Although body heat is lost in four ways (conduction, convection, radiation and evaporation), normothermia can be attained with external sources. Thermal stability can be achieved indirectly via forced air warming in incubators, directly via radiation with radiant warmers (e.g., remote heating with heat lamps etc.) and through a reduction in evaporation by wrapping the infant with a thermal insulator (e.g., plastic wrap etc.) to preserve humidity. Indirect and remote heating methodologies used in complex stationary/transport incubators and radiant warmers readily available in advanced countries require high power (up to 2 A at 240 VAC is roughly 480 watts 500 W) and are very expensive ($25,000-150,000). They are unfit for use in remote locations in developing countries as they require continuous power and rigorous cleaning. Due to the presence of airborne pathogens as a result of closed-loop warming, thorough disinfection with harsh industry chemical agents is essential for incubators, a lack of which can give rise to cross-contamination between patients. For these reasons, incubators are not accepted as a standard of care in most developing countries. Radiant warmers currently accepted are unsuitable for transport and cannot be used outside of the hospital setting. 
         [0006]    U.S. Pat. No. 7,934,537 B2, May 3, 2011 to Kolowich discloses the use of a thermally equalizing phase change material intended to first bring down a hot beverage temperature by heat absorption followed by releasing thermal energy back from the phase change material stacked between an inner and outer receptacle to the beverage to help maintain it in a warm state for an extended period. 
         [0007]    A transwarmer disclosed in U.S. Pat. No. 5,058,563, to Manker et al. discloses the use of an inorganic, salt-based warming gel to support infant transport and radiology exams for up to 2 hours. This is not economical and therefore unreasonable for maintaining normothermia in the first few days of life. 
         [0008]    U.S. Pat. No. 8,257,417 B2, Sep. 4, 2012 to Chen et al. takes this concept a bit further with the use of organic based phase change material mattress that can be used roughly 50 cycles for up to 4 hours per use. U.S. Pat. No. 8,834,548 B2, Sep. 16, 2014 to Liang et al. provides a suitcase shaped warmer for this phase change material mattress based on water heating or electric heating for reuse. This was followed by US patent application no. US2015/0066119 A1, Mar. 5, 2015 of Panicker et al. which discloses monitoring patient temperature with an electronic display with integrated visual alarms prompting user intervention. 
         [0009]    In general, every incubator/warmer manufacturer has some kind of monitoring equipment built-in to their device. The phase change material (PCM) works well when the temperature is elevated to above the solid-liquid transition temperature, however the PCM becomes very solid below this transition temperature as the material cools off rapidly. Hypothermia induced as a result of removing heat in the first few days of the fragile infant can be dangerous. Repeated handling to change the mattress every few hours can also be harmful to the infant. 
       SUMMARY OF THE INVENTION 
       [0010]    A practical, transportable, battery powered infant warming strategy that is adjustable to ambient surroundings is described. The device in accordance with the invention provides instant warmth to an infant and can be economically used in remote areas and in developing countries. 
         [0011]    The device in accordance with the invention highlights advancements with patient warming for a period of 1-2 days, while also obviating the need for repetitive handling of fragile infants. A primary heat source may be used with moderate to high latent heat capacity, capable of providing warmth for up to 4 hours that can be extended to a period of two days with an efficient, safe, secondary warming medium. Efficiency may be maintained by presenting the user a means of controlling secondary heat based on the patient temperature, embedded environment and ambient surroundings. 
         [0012]    The device in accordance with the invention can utilize an interactive enthalpy exchange system between primary and secondary sources including the patient, all being ambient sensitive, i.e., responsive to temperature changes of the primary material, secondary heat source, the patient, and environment during transport until the patient is transferred to a stable clinic or hospital environment. The secondary heat source can be composed of either a rigid or flexible printed circuit board-based resistive network that can be powered with a rechargeable, portable battery. 
         [0013]    High-efficiency conductive, gel-based heating (i.e., direct heat transfer via conduction) may be possible during infant transport with specialized mattresses. These one-time use mattresses maintain 40° C. on their surface where the infant is placed for a period of up to 2 hours. Repetitive use of up to 50 times and prolonged heating period of up to 4 hours is possible with the use of PCM-based warmer. Repeated use of the mattress is possible by re-warming the mattress to exhibit a phase change from solid to liquid, either by immersion in boiling water or by electric heating. A disadvantage of this PCM mattress is of its single fault design, i.e., as the phase changes, the material becomes solid, and thus, quite uncomfortable for the infant. 
         [0014]    The present disclosure is intended to eliminate hypothermia by providing a means of enthalpy exchange between the energy sources (primary, secondary heat sources, and the patient). The secondary heat source is capable of maintaining normothermia by using baseline power, which is highly efficient. This baseline power can be generated via a self-regulating, printed circuit board-based resident matrix heater, embedded within a warm primary heat source (e.g., within a gel or PCM mattress) and powered by a battery such as a widely available car battery. In doing so, a further intention is to virtually eliminate the need to remove the infant from the “kangaroo pouch” during the first days of his or her life thereby minimizing additional risks associated with disturbing fragile infants and improving patient safety. 
         [0015]    The present disclosure is novel in that heat provision to the infant may be sustained in-situ for an extended period, through the efficient use of a secondary mechanism for warming a primary medium and maintaining normothermia with respect to the ambient surroundings. Also novel is monitoring of the temperatures of the patient and others (primary, secondary sources, and ambient environment) including available battery power, leading to smarter algorithms and simple, easy-to-use instructions with audio/visual alarms. Ambient noise disturbances from surroundings and from the alarms generated by the electronics can be reduced with the help of noise attenuating foam pads over the infant&#39;s ears. 
         [0016]    The primary material can be composed of organic, inorganic, hygroscopic, clay based materials or combination thereof. The gel or phase change material-based primary medium should have an optimum circuit dependent on the heat capacity of the primary source, the available input power and the time required to maintain secondary heating based on the ambient environment. By maintaining minimum or baseline heating of the primary heat source, the need for maximum heater power for the secondary heat source over extended periods may not be necessary, thereby making the system highly efficient. In addition, providing minimal heating may also eliminate wide enthalpy fluctuations seen with the gel/PCM mattress alone as they transition through the warm and cold stages. 
         [0017]    Under the present disclosure, minimum enthalpy exchange is anticipated between the patient, primary medium and secondary network, considering the ambient environment with little or no thermal cycling, which, in turn, results in uniform infant warming. One or more novel embodiments operating between 10-50 W, with the use of up to two 12V batteries intended to provide uninterrupted heat for 20-24 hours is discussed. It should also be evident to one skilled in the art of accomplishing enthalpy exchange using heating mechanisms outside the gel/PCM mattress or combination thereof. Secondary heating mechanisms other than use of resistive networks, for example, such as with thermoelectric networks, is possible. With such mechanisms, cooling is also possible. Clearly, the benefits of maintaining normothermia in the first few days of infant life and reducing infant handling is necessary in remote areas of developing countries until standardized healthcare is accessed. The need for a simpler, more practical infant warming therapy in the first few days of life is now apparent. 
         [0018]    The device in accordance with the invention provides safe warming therapy to infants in the first few days of life, through an interactive enthalpy exchange between primary and secondary heat sources, in combination with the patient. System power consumption is optimized in accordance with the ambient environment for a period of 1-2 days, through the use of a fully charged battery, such as a widely-available car battery. 
         [0019]    To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a graphical representation of the power for heating a phase change material (PCM), including its temperature behavior illustrating heat retention capacity suitable for warming the infant at different ambient temperatures 
           [0021]      FIG. 2  is a graphical representation of power for maintaining operator set temperature for an infant incubator or infant warmer at different ambient temperatures. 
           [0022]      FIG. 3  is a simplified graph of power versus time required by expensive commercial incubator/warmer (a), to heat a given phase change material (b) and proposed invention using feedback mechanisms to optimize power at a given ambient temperature (a, c). 
           [0023]      FIG. 4A  represents a simple secondary network for adjusting power supply to an interactive enthalpy exchange system.  FIG. 4B  shows a pulse cycle of the power supply via the secondary network of  FIG. 4A . 
           [0024]      FIG. 5A  shows another secondary network for adjusting power supply to the interactive enthalpy exchange system in accordance with the present disclosure.  FIG. 5B  represents a pulse cycle of the power supply via the secondary network of  FIG. 5A . 
           [0025]      FIG. 6  shows a preferred embodiment of the interactive enthalpy exchange system with an infant patient placed within a pouch in accordance with the present disclosure. 
           [0026]      FIG. 7  is an infant holding sectional schematic of a control/display unit, an efficient warming cocoon showing all layers—covers, foam cushion, primary, secondary heat sources and connection to a battery of the interactive enthalpy exchange system of  FIG. 6  in accordance with the present disclosure. 
           [0027]      FIG. 8  shows an embodiment of a secondary resistive heating circuit that spans the surface area encompassed by the medium of the primary heat source in accordance with the present disclosure. 
           [0028]      FIG. 9  is another embodiment of a secondary resistive heating circuit in accordance with the present disclosure. 
           [0029]      FIG. 10  is a flow chart illustrating exemplary steps that may be executed to maintain enthalpy by an interactive enthalpy exchange system between primary and secondary sources including the patient, all being ambient sensitive. 
       
    
    
     DEFINITIONS 
       [0030]    The term infant (from the Latin word for infans, meaning unable to speak or speechless) relates to a newborn infant, premature or otherwise, and small babies generally from birth up to one year of age. 
         [0031]    The term transport relates to safely moving the infant patient with all of his or her life sustaining equipment and monitoring tools from remote areas to a standardized healthcare setting 
         [0032]    The term enthalpy is a thermodynamic state function. It is used here to simplify energy transfer between systems; the patient, primary and secondary heating sources, and the environment. The total enthalpy, H, of a system cannot be measured directly, only the change in enthalpy, ΔH. The ΔH is a positive change in endothermic reactions, and negative in heat-releasing exothermic processes. 
         [0033]    The phrase enthalpy of fusion also known as (latent) heat of fusion (or thermal heat capacity) refers to the change in enthalpy resulting from heating a given quantity of a substance to change its state from a solid to a liquid. The temperature at which this occurs is the melting point. Thermal heat capacity depends on the amount of material and is specified in joules/gram (SI unit). 
         [0034]    The phrase modular system relates to an interactive enthalpy exchange system assembled with individual components such as a kangaroo pouch, a battery holding transporter, a user interactive control/display unit, the system capable of being quickly assembled or disassembled for ease of installation, de-installation, service, trouble shooting, satisfy design constraints, usability etc. 
       DETAILED DESCRIPTION 
       [0035]    The present disclosure enhances infant comfort with a mattress (e.g., gel-based mattress). By providing the means for secondary warming via a self-regulating, battery powered, resident matrix heater embedded within the warm gel mattress, the need to move the infant from a “kangaroo pouch” during the first days of the infant&#39;s life is virtually eliminated. 
         [0036]    The aim of the present disclosure is to sustain heat provision to the infant in situ for an extended period, with an additive, secondary heat source embedded within the already warm gel mattress, the secondary heat source capable of heat provision on its own. By maintaining minimum or baseline heating of the gel based substrate, the need for maximum heater power over extended periods can be eliminated, thereby making the system more efficient. In addition, providing minimal heating may also eliminate the temperature fluctuations of the substrate, and therefore, stabilize heat provided to the infant. The preferred embodiments of the present disclosure describe the use of 10 W-50 W resistive matrix heating power, embedded in a gel-based inorganic or organic substrate mattress and powered by one or more 12V batteries, as to provide uninterrupted heat for 1-2 days in controlled environment settings of 20° C., 25° C. and 30° C., respectively. Sensor dependent and independent feedback is used in several places to improve performance, safety and effectiveness of the device. Software-independent hardware measures are incorporated to minimize risk while enhancing patient, operator and equipment safety. Operator visual and audio alarms are incorporated to regulate power based on the temperatures of the patient, primary and secondary heating sources and the environment and the available battery power. Recharging of the batteries is possible with widely-available, routine means available everywhere. 
         [0037]    Referring initially to  FIG. 1 , shown is a graphical representation of the typical amount of supply power for heating a gel/phase change material, including the temperature characteristics  10 ,  12 ,  14  of the chosen gel/phase change material, illustrating its heat retention capacity suitable for warming the infant at different ambient temperatures. The solid-dark line  16  shows when the power is ON to heat the gel/phase change material. Once the gel/phase change material crosses the set temperature, the heat is turned OFF. With this transient change in power, it takes a few minutes for the gel/phase change material to stabilize its enthalpy. Then, steady state is maintained for a few hours depending on the properties of the gel/phase change material including its heat retention capacity and exchange with the subject. Primary heat sources with heat storage capacity of 100 J/g (joules/gram), typically around 200 J/g are preferred, whereas phase transition temperatures of anywhere from 30-46° C. are desired. 
         [0038]    After a few hours, as enthalpy difference with the subject increases, temperature of the gel/phase change material of the primary heat source drops as it loses heat. Temperature drop of the gel/phase change material below the patient skin temperature of 37° C. can be detrimental to the infant. That is, instead of keeping the infant warm, the body heat from the infant may be drawn away, which can lead to hypothermia if left untreated. This is exacerbated at the low ambient temperatures, for e.g., 20° C. Here, it takes longer to maintain the liquid phase of the phase change material; the shorter the meaningful enthalpy exchange, the more drastic is the cooling off of the primary heat source, rendering the thermal conditions highly undesirable for the infant. At higher ambient temperatures, e.g., 30° C., the effect is quite the opposite; i.e., the quicker it is to go past transition temperatures, the longer the heat retention and the slower the temperature drop off. Thus, a controlled mechanism is needed to maintain normothermia for the infant, based on the ambient environment temperature. 
         [0039]    Moving to  FIG. 2 , shown is a graphical representation of the power expended to maintain operator-set temperature and heat-rise curves  10 ′,  12 ′,  14 ′ for an expensive infant incubator or an inefficient, commercially available infant warmer at different ambient temperatures (20° C., 25° C. and 30° C.). Temperature heat-rise curves illustrate damped oscillations to reach equilibrium, whereas typical power curves  16 ′ to reach operator-set temperature are shown to illustrate different phases; during warmup and steady-state, respectively, at 25° C. As temperature rises to operator set values, power lowers from 100% to whatever is necessary to maintain steady-state at the operator-set temperature. Algorithms and electronics are employed based on feedback control theory. Once the power is lost, cooling begins immediately. These incubators and warmer devices need high power for operation (of the order of 300-500 W) and require rigorous cleaning/disinfection procedures to eliminate cross-contamination between the patients who reside in them for up to 1 month. These devices are not suitable for use in remote areas and are not suitable for transport. 
         [0040]      FIG. 3  shows simplified power graphs of the power supply to an interactive enthalpy exchange system in accordance with the present disclosure, representing amount of power for heating a gel/phase change material of the primary heat source past its transition temperature (a), to show power expended in a conventional incubator/warmer (b), and to highlight current application of the battery operated, primary-secondary supportive, enthalpy-maintaining mechanism (c). With reference to the gel/phase change material based warming (a), either the power is ON to warm the material or OFF resulting in a single heating phase. With respect to the bi-phasic heating cycle of a conventional incubator/warmer (b), heating begins with full power at start which reduces gradually as temperature rises and approaches steady-state. Algorithms based on feedback control from sensors regulate power to maintain steady-state over an extended period. 
         [0041]    Transition rate from state I to state II depends on the size of the incubator/warmer, heater size, temperature setting and air flow pattern. Very small variations computed by algorithms based on feedback sensors are expected in state II to maintain steady-state. With continued reference to  FIG. 3 ( c ) , multi-phase heating with maximum power in the beginning, followed by deregulation of power, then cycling is anticipated to maintain steady-state for an extended period. Maximum power in the beginning (Phase I) helps transition the gel/phase change material of the primary heat source, i.e., inherit enthalpy, whereas transition from I to II will help maintain enthalpy over an extended period (Phase II) followed by cycling (Phase III), if necessary, to retain enthalpy of the system necessary and provide consistent warmth to the infant. 
         [0042]    The concept is clear: maximum power (state I) allows heating of the primary heat source, so enthalpy of the system can be maintained for a few hours. The primary heat source can be heated two ways by utilizing maximum power from ambient cold state to arrive at the set temperature: 
         [0043]    a) independently by dipping in a hot water bath, or by placing between parallel heater plates etc. or by any other means (air convection, optical, etc.) or their combination OR 
         [0044]    b) the secondary heat source. 
         [0000]    Alternately, a combination can be utilized. 
         [0045]    State I indicates maximum power provided to the primary heat source (gel/phase change material) via an independent means or by the secondary heat source or their combination to arrive at or near the set temperature from ambient cold (resting) state. Since greater amounts of enthalpy has to be transferred to the system at the ambient, resting ground state, the power needed in Phase I can be maximum of the three states (I-III). 
         [0046]    The reduced power state II assists to maintain enthalpy as the heat capacity of the primary heat source begins to vane. State III regulates power efficiently, one way by cycling as the gel/phase change material approaches the transition temperatures, to ensure the overall system enthalpy is maintained. In addition, states II and III extend power to withstand changes in the ambient environment and adapt to infant body temperatures. Amplitudes of state II and III and the cycling of state III (time ON versus OFF) can be manually set by carefully designing the secondary resistive networks so that their impedance is altered to support warming over an extended period (e.g., 1-2 days). In addition, instructive audio and visual alarms allow the user/operator to dial switches per concepts shared in  FIGS. 4A-B , and  8 ,  9 , to permit alteration of states II and III. 
         [0047]      FIG. 4A  is a simple representation of adjusting power supply level, by a secondary network  20  which varies voltage/current to a load resistor R 1  for a voltage input V and current I, with a manual or electronic switch S 1 .  FIG. 4B  represents a pulse cycle  26  of the power supply to the secondary network  20  of  FIG. 4A . A closed switch S 1  allows current to pass through the resistor R 1 , and thus, generates power (P=I 2 R 1 ). With the switch S 1  open in the secondary network  20 , there is no current across the resistor R 1 , and thus, resulting in zero power. The power expended by the secondary network  20  may help to generate or maintain the gel/phase change material of the primary heat source above the transition temperature which, in turn, provides warmth to the infant. 
         [0048]      FIG. 5A  is another simple embodiment of the pulse cycling approach of  FIGS. 4A-B  with the secondary network  20 ′ having two load resistors (R 1 , R 2 ) for a voltage input V and total current I. An open switch S 2  allows current to pass through a second resistor R 2 , forcing the secondary network  20 ′ to provide low power to the interactive enthalpy exchange system. With the switch S 2  closed, current divides through the resistors R 1  and R 2 . Specifically, where the resistors R 1  and R 2  are connected in parallel and resistance value of the first resistor R 1  is greater than or equal to the resistance value of the second resistor R 2  but less than or equal to five times of the resistance value of the second resistor R 2 , it results in overall reduced resistance, which, in turn, allows more current to flow, and therefore, generates higher power than having the second resistor R 2  alone as in  FIG. 4A . Likewise, when the resistance value of first resistor R 1  is equal to the resistance value of the second resistor R 2 , the secondary network  20 ′ will result in twice the power. When the resistance value of first resistor R 1  is less than or equal to the resistance value of the second resistor R 2 , the secondary network  20 ′ can generate other powers accordingly. Deviation of the combined R 1 -R 2  resistance from the second resistor R 2  alone as in  FIG. 4A  will determine the difference between low and high power supplies (low power=I 2 R 2 , high power=I 1   2 R 1 +I 2   2 R 2 ; I=I 1 +I 2 ) generated as a result. A simple parallel combination with one switch, S 2 , in series with the first resistor R 1  is shown in  FIG. 5A . However, other combinations are possible (e.g., a series-parallel combination).  FIG. 5B  shows for power amplitude alteration  26 ′ along with cycling using the secondary network  20 ′ of  FIG. 5A . Power curve shows by altering the position of the S 2  switch, different power levels (low, high) can be achieved since the resistance of the system will be altered. With S 2  closed, R 1  is in parallel with R 2 . With S 2  open, R 1  is out of the circuit and the total resistance of the system is altered. In the former case, current is shared by R 1  and R 2 , whereas in the latter case, current flows solely through R 2 . Without cycling, there can be only two power stages (low, high) with 100% duty cycle which can lead to over-heating and inefficient use of the available battery power. Power cycling at any level can be accomplished by altering the load with the use of simple timer circuits (e.g., timer circuit for aquariums that work on AC), at lower DC voltages anywhere between 6-24 VDC. A careful manipulation of both amplitude alteration and cycling will permit an efficient use of the available battery power needed to provide energy to the primary/secondary system, and thus, maintain enthalpy in the interactive enthalpy exchange system  40 . This will, in turn, prolong or sustain infant warmth over an extended period. 
         [0049]      FIG. 6  describes a preferred embodiment of a system in accordance with the invention. The modular system  40  includes three sections: a “kangaroo” pouch  42 , a control/display unit  44  and a battery holding transporter  46 . The “kangaroo” pouch  42  and restraining mechanism (e.g. straps  48 ) may be designed for stationary use or transport care. “X” shaped straps  48  that go around the entire package can be used to carry the infant or attach to a transport means. Not shown are the combined primary/secondary heat module and pocket for holding the same which are discussed later with respect to the pouch sectional view in  FIG. 7 . Further details of the pouch  42  are not discussed here, but it is left to the reader to surmise a form fit solution to ensure maximum contact with the warming medium of the primary heat source and less exposure of the torso to ambient, with full access to the face/mouth for feeding and complete visual. A cap may be used to cover the head of the infant and the pouch  42  may cover the head to prevent heat loss. Ear plugs (not shown) of sorts may be used to reduce ambient noise disturbance to the infant. 
         [0050]    The control/display unit  44  may be water-tight, rugged, portable, and user interactive. The control/display unit  44  includes a switch to turn on or off the interactive enthalpy exchange system  40  and LED lights  50  for indicating system status to the user. The control/display unit  44  may also include sensors  52  to sense temperatures. The control/display unit  44  may also include a display  52  for displaying temperatures of the patient, primary and/or secondary heating sources (discussed further later), and the ambient temperature. The control/display unit  44  may be normally attached to the pouch  42  and can be easily removed and attached to the battery holding transporter  46 . Power and sensor cables  54 ,  56  can be merged into one for increased usability and maintain a simple design. The cable(s)  54 ,  56  can be removed or attached with a connector to the pouch  42  and the control/display unit  44 . Likewise, a detachable power cable  42  can be used between the battery holding transporter  46  and the control/display unit. The control/display unit  44  has means of communication with the user by way of audio/visual alarms (e.g., audio speaker  60 ), control knobs  62  and bright LED lights  50 . A service connection behind (not shown) allows debugging and software upgrade functions to be performed efficiently without the need to open the control/display unit  44 . 
         [0051]    Only a side view of the battery-holding assembly  46  is shown. The battery-holding transporter  46  may have wheels  64  (e.g., plastic or rubber wheels) as a transporting mechanism. The battery holding transporter  46  may be designed like an oxygen tank holder and may house batteries (e.g., car batteries  66 ) inside a battery enclosure  68 . The battery enclosure  68  may be fire-proof, water-tight, and of plastic material with very high dielectric, so as to ensure safety during rain, lightning, in high static areas and at low temperatures with very low humidity levels (e.g., &lt;20% rH). Flame rated batteries may be used. Batteries  66  may be held so there is no motion inside the battery enclosure  68 . A battery charging plug/cable (not shown) may be provided, so that the batteries  66  can be charged by an external charger without having to remove the batteries  66 . Inline charging and thermal fuses can be employed in the design for safety. The battery enclosure  68  may be placed on top a vibration dampener  70  to smooth the vibrations otherwise felt by the batteries  66  during motion. Likewise, during stationary use a rubber stopper  72  can serve as a vibration dampener  70  and for improved stability. 
         [0052]      FIG. 7  shows a sectional view of an infant patient wrapped in the pouch  42  connected to the control/display unit  44 , showing layers of the pouch  42 —inner cover  74 , outer cover  76 , temperature insulator  78 , foam cushion  80 , primary heating source (e.g., PCM/Gel Material  82 ), secondary heating source (e.g., secondary resistive heating  84 ) and connection  86  to battery  66 . The pouch  42  may be of a “kangaroo style” wrap made from polyethylene or nylon or polystyrene plastic material capable of withstanding a wide temperature range (e.g., −20° C. to 90° C.). The pouch is easy to disinfect through the use of local agents and can be held with Velcro straps to completely encompass the infant without covering the face, as to allow for direct visualization and feeding (not shown). The outer polyethylene layer, with a low temperature coefficient (k&lt;0.25 BTU-in/hr-ft 2 -° F.), also functions as a temperature insulator which is intended to maintain the heat within the infant wrap pouch  42  and insulate it from the external environment. This is also to ensure that the temperature of the inner cover  74  does not exceed 40-42° C., prohibiting overheating from outside the wrap sources of heat (i.e. direct exposure to sun light, proximity to a heater or stove etc.). The foam cushion  80  forms an inner, protective cushion support for the infant. The gel/phase change material of the primary heat source  82  and secondary resistive heat source  84  are encompassed in the pouch  42 , which may be removable for possible replacement below the infant. It is preferred that the gel medium of the primary heat source  82  has a heat retention capacity (or latent heat of fusion, or thermal storage capacity etc.) of roughly 200 J/g. Higher values are preferred but normally come with additional restraints such as higher powers needed for phase transition etc. Likewise, a choice of organic, inorganic, eutectic salts, hygroscopic materials are also important to ensure optimum performance of the interactive enthalpy exchange system  40 . For example, chemically stable properties such as the high heat of fusion, the ability to melt congruently, and safe and non-reactive behavior are the preferred characteristics of organic material. However, the low thermal conductivity and low volumetric latent heat storage capacity in their solid states require high heat transfer rates. This is avoided in the current application during use of the novel secondary heat source, concepts and circuits discussed in  FIGS. 4, 5, 8, and 9 , respectively. In addition, care should be taken to insulate the electronics, so as to avoid the embedded secondary resistive heater matrix come in direct contact with the gel/phase change material of the primary heat source  82  and cause a short-circuit. Short circuits alter circuit impedance, current patterns, the overall battery power expended and can result in hot spots. Insulation can be accomplished with the use of high temperature epoxy glues that are flexible. In addition, inline current limiting and thermal fuses can be employed to mitigate adverse events. 
         [0053]    Connections to the battery  66 , sensor locations and the audio/visual alarm display panel  52  for user interface are all partially shown. Sensors SN 1 -SN 4   58 , obtain temperatures of the infant, primary heat source  82 , secondary heat source  84  and ambient environment for feedback. Low and high temperatures past a pre-set chosen window for safe operation including low-battery state trigger audio/visual alarms, which prompt the user to take future course of action. Sensing and feedback circuitry can be analog, digital or their combination. The secondary heat source  84  can be resistor based or via other means (e.g., thermoelectric circuits). Compact piezoelectric speakers with high audible alarms in the range of 80-100 dBA are preferred, audio alarms can be paused for a brief time period depending on fault priority (low, medium or high). Visual alarms may be LED or LCD based or their combination. Audio alarms may be via beeping based on (low, medium, high) priority and or in local language for user interaction. 
         [0054]      FIG. 8  shows one embodiment of the exemplary secondary heat source  84 ′ employed in this application that overlaps completely, and partially spans the surface area occupied by the gel/phase change material of the primary heat source  82 . This thirty-one count resistor (R 1 ) network  84 ′ is driven symmetrically in two places per lead connection which are connected to the battery +/− terminals via the electronics and display (not shown). The idea of the two-fold symmetrical connection is to normalize the current in every rung. This results in a uniform current distribution, and therefore, uniform heating based on the resistive heating explained above (I 2 R) of the gel/phase change material of the primary heat source by absorbing sufficient thermal energy from the secondary heat source  84 ′ to maintain its own enthalpy (endothermic reaction, +ΔH), while releasing (exothermic reaction, −ΔH) uniform heat to the infant. 
         [0055]      FIG. 9  is another embodiment of the secondary heat source  84 ″. This secondary sixteen resistor network  84 ″ has a simple parallel-series connection which results in total resistance of  4 R 2  (resistance of one rung consisting of four R 2  resistors in series) when the resistance values of R 2  and R 3  are equal. This allows for equal current distribution in all rungs, resulting in uniform heating of the secondary heat source  84 ″ if each resistor (R 2 , R 3 ) were physically placed equidistant from one another (in two-dimensions as shown). With R 1 =5Ω, R 2 =R 3  and two 12 VDC batteries (I=1.2 A, P=28.8 W), the secondary sixteen resistor network  84 ″ can reach 80-100° C. in 5 minutes in room air. When embedded in a gel/phase change material of the primary heat source, the maximum temperature can reach 40-50° C., sufficient to maintain the gel/phase change material of the primary heat source above its transition temperature. Heating of the gel/phase change material of the primary heat source  82  from its coldest state is gradual and can take up to 30 minutes, whereas maintaining enthalpy of the interactive enthalpy exchange system  40 , once steady-state is reached, is much faster and very efficient, through the alteration of the power levels and cycling, concepts explained in  FIGS. 4 and 5 , respectively. By concomitantly reducing the battery voltage from 24V to 12V DC and total rung resistance to 10Ω, a less-bulky, 14.4 W system demanding careful choice of gel/phase change material of the primary heat source/secondary heat source and component values will be created. Batteries generally having 55-60 AH capacities should provide enough power for secondary heating for 1-2 days. Note that car batteries can be recharged to full capacity using a locally available low-cost charger. 
         [0056]    In unique cases when non-uniform heating is required per physical design, demands of the infant mattress or that of the enclosure, is possible when R 2 ≠R 3 . Unequal resistors result in different currents in the rungs, and therefore, intentionally, selective non-uniform heating pattern, targeting the region of interest. This sort of a selective, targeted heating pattern can be advantageous, for example, in instances where full heating of the gel/phase change material of the primary heat source  82  directly under the infant head is not desired. Total resistance of the secondary resistive network  84 ″ of  FIG. 9  can be 2(4R 2 ∥4R 3 ). Based on these two secondary heating patterns, other variations can be practiced by those skilled in the art. The outer plastic covers  76  can be molded along with the gel/phase change material of the primary heat source  82  alongside the resistor networks with a connector for seamless insertion in to the “kangaroo pouch”  42 . 
         [0057]      FIG. 10  illustrates exemplary steps that may be executed to maintain enthalpy by an interactive enthalpy exchange system  40  among primary heat source  82  (e.g., a gel/phase change material medium), secondary heat source  84  and the patient, all being ambient sensitive. The exemplary method  100  may be carried out by executing the steps via a processor and memory, where the logical operations are stored in the memory. Thus, the flow chart of  FIG. 10  may be thought of as depicting steps of a method carried out by an electronic device, such as a controller or the like. Although  FIG. 10  shows a specific order of executing functional logic blocks, the order of executing the blocks may be changed relative to the order shown. Also, two or more blocks shown in succession may be executed concurrently or with partial concurrence. Certain blocks also may be omitted. In addition, any number of functions, logical operations, commands, state variables, semaphores or messages may be added to the logical flow for purposes of enhanced utility, accounting, performance, measurement, troubleshooting, and the like. It is understood that all such variations are within the scope of the present invention. 
         [0058]    Two modes of operation possible are heating and ambient modes. In the heating mode, sensor dependent and independent feedback are used in several places throughout the interactive enthalpy exchange system  40  to improve performance, safety and effectiveness of the system. In the ambient mode, power is deliberately cut but continued sensing is possible. The ambient mode is desired when no-heating is required or when over-heating continues to occur and user interaction is repeatedly necessary. 
         [0059]    Beginning at step  102 , it is determined whether a resistive load is present on the interactive enthalpy exchange system  40 . If at step  102 , it is determined that no resistive load is present in the interactive enthalpy exchange system  40 , then the method moves to step  104 . At step  104 , power is removed and an alarm is displayed at the display unit ( FIG. 7  ( 52 )) of the control/display unit  44 . However, at step  102  if a resistive load is determined to be present, then the method  100  moves to step  106 . At step  106 , it is determined whether an infant patient is also present in the modular system  40 . If at step  106 , the infant patient is determined to be present in the modular system  40 , then the method moves to step  108 . At step  108 , it is determined whether the skin temperature of the infant patient is greater than or equal to 36° C. If it is determined that the skin temperature of the infant patient is not greater than or equal to 36° C., then the method moves to step  110 . At step  110 , the power supply to the modular system  40  is raised to the full level, and the method moves to step  112 . If, at step  106 , it is determined that the infant patient is not present in the modular system  40 , then the method moves to step  112 . 
         [0060]    At step  112 , it is determined whether the temperature of the gel/phase change material of the primary heat source  82  is greater than or equal to 32° C. If it is determined that the temperature of the gel/phase change material of the primary heat source  82  is greater than or equal to 32° C., then the method moves to step  114 . At step  114 , the power supply level to the modular system  40  is calculated and the method moves to step  118 . If, however, at step  112  it is determined that the temperature of the gel/phase change material of the primary heat source  82  is not greater than or equal to 32° C., then the method moves to step  116 . At step  116 , it is determined whether the temperature of the secondary heat source  84  is greater than or equal to 1.25 times the temperature value of the gel/phase change material of the primary heat source  82 . If it is determined that the temperature of the secondary heat source  84  is greater than or equal to 1.25 times the temperature value of the gel/phase change material of the primary heat source  82 , then the method moves to step  118 . If, however, it is determined that the temperature of the secondary heat source  84  is not greater than or equal to 1.25 times the temperature value of the gel/phase change material of the primary heat source  82 , then the method moves to step  110  at which the power supply to the modular system  40  is raised to the full level, then the method moves to step  112 . 
         [0061]    Now, at step  118  the ambient temperature is measured and the method  100  proceeds to step  120 . At step  120 , the ambient state (AMB 1  through AMB 4 ) is determined from the measured ambient temperature. AMB 1  indicates the measured ambient temperature is less than 15° C. AMB 2  indicates the measured ambient temperature ranges from 15° C. to 20° C. AMB 3  indicates the measured ambient temperature is greater than 20° C. and ranges up to 25° C. AMB 4  indicates the measured ambient temperature is greater than 25° C. and ranges up to 30° C. As will be appreciated, the specified ambient states are exemplary, and different and/or additional temperature ranges can be used as required by the specific application. At step  120 , a single condition for ambient temperature is confirmed from the four possibilities based on the measured temperature and low powers applied (LPs of e.g., 66%, 50%, 37% or 25% duty cycles) to the system from the algorithm by way of pre-determined pulse width adjustments. Greater duty cycle reflects greater amounts of energy calculated to maintain the system enthalpy, since energy is a product of power and time, whereas power is a product of voltage and current. 
         [0062]    Upon determination of the ambient state at step  120 , the method moves to step  122  where it is determined whether the measured ambient temperature is greater than 30° C. If the ambient temperature is not greater than 30° C., then the method moves to step  124 A where the appropriate powers are re-calculated to reflect one of the AMB 1  through AMB 4  states by adjusting the duty-cycle of the heater pulses based on the ambient temperature measurement of step  118 . At  124 A, constant power is used, whereas the calculated energy for the four ambient states (AMB 1  through AMB 4 ) are proportional to the heater pulse-width, i.e., duty-cycle (ON versus OFF time). At higher ambient temperatures, it takes less energy to maintain steady state, since maintaining system enthalpy by providing warmth via one or more heat sources is desired. The exact percentages to calculate energy in the four ambient states (AMB 1  through AMB 4 ) can be determined experimentally. If the ambient temperature is determined to be less than 15° C. (AMB 1 ), at step  124 A low energy with duty-cycle of 66% is provided to the interactive enthalpy exchange system in order to maintain the enthalpy. If the ambient temperature is determined to be in a temperature range from 15° C. to 20° C. (AMB 2 ), at step  124 A low energy with duty-cycle of 50% is provided to the interactive enthalpy exchange system in order to maintain the enthalpy. If the ambient temperature is determined to be greater than 20° C. and up to 25° C. (AMB 3 ), then the method continues to step  124 A at which low energy with duty-cycle of 37% is provided to the interactive enthalpy exchange system in order to maintain the enthalpy. If the ambient temperature is determined to be greater than 25° C. and up to 30° C. (AMB 4 ), then the method continues to step  124 A at which low energy with duty-cycle of 25% is provided to the interactive enthalpy exchange system in order to maintain the enthalpy. If, however, at step  122  the ambient temperature is determined to be greater than 30° C., then the method continues to step  124 B. At step  124 B it is determined if the skin temperature of the infant is greater than or equal to 37.5° C. If the skin temperature of the infant is greater than or equal to 37.5° C., then the method moves to step  104  in which power is removed and an alarm is displayed at the display unit  52  of the control/display unit  44 . If, however, the skin temperature of the infant is not greater than or equal to 37.5° C., then the method moves to step  102  and repeats. 
         [0063]    In short, temperature deviations trigger software functions pre-programmed to check for infant, primary, secondary and ambient values, continually to ensure the system is functioning properly and within safe limits. Temperature feedback and resulting regulation to maintain infant body temperatures close to 37° C. is based on the skin temperature, continually monitored, for example, at the axilla (under the arm) or preferably the torso using a modified feedback-control theory based proportional-integration-derivative (PID) algorithm suited to this warming system. It is worth noting, modified PID algorithms may be used for different patient, the medium used in the primary heat source, secondary heat source and ambient temperature segment ranges; for example, ambient &lt;15° C., 15-20° C., &gt;20-25° C., &gt;25-30° C. and &gt;30° C., respectively. Regardless, when the infant skin temperature exceeds 37.5° C. or when the ambient surroundings exceed 30° C., power to the heater will immediately be cut to prevent overheating. 
         [0064]    In addition, heater power and energy calculated by this modified PID algorithm can be up or down regulated, based on the low or high ambient environments (AMB 1 -AMB 4  on  FIG. 10 ), so as to maintain the primary temperature, and thus, the infant at steady-state. This additional regulation is important because elevated environments support overheating; whereas lower ambient environments support heat depletion, resulting in under-heating; either outcome negatively affects the patient. This can be dangerous when moving the infant from a colder environment, such as outside the house to the inside. 
         [0065]    This ambient environment measurement feature was also useful in regulating power, i.e., maintaining adequate heater power without overheating. Pouches are often left open for extended periods of time when caregivers attend to the patient, or when a mother is feeding the infant. Software-independent hardware measures are incorporated to minimize risk while enhancing patient, operator and equipment safety. It is worth noting that several versions of the algorithm can be written by any skilled persons in the art. The operational flow-chart of  FIG. 10  is a sample algorithm representation of the degrees of freedom available in determining constraints for temperature readings, obtained by the sensors (SN 1  through SN 4 ). Additional sensors can be added for redundancy to validate temperature measurements. Likewise, accurate power calculation and available battery charge are possible with voltage divider based resident circuits. 
         [0066]    Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.