NOVEL DESIGNS FOR AN ELECTRIC WARMING BLANKET INCLUDING A FLEXIBLE HEATER
An electric warming blanket includes a flexible heater that may be enclosed within a flexible shell, which is, preferably, water resistant and may extend beyond lateral edges of the heater to support stiffening members. A layer of non-conductive flexible porous material may be bonded to one or both sides of the heater. When the heater is enclosed in the shell, a layer of thermal insulation may be disposed between one side of the heater and the shell. A temperature sensor may be coupled to the heater at a location where the heater will be in conductive contact with a body when the blanket is draped thereover, and at least one super-over temperature sensor may also be coupled to the heater; the at least one super over-temperature sensor is adapted to interrupt a supply of power to the heater.
The present application claims priority to co-pending provisional applications Ser. No. 60/825,573, entitled HEATING BLANKET SYSTEM filed on Sep. 13, 2006; Ser. No. 60/722,106, entitled ELECTRIC WARMING BLANKET INCLUDING TEMPERATURE ZONES AUTOMATICALLY OPTIMIZED, filed Sep. 29, 2005; and Ser. No. 60/722,246, entitled HEATING BLANKET, filed Sep. 29, 2005; all of which are incorporated by reference in their entireties herein.
RELATED APPLICATIONSThe present application is related to the following commonly assigned utility patent applications, all of which are filed concurrently herewith and all of which are hereby incorporated by reference in their entireties: A) ELECTRIC WARMING BLANKET HAVING OPTIMIZED TEMPERATURE ZONES, Practitioner docket number 49278.2.5.2; B) NOVEL DESIGNS FOR HEATING BLANKETS AND PADS, Practitioner docket number 49278.2.7.2; C) TEMPERATURE SENSOR ASSEMBLIES FOR ELECTRIC WARMING BLANKETS, Practitioner docket number 49278.2.9.2; D) BUS BAR ATTACHMENTS FOR FLEXIBLE HEATING ELEMENTS, Practitioner docket number 49278.2.16; and E) BUS BAR INTERFACES FOR FLEXIBLE HEATING ELEMENTS, Practitioner docket number 49278.2.17.
TECHNICAL FIELDThe present invention is related to electric heating or warming blankets or pads and more particularly to those including flexible heating elements.
BACKGROUNDIt is well established that surgical patients under anesthesia become poikilothermic. This means that the patients lose their ability to control their body temperature and will take on or lose heat depending on the temperature of the environment. Since modern operating rooms are all air conditioned to a relatively low temperature for surgeon comfort, the majority of patients undergoing general anesthesia will lose heat and become clinically hypothermic if not warmed.
Over the past 15 years, forced-air warming (FAW) has become the “standard of care” for preventing and treating the hypothermia caused by anesthesia and surgery. FAW consists of a large heater/blower attached by a hose to an inflatable air blanket. The warm air is distributed over the patient within the chambers of the blanket and then is exhausted onto the patient through holes in the bottom surface of the blanket.
Although FAW is clinically effective, it suffers from several problems including: a relatively high price; air blowing in the operating room, which can be noisy and can potentially contaminate the surgical field; and bulkiness, which, at times, may obscure the view of the surgeon. Moreover, the low specific heat of air and the rapid loss of heat from air require that the temperature of the air, as it leaves the hose, be dangerously high—in some products as high as 45° C. This poses significant dangers for the patient. Second and third degree burns have occurred both because of contact between the hose and the patient's skin, and by blowing hot air directly from the hose onto the skin without connecting a blanket to the hose. This condition is common enough to have its own name—“hosing.” The manufacturers of forced air warming equipment actively warn their users against hosing and the risks it poses to the patient.
Electric warming blankets overcome the aforementioned problems with FAW. Some of these warming blankets employ flexible heaters, which may be prone to potentially dangerous conditions, for example, when the blankets, including the flexible heaters, are folded over onto themselves. Such folding, which is sometimes called “rucking”, may result in electrical shorting between portions of the flexible heater. The short circuit becomes a relatively low-resistance pathway and current will preferentially flow through the low resistance area. The increased current flow may cause that area to get very hot which may cause a burn risk to the patient.
Electrical shorting with such heaters has been addressed by electrically insulating the heater by laminating a relatively thick layer of plastic film to each side of the heater. However, when electrical insulation is accomplished by laminating a relatively thick layer of plastic film to each side of the fabric heater, the resulting laminated structure becomes relatively stiff and non-flexible and does not exhibit desirable draping characteristics. A non-flexible, non-draping blanket is not only uncomfortable for the patient, but is also thermally inefficient because of the poor thermal contact with the patient. Non-flexible thermal blankets can also apply excessive heat and pressure to patient “high spots,” such as boney prominences.
Further, rucking may cause overheating of the flexible heater due to added thermal insulation over the side of the heater that is beneath a folded-over portion of the heater. Normally, the heater will lose heat off of both surfaces simultaneously. If the heater is folded back on itself, the upper layer of heater becomes a very effective guard heater. This near perfect thermal insulation on the upper side prevents the lower layer (e.g., the patient side) from losing heat to the environment. Therefore, the temperature of the lower of the two layers will increase to a new and higher equilibrium temperature. If the heater is folded like a “Z” so that there is an area that is three layers thick, the middle layer of the “Z” will not be able to lose heat from either of its surfaces. The area in the middle of the three-layer fold will significantly over-heat and may become unsafe.
A traditional approach to avoiding electrical shorting and/or overheating has been to purposefully make the blanket relatively stiff in order to prevent rucking. This stiffening is typically accomplished by laminating the heater material to plastic film or enclosing the heater in a relatively stiff outer cover. As previously discussed, stiff blankets may be uncomfortable for a patient and may be less efficient in heating the patient, since the stiffness prevents a draping of the blankets over the patient to maximize an area of the patient's skin receiving conductive as well as radiant heat transfer.
Accordingly, there is a need for a blanket that can avoid electrical shorting and/or overheating caused by rucking without becoming so stiff as to lose desirable draping characteristics. Various embodiments of the invention described herein solve one or more of the problems discussed above.
BRIEF DESCRIPTION OF THE DRAWINGSThe following drawings are illustrative of particular embodiments of the present invention and therefore do not limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements.
FIGS. 1B-C are end views of two embodiments of the subassembly shown in
The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides practical illustrations for implementing exemplary embodiments of the present invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements, and all other elements employ that which is known to those of skill in the field of the invention. Those skilled in the art will recognize that many of the examples provided have suitable alternatives that can be utilized. The term ‘blanket’, used to describe embodiments of the present invention, may be considered to encompass heating blankets and pads.
According to an exemplary embodiment, a conductive fabric comprising heating element 10 comprises a non-woven polyester having a basis weight of approximately 130 g/m2 and being 100% coated with polypyrrole (available from Eeonyx Inc., Pinole, Calif.); the coated fabric has an average resistance, for example, determined with a four point probe measurement, of approximately 15-20 ohms per square inch at about 48 volts, which is suitable to produce the preferred watt density of 0.2 to 0.4 watts/sq. in. for surface areas of heating element 10 having a width, between bus bars 15, in the neighborhood of about 20 inches. Such a width is suitable for a lower body heating blanket, some embodiments of which will be described below. A resistance of such a conductive fabric may be tailored for different widths between bus bars (wider requiring a lower resistance and narrower requiring a higher resistance) by increasing or decreasing a surface area of the fabric that can receive the conductive coating, for example by increasing or decreasing the basis weight of the fabric. Resistance over the surface area of the conductive fabrics is generally uniform in many embodiments of the present invention. However, the resistance over different portions of the surface area of conductive fabrics such as these may vary, for example, due to variation in a thickness of a conductive coating, variation within the conductive coating itself, variation in effective surface area of the substrate which is available to receive the conductive coating, or variation in the density of the substrate itself. Local surface resistance across a heating element, for example element 10, is directly related to heat generation according to the following relationship:
Q(Joules)=I2(Amps)×R(Ohms)
Variability in resistance thus translates into variability in heat generation, which is measured as a temperature. According to preferred embodiments of the present invention, which are employed to warm patients undergoing surgery, precise temperature control is desirable. Means for determining heating element temperatures, which average out temperature variability caused by resistance variability across a surface of the heating element, are described below in conjunction with FIGS. 2A-B.
A flexibility of blanket subassembly 100, provided primarily by flexible heating element 10, and optionally enhanced by the incorporation of flexible bus bars, allows blanket subassembly 100 to conform to the contours of a body, for example, all or a portion of a patient undergoing surgery, rather than simply bridging across high spots of the body; such conformance may optimize a conductive heat transfer from element 10 to a surface of the body. However, as illustrated in
The uniform watt-density output across the surface areas of preferred embodiments of heating element 10 translates into generally uniform heating of the surface areas, but not necessarily a uniform temperature. At locations of heating element 10 which are in conductive contact with a body acting as a heat sink, for example, body 16, the heat is efficiently drawn away from heating element 10 and into the body, for example by blood flow, while at those locations where element 10 does not come into conductive contact with the body, for example lateral portions 11, 12 as illustrated in
According to embodiments of the present invention, zones of heating element 10 may be differentiated according to whether or not portions of element 10 are in conductive contact with a body, for example, a patient undergoing surgery. In the case of conductive heating, gentle external pressure may be applied to a heating blanket including heating element 10, which pressure forces heating element 10 into better conductive contact with the patient to improve heat transfer. However, if excessive pressure is applied the blood flow to that skin may be reduced at the same time that the heat transfer is improved and this combination of heat and pressure to the skin can be dangerous. It is well known that patients with poor perfusion should not have prolonged contact with conductive heat in excess of approximately 42° C. 42° C. has been shown in several studies to be the highest skin temperature, which cannot cause thermal damage to normally perfused skin, even with prolonged exposure. (Stoll & Greene, Relationship between pain and tissue damage due to thermal radiation. J. Applied Physiology 14(3):373-382. 1959. and Moritz and Henriques, Studies of thermal injury: The relative importance of time and surface temperature in the causation of cutaneous burns. Am. J. Pathology 23:695-720, 1947) Thus, according to certain embodiments of the present invention, the portion of heating element 10 that is in conductive contact with the patient is controlled to approximately 43° C. in order to achieve a temperature of about 41-42° C. on a surface a heating blanket cover that surrounds element 10, for example, a cover or shell 20, 40 which will be described below in conjunction with
Referring now to the end view of
Returning now to
According to a preferred embodiment, assembly 421 includes a second, redundant, temperature sensor mounted to substrate 211, close enough to sensor 21 to detect approximately the same temperature; while sensor 21 may be coupled to a microprocessor temperature control, the second sensor, for example, a chip thermistor similar to sensor 21, may be coupled to an analog over-temperature cutout that cuts power to element 10, and/or sends a signal triggering an audible or visible alarm. The design of the second sensor may be the same as the first sensor and need not be described again. Another safety check may be provided by mounting an identification resistor to substrate 211 in order to detect an increase in resistance of element 10, due, for example, to degradation of the material of element 10, or a fractured bus bar; the optional identification resistor monitors a resistance of heating element 10 and compares the measured resistance to an original resistance of element 10.
According to some embodiments of the present invention, for example as illustrated in
According to some embodiments of the present invention, shell 20 includes top and bottom sheets extending over either side of assembly 250; the two sheets of shell 20 are coupled together along a seal zone 22 (shown with cross-hatching in the cut-away portion of
Returning now to
FIGS. 3C-D further illustrate a pair of securing strips 217, each extending laterally from and alongside respective lateral portions 11, 12 of heating element 10 and each coupled to side 13 of heating element 10 by the respective row of stitching 345. Another pair of securing strips 271 is shown in
With reference to
With further reference to
In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims. Although embodiments of the invention are described in the context of a hospital operating room, it is contemplated that some embodiments of the invention may be used in other environments. Those embodiments of the present invention, which are not intended for use in an operating environment and need not meet stringent FDA requirements for repeated used in an operating environment, need not including particular features described herein, for example, related to precise temperature control. Thus, some of the features of preferred embodiments described herein are not necessarily included in preferred embodiments of the invention which are intended for alternative uses.
Claims
1. An electric warming blanket, comprising:
- a flexible heater including a first side and a second side, at least one of the first and second sides having a surface area and a substantially uniform watt density output across the surface area when the element is electrically powered;
- a first layer of non-conductive flexible porous material bonded to the first side of the heater;
- a second layer of non-conductive flexible porous material bonded to the second side of the heater; and
- a first layer of water resistant material coupled to a second layer of water resistant material about a perimeter of the heater to form a substantially hermetically sealed space for the heater and the first and second non-conductive material layers bonded thereto.
2. The blanket of claim 1, wherein the heater comprises carbon.
3. The blanket of claim 1, wherein the heater comprises a nonconductive layer coated with a conductive material.
4. The blanket of claim 3, wherein the nonconductive layer of the heater comprises a woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
5. The blanket of claim 3, wherein the nonconductive layer of the heater comprises a non-woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
6. The blanket of claim 3, wherein the non-conductive layer of the heater comprises a non-woven cellulose material and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
7. The blanket of claim 1, wherein each layer of non-conductive flexible porous material comprises a woven fabric.
8. The blanket of claim 7, wherein the woven fabric is formed of a non-flammable material.
9. The blanket of claim 7, wherein the woven fabric is fiberglass or cotton.
10. The blanket of claim 1, wherein each layer of non-conductive flexible porous material comprises a non-woven fabric.
11. The blanket of claim 10, wherein the non-woven fabric comprises nylon or fiberglass.
12. The blanket of claim 1, wherein each layer of non-conductive flexible porous material comprises a polymeric foam.
13. The blanket of claim 1 wherein the first layer of water resistant material extends adjacent to the first layer of non-conductive flexible porous material and is un-adhered thereto.
14. The blanket of claim 13, wherein the second layer of water resistant material extends adjacent to the second layer of non-conductive flexible porous material and is un-adhered thereto.
15. The blanket of claim 1, further comprising:
- a first conductive bus bar coupled to the first side of the heater and extending alongside a first lateral edge of the heater; and
- a second conductive bus bar coupled to the first side of the heater and extending alongside a second lateral edge of the heater;
- wherein the first lateral edge is opposite the second lateral edge;
- the first and second bus bars are contained in the substantially hermetically sealed space formed by the first and second layers of water-resistant material; and
- the first and second bus bars are adapted for coupling to a power source for powering the heating element.
16. The blanket of claim 15, wherein the first and second bus bars comprise a metal wire.
17. The blanket of claim 16, wherein the metal wire is one of a plurality of braided metal wires.
18. The blanket of claim 15, wherein the first and second bus bars comprise a metal foil.
19. The blanket of claim 15, wherein the first and second bus bars comprise conductive ink.
20. The blanket of claim 15, wherein the first and second bus bars are coupled to the heater by sewn threads.
21. The blanket of claim 20, wherein the sewn threads are conductive.
22. An electric warming blanket, comprising:
- a flexible heater including a first side and a second side, at least one of the first and second sides having a surface area and a substantially uniform watt density output across the surface area when the element is electrically powered;
- a first layer of water resistant material disposed over the first side of the heater, being un-adhered thereto, and forming an outer surface of the blanket when the blanket is draped over an object or a person to be warmed;
- a second layer of water resistant material disposed over the second side of the heater, being un-adhered thereto, and forming an inner surface of the blanket, adjacent to the object or the person, when the blanket is draped thereover;
- the first layer of water resistant material coupled to the second layer of water resistant material about a perimeter of the heater to form a substantially hermetically sealed space for the heater; and
- a layer of thermal insulation disposed between the first side of the heater and the first layer of water resistant material.
23. The blanket of claim 22, wherein the heater comprises carbon.
24. The blanket of claim 22, wherein the heater comprises a nonconductive layer coated with a conductive material.
25. The blanket of claim 24, wherein the nonconductive layer of the heater comprises a woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
26. The blanket of claim 24, wherein the nonconductive layer of the heater comprises a non-woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
27. The blanket of claim 24, wherein the non-conductive layer of the heater comprises a non-woven cellulose material and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
28. The blanket of claim 22, wherein the layer of thermal insulation comprises a flexible polymeric foam.
29. The blanket of claim 22, wherein the layer of thermal insulation includes a plurality substantially parallel slits extending partially therethrough.
30. The blanket of claim 22, wherein the layer of thermal insulation includes a plurality of substantially parallel slits extending completely therethrough.
31. The blanket of claim 22, wherein the layer of thermal insulation comprises a high loft fibrous polymeric non-woven material.
32. The blanket of claim 22, wherein the layer of thermal insulation is attached to the heater.
33. The blanket of claim 22, wherein the layer of thermal insulation is un-attached to the heater.
34. The blanket of claim 22, further comprising:
- a first conductive bus bar coupled to the first side of the heater and extending alongside a first lateral edge of the heater; and
- a second conductive bus bar coupled to the first side of the heater and extending alongside a second lateral edge of the heater;
- wherein the first lateral edge is opposite the second lateral edge;
- the first and second bus bars are contained in the substantially hermetically sealed space formed by the first and second layers of water-resistant material;
- the first and second bus bars are adapted for coupling to a power source for powering the heating element; and
- the first and second bus bars comprise one of: a metal wire, a metal foil and a conductive ink.
35. The blanket of claim 34, wherein the layer of thermal insulation extends over the first and second bus bars.
36. An electric warming blanket, comprising:
- a flexible heater including a first lateral edge and a second lateral edge opposite the first lateral edge;
- a flexible shell enveloping the flexible heater, to form a substantially hermetically sealed space for the flexible heater, and extending beyond both the first and second lateral edges of the heater;
- at least one first stiffening member supported by the flexible shell beyond the first lateral edge of the heater; and
- at least one second stiffening member supported by the flexible shell beyond the second lateral edges of the heater.
37. The blanket of claim 36, wherein the flexible heater comprises a conductive fabric.
38. The blanket of claim 36, wherein the flexible heater comprises carbon.
39. The blanket of claim 36, wherein the flexible heater comprises a nonconductive layer coated with a conductive material.
40. The blanket of claim 39, wherein the nonconductive layer of the heater comprises a woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
41. The blanket of claim 39, wherein the nonconductive layer of the heater comprises a non-woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
42. The blanket of claim 39, wherein the non-conductive layer of the heater comprises a non-woven cellulose material and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
43. The blanket of claim 36, wherein each of the at least one first and the at least one second stiffening members comprise a polymeric material.
44. The blanket of claim 36, wherein each of the at least one first and the at least one second stiffening members extend along a length of the heater.
45. The blanket of claim 44, wherein each of the at least one first and the at least one second stiffening members comprise a pair of stiffening members.
46. The blanket of claim 45, wherein each pair of more than one pair of stiffening members is separated by a flexible gap along the length of the heater.
47. The blanket of claim 36, wherein the flexible shell comprises a first layer of water resistant material coupled to a second layer of water resistant material about a perimeter of the heater and about at least a portion of a perimeter of each of the at least one first stiffening member and the at least one second stiffening member.
48. The blanket of claim 36, further comprising:
- a first conductive bus bar coupled to the heater and extending alongside the first lateral edge of the heater; and
- a second conductive bus bar coupled to the heater and extending alongside a second lateral edge of the heater;
- wherein the first and second bus bars are contained in the substantially hermetically sealed space formed by the flexible shell;
- the first and second bus bars are adapted for coupling to a power source for powering the heater; and
- the first and second bus bars comprise one of: a metal wire, a metal foil and a conductive ink.
49. An electric warming blanket, comprising:
- a flexible heater including a first lateral edge and a second lateral edge opposite the first lateral edge;
- a first conductive bus bar coupled to the heater and extending alongside the first lateral edge of the heater;
- a second conductive bus bar coupled to the heater and extending alongside the second lateral edge of the heater;
- a temperature sensor coupled to the heater at a location between the first and second bus bars where the heater will be in conductive contact with a body when the blanket is draped over the body;
- the temperature sensor providing input to a temperature controller, the controller adapted to control a supply of power to the first and second bus bars, the supply of power being based on a sensed temperature from the temperature sensor; and
- at least one super over-temperature sensor coupled to the heater between the first and second bus bars;
- the at least one super over-temperature sensor adapted to interrupt the supply of power to the first and second bus bars when a temperature sensed by the at least one super over-temperature sensor exceeds a prescribed temperature.
50. The blanket of claim 49, further comprising an over-temperature sensor coupled to the heater in proximity to the temperature sensor, the over-temperature sensor providing redundant input to the temperature controller.
51. The blanket of claim 49, further comprising a flexible shell enveloping the flexible heater, to form a substantially hermetically sealed space for the flexible heater, the first and second bus bars, the temperature sensor and the at least one super-over temperature sensor.
52. The blanket of claim 49, wherein the at least one super-over temperature sensor comprises a plurality of super over-temperature sensors wired in series with one another.
53. The blanket of claim 52, wherein a first portion of the plurality of super over-temperature sensors is disposed in proximity to the first bus bar and a second portion of the plurality of super over-temperature sensors is disposed in proximity to the second bus bar.
54. The blanket of claim 49, wherein the at least one super-over temperature sensor is disposed in proximity to one of the first and second bus bars.
55. The blanket of claim 49, wherein the heater comprises carbon.
56. The blanket of claim 49, wherein the heater comprises a nonconductive layer coated with a conductive material.
57. The blanket of claim 56, wherein the nonconductive layer of the heater comprises a woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
58. The blanket of claim 56, wherein the nonconductive layer of the heater comprises a non-woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
59. The blanket of claim 56, wherein the non-conductive layer of the heater comprises a non-woven cellulose material and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
60. The blanket of claim 49, wherein the at least one super over-temperature sensor interrupts the supply of power by opening a power circuit that couples the supply of power to the first and second bus bars.
61. The blanket of claim 49, wherein the at least one super over-temperature sensor interrupts the supply of power by increasing in resistance.
62. The blanket of claim 49, wherein the at least one super over-temperature sensor is part of an over-temperature circuit adapted to indirectly interrupt the supply of power.
63. The blanket of claim 49, wherein the at least one super over-temperature sensor is part of a power circuit which is adapted to directly interrupt the supply of power.
64. The blanket of claim 49, wherein the prescribed temperature is in a range from approximately 45° C. to approximately 60° C.
65. The blanket of claim 49, wherein the first and second bus bars comprise one of: a metal wire, a metal foil and a conductive ink.
Type: Application
Filed: Sep 29, 2006
Publication Date: Mar 29, 2007
Inventors: Scott Augustine (Bloomington, MN), Randall Arnold (Minnetonka, MN), Ryan Augustine (Minneapolis, MN), Rudolf Deibel (Eden Prairie, MN), Scott Entenman (St. Paul, MN), Gordon Lawrence (Minneapolis, MN), Keith Leland (Medina, MN), Thomas Neils (Minneapolis, MN)
Application Number: 11/537,199
International Classification: H05B 3/54 (20060101); H05B 3/34 (20060101);