U.S. patent application number 11/537199 was filed with the patent office on 2007-03-29 for novel designs for an electric warming blanket including a flexible heater.
Invention is credited to Randall C. Arnold, Ryan S. Augustine, Scott D. Augustine, Rudolf A. Deibel, Scott A. Entenman, Gordon D. Lawrence, Keith J. Leland, Thomas F. Neils.
Application Number | 20070068931 11/537199 |
Document ID | / |
Family ID | 37460232 |
Filed Date | 2007-03-29 |
United States Patent
Application |
20070068931 |
Kind Code |
A1 |
Augustine; Scott D. ; et
al. |
March 29, 2007 |
NOVEL DESIGNS FOR AN ELECTRIC WARMING BLANKET INCLUDING A FLEXIBLE
HEATER
Abstract
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.
Inventors: |
Augustine; Scott D.;
(Bloomington, MN) ; Arnold; Randall C.;
(Minnetonka, MN) ; Augustine; Ryan S.;
(Minneapolis, MN) ; Deibel; Rudolf A.; (Eden
Prairie, MN) ; Entenman; Scott A.; (St. Paul, MN)
; Lawrence; Gordon D.; (Minneapolis, MN) ; Leland;
Keith J.; (Medina, MN) ; Neils; Thomas F.;
(Minneapolis, MN) |
Correspondence
Address: |
INTELLECTUAL PROPERTY GROUP;FREDRIKSON & BYRON, P.A.
200 SOUTH SIXTH STREET
SUITE 4000
MINNEAPOLIS
MN
55402
US
|
Family ID: |
37460232 |
Appl. No.: |
11/537199 |
Filed: |
September 29, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60825573 |
Sep 13, 2006 |
|
|
|
60722106 |
Sep 29, 2005 |
|
|
|
60722246 |
Sep 29, 2005 |
|
|
|
Current U.S.
Class: |
219/549 |
Current CPC
Class: |
A61F 2007/0001 20130101;
H05B 2203/016 20130101; A61B 2017/00084 20130101; A61B 46/00
20160201; H05B 3/342 20130101; A61F 2007/0071 20130101; H05B
2203/011 20130101; A61F 7/007 20130101; A61B 46/27 20160201; A61F
2007/0086 20130101; A61F 2007/0257 20130101; H05B 2203/017
20130101 |
Class at
Publication: |
219/549 |
International
Class: |
H05B 3/54 20060101
H05B003/54; H05B 3/34 20060101 H05B003/34 |
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.degree. C. to approximately
60.degree. 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.
Description
PRIORITY CLAIM
[0001] 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 APPLICATIONS
[0002] The 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 FIELD
[0003] The present invention is related to electric heating or
warming blankets or pads and more particularly to those including
flexible heating elements.
BACKGROUND
[0004] It 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.
[0005] 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.
[0006] 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.degree. 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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 DRAWINGS
[0012] The 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.
[0013] FIG. 1A is a plan view of a flexible heating blanket
subassembly for a heating blanket, according to some embodiments of
the present invention.
[0014] FIGS. 1B-C are end views of two embodiments of the
subassembly shown in FIG. 1A.
[0015] FIG. 1D is a schematic showing a blanket including the
subassembly of FIG. 1A draped over a body.
[0016] FIG. 2A is a top plan view of a heating element assembly,
according to some embodiments of the present invention, which may
be incorporated in the blanket shown in FIG. 3A.
[0017] FIG. 2B is a section view through section line A-A of FIG.
2A.
[0018] FIG. 2C is an enlarged plan view and corresponding end view
schematic of a portion of the assembly shown in FIG. 2A, according
to some embodiments of the present invention.
[0019] FIG. 2D is an enlarged view of a portion of the assembly
shown in FIG. 2A, according to some embodiments of the present
invention.
[0020] FIG. 3A is a top plan view, including partial cut-away
views, of a lower body heating blanket, according to some
embodiments of the present invention.
[0021] FIG. 3B is a schematic side view of the blanket of FIG. 3A
draped over a lower body portion of a patient.
[0022] FIG. 3C is a top plan view of a heating element assembly,
which may be incorporated in the blanket shown in FIG. 3A.
[0023] FIG. 3D is an cross-section view through section line D-D of
FIG. 3C.
[0024] FIG. 4A is a plan view of flexible heating element,
according to some alternate embodiments of the present
invention.
[0025] FIG. 4B is a top plan view, including a partial cut-away
view, of a heating element assembly, according to some embodiments
of the present invention, which may be incorporated in the blanket
shown in FIG. 4C.
[0026] FIG. 4C is a top plan view, including a partial cut-away
view, of an upper body heating blanket, according to some
embodiments of the present invention.
[0027] FIG. 4D is a schematic end view of the blanket of FIG. 4B
draped over an upper body portion of a patient.
DETAILED DESCRIPTION
[0028] 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.
[0029] FIG. 1A is a plan view of a flexible heating blanket
subassembly 100, according to some embodiments of the present
invention; and FOGS. 1B-C are end views of two embodiments of the
subassembly shown in FIG. 1A. FIG. 1A illustrates a flexible
sheet-like heating element or heater 10 of subassembly 100
including a first end 101, a second end 102, a first lateral
portion 11 extending between ends 101, 102, and a second lateral
portion 12, opposite first lateral portion 11, also extending
between ends 101, 102. According to preferred embodiments of the
present invention, heating element 10 comprises a conductive fabric
or a fabric incorporating closely spaced conductive elements such
that heater 10 has a substantially uniform watt density output,
preferably less than approximately 0.5 watts/sq. inch, and more
preferably between approximately 0.2 and approximately 0.4
watts/sq. inch, across a surface area, of one or both sides 13, 14
(FIGS. 1B-C), the surface area including and extending between
lateral portions 11, 12 of heater 10. Some examples of conductive
fabrics which may be employed by embodiments of the present
invention include, without limitation, carbon fiber fabrics,
fabrics made from carbonized fibers, woven or non-woven
non-conductive substrates coated with a conductive material, for
example, polypyrrole, carbonized ink, or metalized ink.
[0030] FIG. 1A further illustrates subassembly 100 including two
bus bars 15 coupled to heater 10 for powering heater 10; each bar
15 is shown extending alongside opposing lateral portions 11, 12,
between first and second ends 101, 102. With reference to FIG. 1B,
according to some embodiments, bus bars 15 are coupled to heating
element 10 within folds of opposing wrapped perimeter edges 108 of
heater 10 by a stitched coupling 145, for example, formed with
conductive thread such as silver-coated polyester or nylon thread
(Marktek Inc., Chesterfield, Mo.), extending through edges 108 of
heater 10, bars 15, and again through heater 10 on opposite side of
bars 15. According to alternate embodiments heater 10 is not folded
over bus bars 15 as shown. Alternative threads or yarns employed by
embodiments of the present invention may be made of other polymeric
or natural fibers coated with other electrically conductive
materials; in addition, nickel, gold, platinum and various
conductive polymers can be used to make conductive threads. Metal
threads such as stainless steel, copper or nickel could also be
used for this application. According to an exemplary embodiment,
bars 15 are comprised of flattened tubes of braided wires, such as
are known to those skilled in the art, for example, a flat braided
silver coated copper wire, and may thus accommodate the thread
extending therethrough, passing through openings between the
braided wires thereof. In addition such bars are flexible to
enhance the flexibility of blanket subassembly 100. According to
alternate embodiments, bus bars 15 can be a conductive foil or
wire, flattened braided wires not formed in tubes, an embroidery of
conductive thread, or a printing of conductive ink. Preferably, bus
bars 15 are each a flat braided silver-coated copper wire material,
since a silver coating has shown superior durability with repeated
flexion, as compared to tin-coated wire, for example, and may be
less susceptible to oxidative interaction with a polypyrrole
coating of heater 10 according to an embodiment described below.
Additionally, an oxidative potential, related to dissimilar metals
in contact with one another is reduced if a silver-coated thread is
used for stitched coupling 145 of a silver-coated bus bar 15.
[0031] 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/m.sup.2 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)=I.sup.2(Amps).times.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.
[0032] 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 FIG. 1D, heating element 10 may be draped over a
body 16 such that lateral portions 11, 12 do not contact side
surfaces of body 16; the mechanism of heat transfer between
portions 11, 12 and body 16, as illustrated in FIG. 1D, is
primarily radiant with some convection.
[0033] 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 FIG. 1D, an insulating air gap exists between the
body and those portions, so that the heat is not drawn off those
portions as easily. Therefore, those portions of heating element 10
not in conductive contact with the body will gain in temperature,
since heat is not transferred as efficiently from these portions as
from those in conductive contact with the body. The
`non-contacting` portions will reach a higher equilibrium
temperature than that of the `contacting` portions, when the
radiant and convective heat loss equal the constant heat production
through heating element 10. Although radiant and convective heat
transfer are more efficient at higher heater temperatures, the laws
of thermodynamics dictate that as long as there is a uniform
watt-density of heat production, even at the higher temperature,
the radiant and convective heat transfer from a blanket of this
construction will result in a lower heat flux to the skin than the
heat flux caused by the conductive heat transfer at the
`contacting` portions at the lower temperature. Even though the
temperature is higher, the watt-density is uniform and, since the
radiant and convective heat transfer are less efficient than
conductive heat transfer, the `non-contacting` portions must have a
lower heat flux. Therefore, by controlling the `contacting`
portions to a safe temperature, for example, via a temperature
sensor 121 coupled to heating element 10 in a location where
element 10 will be in conductive contact with the body, as
illustrated in FIG. 1D, the `non-contacting` portions, for example,
lateral portions 11, 12, will also be operating at a safe
temperature because of the less efficient radiant and convective
heat transfer. According to preferred embodiments, heating element
10 comprises a conductive fabric having a relatively small thermal
mass so that when a portion of the heater that is operating at the
higher temperature is touched, suddenly converting a
`non-contacting` portion into a `contacting` portion, that portion
will cool almost instantly to the lower operating temperature.
[0034] 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.degree. C. 42.degree.
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.degree. C. in order to achieve a
temperature of about 41-42.degree. 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
FIGS. 3A and 4C. With further reference to FIG. 1D, flaps 125 are
shown extending laterally from either side of heating element 10 in
order to enclose the sides of body 16 thereby preventing heat loss;
according to preferred embodiments of the present invention, flaps
125 are not heated and thus provide no thermal injury risk to body
if they were to be tucked beneath sides of body 16.
[0035] Referring now to the end view of FIG. 1C, an alternate
embodiment to that shown in FIG. 1B is presented. FIG. 1C
illustrates subassembly 100 wherein insulating members 18, for
example, fiberglass material strips having an optional PTFE coating
and a thickness of approximately 0.003 inch, extend between bus
bars 15 and heating element 10 at each stitched coupling 145, so
that electrical contact points between bars 15 and heating element
10 are solely defined by the conductive thread of stitched
couplings 145.
[0036] FIG. 2A is a top plan view of a heating element assembly
250, according to some embodiments of the present invention, which
may be incorporated by blanket 200, which is shown in FIG. 3A and
further described below. FIG. 2B is a section view through section
line A-A of FIG. 2A. FIGS. 2A-B illustrate a temperature sensor
assembly 421 assembled on side 14 of heater 10, and heater 10
overlaid on both sides 13, 14 with an electrically insulating layer
210, preferably formed of a flexible non-woven high loft fibrous
material, for example, 1.5 OSY (ounces per square yard) nylon,
which is preferably laminated to sides 13, 14 with a hotmelt
laminating adhesive. In some embodiments, the adhesive is applied
over the entire interfaces between layer 210 and heater 10. Other
examples of suitable materials for layer 210 include, without
limitation, polymeric foam, a woven fabric, a relatively thin
plastic film, cotton, and a non-flammable material, such as
fiberglass or treated cotton. According to preferred embodiments,
overlaid layers 210, without compromising the flexibility of
heating assembly 250, prevent electrical shorting of one portion of
heater 10 with another portion of heater 10 if heater 10 is folded
over onto itself. Because, according to preferred embodiments,
heating element assembly 250 will be enclosed within a relatively
durable and waterproof shell, for example shell 20 shown with
dashed lines in FIG. 2B, and will be powered by a relatively low
voltage (approximately 48V). Layers 210 may even be porous in
nature to further maintain the desired flexibility of assembly
250.
[0037] FIG. 2C is an enlarged plan view and a corresponding end
view schematic showing some details of the corner of assembly 250
that is circled in FIG. 2A, according to some embodiments. FIG. 2C
is representative of each corner of assembly 250. FIG. 2C
illustrates insulating layer 210 disposed over side 14 of heating
element and extending beneath bus bar 15, optional electrical
insulating member 18, and layer 210 disposed over side 13 of heater
10 and terminated adjacent bus bar 15 within lateral portion 12 so
that threads of conductive stitching 145 securing bus bars 15 to
heater 10 electrically contact heater 10 along side 13 of heater
10. FIG. 2C further illustrates two rows of conductive stitching
145 coupling bus bar 15 to heater 10, and bus bar 15 and insulating
member 18 extending past end 102; a backtack securing stitching 145
may be approximately 0.375 inches long and also extends beyond end
102.
[0038] FIG. 2A further illustrates junctions 50 coupling leads 205
to each bus bar 15, and another lead 221 coupled to and extending
from temperature sensor assembly 421; each of leads 205, 221 extend
over insulating layer 210 and into an electrical connector housing
225 containing a connector 23, which will be described in greater
detail below, in conjunction with FIGS. 3A-C. FIG. 2D is an
enlarged view of junction 50, which is circled in FIG. 2A,
according to some embodiments of the present invention. FIG. 2D
illustrates junction 50 including a conductive insert 55 which has
been secured to bus bar 15, for example, by inserting insert 55
through a side wall of bus bar 15 and into an inner diameter
thereof, the bus bar 15 of the illustrated embodiment being formed
by a braided wire tube so that an opening between the wires may be
formed for access to the inner diameter. Insert 55 may be secured
to bus bar 15 by compressing tubular bus bar 15 around insert 55
and further by stitching 145 that couples bus bar 15 to heating
element 10. FIG. 2D further illustrates lead 205 coupled to insert
55, for example, via soldering, and an insulating tube and strain
relief 54, for example, a polymer shrink tube, surrounding the
coupling between lead 205 and insert 55.
[0039] Returning now to FIG. 2B, temperature sensor assembly 421
will be described in greater detail. FIG. 2B illustrates assembly
421 including a substrate 211, for example, of polyimide (Kapton),
on which a temperature sensor 21, for example, a surface mount chip
thermistor (such as a Panasonic ERT-J1VG103FA: 10K, 1% chip
thermistor), is mounted; a heat spreader 212, for example, a copper
or aluminum foil, is mounted to an opposite side of substrate 211.
Temperature sensor assembly 421 may be bonded to layer 210 with an
adhesive layer 213, for example, hotmelt EVA. Some alternate
embodiments of the present invention address a non-uniform
resistance across a surface area of element 10 by employing a
distributed temperature sensor, for example, a resistance
temperature detector (RTD) laid out in flat plane across a surface
of heating element 10, or by employing an infrared temperature
measurement device positioned to receive thermal radiation from a
given area of heating element 10. An additional alternate
embodiment is contemplated in which an array of temperature sensors
are positioned over the surface of heating element 10, being spaced
apart so as to collect temperature readings which may be averaged
to account for resistance variance.
[0040] 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.
[0041] According to some embodiments of the present invention, for
example as illustrated in FIG. 2A, super over-temperature sensors
41 are incorporated to detect overheating of areas of assembly 250
susceptible to rucking, that is areas, for example, lateral
portions 11, 12, where assembly 250 is most likely to be folded
over on itself, either inadvertently or on purpose to gain access
to a portion of a patient disposed beneath a blanket including
assembly 250. An area of assembly 250 which is beneath the
folded-over portion of assembly 250, and not in close proximity to
sensor assembly 421, can become significantly warmer due to the
additional thermal insulation provided by the folded-over portion
that goes undetected by sensor 21. According to preferred
embodiments, sensors 41 are wired in series, as illustrated in FIG.
2A. Super over-temperature sensors 41 may be set to open, or
significantly increase resistance in, a circuit, for example, the
over-temperature circuit, thereby activating an alarm and/or
cutting power to heater 10, at prescribed temperatures that are
significantly above the normal operating range, for example,
temperatures between approximately 45.degree. C. and approximately
60.degree. C. Alternately, sensors 41 may be part of the bus bar
power circuit, in which case sensors 41 directly shut down power to
heater 10 when in an open condition or add sufficient resistance
when in a high resistance condition to substantially reduce heating
of heater 10.
[0042] FIG. 3A is a top plan view, including partial cut-away
views, of a lower body heating blanket 200, according to some
embodiments of the present invention, which may be used to keep a
patient warm during surgery. FIG. 3A illustrates blanket 200
including heating element assembly 250 covered by flexible shell
20; shell 20 protects and isolates assembly 250 from an external
environment of blanket 200 and may further protect a patient
disposed beneath blanket 200 from electrical shock hazards.
According to preferred embodiments of the present invention, shell
20 is waterproof to prevent fluids, for example, bodily fluids, IV
fluids, or cleaning fluids, from contacting assembly 250, and may
further include an anti-microbial element, for example, being a
SILVERion.TM. antimicrobial fabric available from Domestic Fabrics
Corporation. According to the illustrated embodiment, blanket 200
further includes a layer of thermal insulation 201 extending over a
top side (corresponding to side 14 of heater 10) of assembly 250;
layer 201 may or may not be bonded to a surface of assembly 250.
Layer 201 may serve to prevent heat loss away from a body disposed
on the opposite side of blanket 200, particularly if a heat sink
comes into contact with the top side of blanket 200. FIG. 3C
illustrates insulation 201 extending over an entire surface of side
14 of heater 10 and over sensor assembly 421. According to the
illustrated embodiment, layer 201 is secured to heating element
assembly 250 to form an assembly 250', as will be described in
greater detail below. According to an exemplary embodiment of the
present invention, insulating layer 201 comprises a polymer foam,
for example, a 1 pound density 30 ILD urethane foam, which has a
thickness between approximately 1/8.sup.th inch and approximately
3/4.sup.th inch. According to an alternate embodiment, layer 201 is
formed of a high loft fibrous polymeric non-woven material.
[0043] FIG. 3A further illustrates shell 20 forming flaps 25
extending laterally from either side of assembly 250 and a foot
drape 26 extending longitudinally from assembly 250. According to
exemplary embodiments of the present invention, a length of
assembly 250 is either approximately 28 inches or approximately 48
inches, the shorter length providing adequate coverage for smaller
patients or a smaller portion of an average adult patient. FIG. 3B
is a schematic side view of blanket 200 draped over a lower body
portion of a patient. With reference to FIG. 3B it may be
appreciated that flaps 25, extending down on either side of the
patient, and foot drape 26, being folded under and secured by
reversible fasteners 29 (FIG. 3A) to form a pocket about the feet
of the patient, together effectively enclose the lower body portion
of the patient to prevent heat loss. With further reference to FIG.
3B, it may also be appreciated that neither shell 20 nor insulation
layer 201 add appreciable stiffness to heater 10 so that blanket
200 conforms nicely to the contour of the patient's lower body.
With reference to FIG. 2A, in conjunction with FIG. 3B, it may be
appreciated that temperature sensor assembly 421 is located on
assembly 250 so that, when blanket 200 including assembly 250 is
draped over the lower body of the patient, the area of heater 10
surrounding sensor assembly 421 will be in conductive contact with
one of the legs of the patient in order to maintain a safe
temperature distribution across heater 10.
[0044] 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 FIG. 3A) that extends about a perimeter edge 2000 of
blanket 200, and within perimeter edge 2000 to form zones, or
pockets, where a gap exists between the two sheets. According to an
exemplary embodiment of the present invention, shell 20 comprises a
nylon fabric having an overlay of polyurethane coating to provide
waterproofing; the coating is on at least an inner surface of each
of the two sheets, further facilitating a heat seal between the two
sheets, for example, along seal zone 22, according to preferred
embodiments. It should be noted that, according to alternate
embodiments of the present invention, a covering for heating
assemblies, such as heating assembly 250, may be removable and,
thus, include a reversible closure facilitating removal of a
heating assembly therefrom and insertion of the same or another
heating assembly therein.
[0045] FIG. 3A further illustrates flaps 25 including zones where
there are gaps between the sheets to enclose weighting members,
which are shown as relatively flat plastic slabs 255. Alternately
flaps 25 can be weighted by attaching weighting members to exterior
surfaces thereof. Examples of other suitable weighting members
include but are not limited to a metal chain, a metal spring, lead
shot, plastic rods and sand. The weighting of flaps 25 causes flaps
25 to hang down in order to provide a more secure air seal about
the patient. The weighting members may further discourage a
clinician from tucking flaps 25 under the patient as a safety
feature to help to prevent a portion of the blanket containing
heater 10 from coming into relatively high pressure contact with
the patient, where it could cause serious burns; as such, the
weighting members are relatively stiff and/or form a lump at the
outer edge of flaps 25. Relatively stiff flap weighting members
255, for example, batten-like flat plastic slabs 255, by extending
along the length of assembly 250, may further prevent inadvertent
rucking of blanket 200, that is, the folding of blanket 200 over on
itself, which could lead to over-heating of a portion of heater 10,
as previously described. However, with reference to FIG. 3A, seal
zone 22 extending between members 255 along each flap 25 can
predetermine a folding location; the predetermined folding location
can prevent overheating (due to the location of sensor assembly
421) or can dictate the placement of super over-temperature sensors
41, as previously described.
[0046] FIG. 3C is a top plan view, including partial cut-away
views, of heating element assembly 250', which may be incorporated
in blanket 200; and FIG. 3D is a cross-section view through section
line D-D of FIG. 3C. FIGS. 3C-D illustrates heating element
assembly 250' including heater 10 overlaid with electrical
insulation 210 on both sides 13, 14 and thermal insulation layer
201 extending over the top side 14 thereof (dashed lines show leads
and sensor assembly beneath layer 201). According to the
illustrated embodiment, layer 201 is inserted beneath a portion of
each insulating member 18, each which has been folded over the
respective bus bar 15, for example as illustrated by arrow B in
FIG. 1C, and then held in place by a respective row of
non-conductive stitching 345 that extends through member 18, layer
201 and heater 10. Although not shown, it should be appreciated
that layer 201 may further extend over bus bars 15. Although layer
210 is shown extending beneath layer 201 on side 14 of heating
element, according to alternate embodiments, layer 201
independently performs as a thermal and electrical insulation so
that layer 210 is not required on side 14 of heater 10. FIG. 3C
further illustrates, with longitudinally extending dashed lines, a
plurality of optional slits in layer 201, which may extend
partially or completely through layer 201, in order to increase the
flexibility of assembly 250'. Such slits are desirable if a
thickness of layer 201 is such that it prevents blanket 200 from
draping effectively about a patient; the optional slits are
preferably formed, for example, extending only partially through
layer 201 starting from an upper surface thereof, to allow bending
of blanket 200 about a patient and to prevent bending of blanket
200 in the opposition direction.
[0047] Returning now to FIG. 2A, to be referenced in conjunction
with FIGS. 3A-C, connector housing 225 and connector 23 will be
described in greater detail. According to certain embodiments,
housing 225 is an injection molded thermoplastic, for example, PVC,
and may be coupled to assembly 250 by being stitched into place,
over insulating layer 210. FIG. 2A shows housing 225 including a
flange 253 through which such stitching can extend. With reference
to FIGS. 3A-B, it can be seen that connector 23 protrudes from
shell 20 of blanket 200 so that an extension cable 330 may couple
bus bars 15 to a power source 234, and temperature sensor assembly
421 to a temperature controller 232, both shown incorporated into a
console 333. In certain embodiments, power source 234 supplies a
pulse-width-modulated voltage to bus bars 15. The controller 232
may function to interrupt such power supply (e.g., in an
over-temperature condition) or to modify the duty cycle to control
the heating element temperature. According to the illustrated
embodiment, a surface 252 of flange 253 of housing 225 protrudes
through a hole formed in thermal insulating layer 201 (FIG. 3C) so
that a seal 202 (FIG. 3A) may be formed, for example, by adhesive
bonding and/or heat sealing, between an inner surface of shell 20
and surface 252.
[0048] 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 FIG. 3C, each strip
271 extending longitudinally from and alongside respective ends
101, 102 of heating element 10 and being coupled thereto by a
respective row of non-conductive stitching 354. Strips 271 may
extend over layer 201 or beneath heating element 10. Strips 217
preferably extend over conductive stitching 145 on side 13 of
heating element 10, as shown, to provide a layer of insulation that
can prevent shorting between portions of side 13 of heating element
10 if element 10 were to fold over on itself along rows of
conductive stitching 145 that couple bus bars 15 to heating element
10; however, strips 217 may alternately extend over insulating
member 18 on the opposite side of heating element 10. According to
the illustrated embodiment, securing strips 217 and 271 are made of
a polymer material, for example polyurethane, so that they may be
heat sealed between the sheets of shell 20 in corresponding areas
of heat seal zone 22 in order to secure heating element assembly
250' within the corresponding gap between the two sheets of shell
20 (FIG. 3A).
[0049] FIG. 4A is a plan view of flexible heating element 30,
according to some alternate embodiments of the present invention.
Heating element 30 is similar in nature to previously described
embodiments of heating element 10, being comprised of a conductive
fabric, or a fabric incorporating closely spaced conductive
elements, for a substantially uniform watt density output,
preferably less than approximately 0.5 watts/sq. inch. While a
shape of the surface area of heating element 10 is suited for a
lower body blanket, such as blanket 200, that would cover a lower
abdomen and legs of a patient (FIG. 3B) undergoing upper body
surgery, the shape of a surface area of heating element 30 is
suited for an upper body heating blanket, for example, blanket 300
shown in FIG. 4C, that would cover outstretched arms and a chest
area of a patient undergoing lower body surgery (FIG. 4D).
According to an exemplary embodiment for an adult upper body
heating blanket, a distance between a first end 301 of element 30
and a second end 302 of element 30 is between about 70 and 80
inches, while a distance between a first lateral edge 311 and a
second lateral edge 312 is about 7 to 10 inches. With reference to
FIG. 4B, which shows heating element 30 incorporated into a heating
element assembly 450, it can be seen that bus bars 15 are coupled
to element 30 alongside respective lateral edges 311, 312 (FIG.
4A). For the narrower spacing between bus bars 15, compared with
that for heating element 10 incorporated in blanket 200, element
30, in order to have the desired watt density output, should be
comprised of a conductive fabric having a higher resistance than
the examples previously recited for heating element 10, for
example, on the order of 100 ohms per square, measured with a four
point probe. An example of a conductive fabric meeting this
resistance requirement is a woven silk-like polyester, for example,
known as Pongee, being 100% coated with polypyrrole.
[0050] FIG. 4B is a top plan view, including partial cut-away
views, of heating element assembly 450, according to some
embodiments of the present invention, which may be incorporated in
blanket 300 shown in FIG. 4C. FIG. 4B illustrates assembly 450
having a configuration similar to that of assembly 250', which is
illustrated in FIGS. 3C-D. According to the embodiment illustrated
in FIG. 4B, temperature sensor assembly 421 is coupled to heating
element 30 at a location where element 30, when incorporated in an
upper body heating blanket, for example, blanket 300, would come
into conductive contact with the chest of a patient, for example as
illustrated in FIG. 4D, in order to maintain a safe temperature
distribution across element 30; bus bar junctions 50 and connector
housing 225 are located in proximity to sensor assembly 421 in
order to keep a length of leads 205 and 221 to a minimum. With
reference back to FIGS. 3C-D, in conjunction with FIG. 4B, an
electrical insulating layer 310 of assembly 450 corresponds to
insulating layers 210 of assembly 250', a thermal insulating layer
301 of assembly 450 corresponds to layer 201 of assembly 250', and
securing strips 317 and 371 of assembly 450 generally correspond to
strips 217 and 271, respectively, of assembly 250'.
[0051] FIG. 4C is a top plan view, including partial cut-away
views, of upper body heating blanket 300, according to some
embodiments of the present invention. FIG. 4C illustrates blanket
300 including heating element assembly 450 covered by a flexible
shell 40; shell 40 protects and isolates assembly 450 from an
external environment of blanket 300 and may further protect a
patient disposed beneath blanket 300 from electrical shock hazards.
According to preferred embodiments, shell 40 is similar to shell 20
of blanket 200 in that shell 40 is relatively durable and
waterproof and may further include an antimicrobial element or
layer extending over an exterior surface thereof. According to the
illustrated embodiment, shell 40, like shell 20, includes top and
bottom sheets; the sheets extend over either side of assembly 450
and are coupled together along a seal zone 32 that extends around a
perimeter edge 4000 and within edge 4000 to form various zones, or
pockets, where gaps exist between the two sheets. The sheets of
shell 40 may be heat sealed together along zone 32, as previously
described for the sheets of shell 20. With reference to FIG. 4B,
securing strips 317 may be heat sealed between the sheets of shell
40 in corresponding areas of seal zone 32, on either side of a
central narrowed portion 39 of blanket 300, in order to secure
heating element assembly 450 within the corresponding gap between
the two sheets of shell 40. According to an alternate embodiment,
for example, as shown with dashed lines in FIG. 4A, lateral edges
311, 312 of heating element 30 extend out to form securing edges 27
that each include slots or holes 207 extending therethrough so that
inner surfaces of sheets of shell 40 can contact one another to be
sealed together and thereby hold edges 27. It should be noted that
either of blankets 200, 300, according to alternate embodiments of
the present invention, may include more than one heating element
10, 30 and more than one assembly 250/250', 450.
[0052] With reference to FIG. 4C, it may be appreciated that
blanket 300 is symmetrical about a central axis 30 and about
another central axis, which is orthogonal to axis 30. FIG. 4C
illustrates shell 40 forming flaps 35A, 35B and 350, each of which
having a mirrored counterpart across central axis 30 and across the
central axis orthogonal to axis 30. According to the illustrated
embodiment, each of flaps 35A, B include weighting members 305,
which are similar to members 255 of blanket 200, and which may
stiffen flaps 35A,B (dashed lines indicate outlines of members 305
held between the sheets of cover 40 by surrounding areas of seal
zone 32).
[0053] FIG. 4C further illustrates straps 38, each extending
between respective flaps 35A-B. With reference to FIG. 4D, which is
a schematic end view of blanket 300 draped over an upper body
portion of a patient, it may be appreciated that flaps 35A-B and
350 extend downward to enclose the outstretched arms of the patient
in order to prevent heat loss and that straps 38 secure blanket 300
about the patient. Opposing straps 38 may be secured together with
reversible fasteners, examples of which include, without
limitation, magnetic fasteners, either embedded within straps 38 or
coupled to outer surfaces thereof, and mating hook-and-loop
fasteners attached to opposing straps 38. According to preferred
embodiments, portions of perimeter edge 4000 defining narrowed
portion 39, which extends across a chest of the patient, are either
rounded or padded to provide a softer interface with the patient's
chin if blanket 300 were to slip off the patient's chest toward the
patient's chin.
[0054] With further reference to FIG. 4D, it may also be
appreciated that, when blanket 300 is positioned over the patient,
each strap 38 is positioned in proximity to an elbow of the patient
so that either end portion of blanket 300, corresponding to each
pair of flaps 35A, may be temporarily folded back, as illustrated,
per arrow C, in order for a clinician to access the patient's arm,
for example, to insert or adjust an IV. According to some
embodiments of the present invention, super over-temperature
sensors, for example, sensors 41, previously described, are
included in blanket 300 being located according to the anticipated
folds, for example at general locations 410 illustrated in FIGS.
4B-C, in order to detect over-heating, which may occur if blanket
300 is folded over on itself, as illustrated in FIG. 4D, for too
long a time, and, particularly, if flaps 35A of folded-back portion
of blanket are allowed to extend downward as illustrated with the
dashed line in FIG. 4D. FIG. 4D further illustrates connector cord
330 plugged into connector 23 to couple heating element 30 and
temperature sensor assembly 421 of blanket 300 to control console
333.
[0055] 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.
* * * * *