U.S. patent application number 11/537189 was filed with the patent office on 2007-03-29 for temperature sensor assemblies for electric warming blankets.
Invention is credited to Scott D. Augustine, Scott A. Entenman, Gordon D. Lawrence, Keith J. Leland.
Application Number | 20070068928 11/537189 |
Document ID | / |
Family ID | 37460232 |
Filed Date | 2007-03-29 |
United States Patent
Application |
20070068928 |
Kind Code |
A1 |
Augustine; Scott D. ; et
al. |
March 29, 2007 |
TEMPERATURE SENSOR ASSEMBLIES FOR ELECTRIC WARMING BLANKETS
Abstract
An electric warming blanket for warming patients during surgery
and other medical procedures includes a flexible heater and a
temperature sensor assembly coupled thereto; a first layer of water
resistant material coupled to a second layer of water resistant
material, about a perimeter of the heater, forms a substantially
hermetically sealed space for the heater and the temperature sensor
assembly. The blanket may further include a thermal insulation
layer disposed between the temperature sensor assembly and the
first layer of water resistant material. The temperature sensor
assembly may provide input of an average temperature over a portion
of a surface area of the heater to a temperature controller, when
the heater and sensor assembly are coupled to the controller.
Inventors: |
Augustine; Scott D.;
(Bloomington, MN) ; Entenman; Scott A.; (St. Paul,
MN) ; Leland; Keith J.; (Medina, MN) ;
Lawrence; Gordon D.; (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.: |
11/537189 |
Filed: |
September 29, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
60825573 |
Sep 13, 2006 |
|
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|
60722106 |
Sep 29, 2005 |
|
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60722246 |
Sep 29, 2005 |
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Current U.S.
Class: |
219/528 |
Current CPC
Class: |
A61B 46/27 20160201;
A61B 46/00 20160201; A61F 2007/0001 20130101; A61F 2007/0086
20130101; H05B 2203/017 20130101; H05B 2203/011 20130101; A61F
2007/0257 20130101; A61B 2017/00084 20130101; A61F 2007/0071
20130101; H05B 3/342 20130101; A61F 7/007 20130101; H05B 2203/016
20130101 |
Class at
Publication: |
219/528 |
International
Class: |
H05B 3/34 20060101
H05B003/34; H05B 3/54 20060101 H05B003/54 |
Claims
1. An electric warming blanket for warming patients during surgery
and other medical procedures, comprising: a flexible heater having
a surface area and a substantially uniform watt density output
across the surface area when the heater is electrically powered; a
temperature sensor assembly coupled to the heater and providing
input of an average temperature over a portion of the surface area
of the heater to a temperature controller when the heater and the
sensor assembly are coupled to the controller; 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
temperature sensor assembly.
2. The blanket of claim 1, wherein the heater comprises a
conductive fabric.
3. The blanket of claim 1, wherein the heater comprises carbon.
4. The blanket of claim 1, wherein the heater comprises a
nonconductive layer coated with a conductive material.
5. The blanket of claim 4, wherein the nonconductive layer
comprises a woven polyester and the conductive material comprises
polypyrrole.
6. The blanket of claim 1, wherein the heater comprises a fabric
incorporating closely spaced conductive elements.
7. The blanket of claim 1, wherein the portion is disposed along
the surface area so at to be in conductive contact with the patient
when the blanket is placed over the patient to warm the
patient.
8. The blanket of claim 1, wherein the temperature sensor assembly
includes a temperature sensor coupled to a heat spreader, the heat
spreader extending over the portion of the surface area.
9. The blanket of claim 8, wherein the portion of the surface area
is no greater than approximately four square inches.
10. The blanket of claim of claim 8, wherein the heat spreader
comprises a metal foil.
11. The blanket of claim 1, wherein the temperature sensor assembly
includes a distributed temperature sensor comprising a resistance
temperature detector (RTD) laid out in a flat plane across the
portion of the surface area.
12. The blanket of claim 1, wherein the temperature sensor assembly
includes an array of temperature sensors spaced apart over the
portion of the surface area.
13. An electric warming blanket for warming patients during surgery
and other medical procedures, 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 heater is
electrically powered; a temperature sensor assembly coupled to the
first side of the heater; a first layer of water resistant material
disposed over the first side of the heater, being un-adhered
thereto, and forming a top surface of the blanket when the blanket
is placed over the patient; a second layer of water resistant
material disposed over the second side of the heater, being
un-adhered thereto, and forming a bottom surface of the blanket,
adjacent to the patient, when the blanket is placed over the
patient, 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 the temperature sensor; and a layer of thermal
insulation disposed between the temperature sensor assembly and the
first layer of water resistant material.
14. The blanket of claim 13, wherein the flexible heater comprises
a conductive fabric.
15. The blanket of claim 13, wherein the heater comprises
carbon.
16. The blanket of claim 13, wherein the heater comprises a
nonconductive layer coated with a conductive material.
17. The blanket of claim 16, wherein the nonconductive layer
comprises a woven polyester and the conductive material comprises
polypyrrole.
18. The blanket of claim 13, wherein the flexible heater comprises
a fabric incorporating closely spaced conductive elements.
19. The blanket of claim 13, wherein the layer of thermal
insulation comprises flexible polymeric foam.
20. The blanket of claim 13, wherein the layer of thermal
insulation comprises high loft fibrous polymeric non-woven
material.
21. The blanket of claim 13, wherein the layer of thermal
insulation comprises non-woven cellulose material.
22. The blanket of claim 13, wherein the layer of thermal
insulation comprises air.
23. An electric warming blanket for warming patients during surgery
and other medical procedures, comprising: a flexible heater having
a surface area and a substantially uniform watt density output
across the surface area when the heater is electrically powered;
and a temperature sensor assembly coupled to the heater, the sensor
assembly including a temperature sensor and a heat spreader, and
the heat spreader comprising a metal foil disposed between the
temperature sensor and the heater.
24. The blanket of claim 23, wherein the temperature sensor
comprises a surface mount chip thermistor.
25. The blanket of claim 23, wherein the heat spreader extends over
a portion of the surface area of the heater, the portion being no
greater than approximately four square inches.
26. The blanket of claim 23 wherein the heater spreader has a
thickness that is no greater than approximately 0.001 inch.
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) FLEXIBLE HEATING ELEMENT
CONSTRUCTION, Practitioner docket number 49278.2.15; 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 heating or warming
blankets or pads and more particularly to those including
electrical 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] To overcome the aforementioned problems with FAW, several
companies have developed electric warming blankets. However, there
is still a need for electrically heated blankets or pads that can
be used safely and effectively warm patients undergoing surgery or
other medical treatments. These blankets need to be flexible in
order to effectively drape over the patient (making excellent
contact for conductive heat transfer and maximizing the area of the
patient's skin receiving conductive as well as radiant heat
transfer), and should incorporate means for precise temperature
control.
[0008] Precise temperature control is important because non-uniform
heat distribution can occur within an electric warming blanket.
Unfortunately, many temperature sensors used to provide feedback to
a temperature controller do not dependably report an accurate
average temperature of the blanket because they sense temperature
from too small of an area. For example, if the temperature of a
measured location is cooler than the average blanket temperature,
the temperature sensor will cause the controller to deliver more
power to the heater and the resulting average temperature of the
heater will be higher than desired.
[0009] Further, an electric blanket can overheat if the temperature
sensor is thermally grounded to a cool object. This condition can
occur if a cool object such as a metal pan is placed on top of the
heater in the area of the temperature sensor. The sensor "feels"
cool and tells the temperature controller to deliver more power to
the heater.
[0010] Accordingly, there is a need for a blanket that utilizes a
temperature sensor that takes temperature measurements that are
representative of the average temperature of the blanket. Further,
there is a need for a blanket with a temperature sensor that will
not cause the blanket to overheat if a cool object is placed in
proximity to it. Various embodiments of the invention described
herein solve one or more of the problems discussed above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] 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.
[0012] FIG. 1A is a plan view of a flexible heating blanket
subassembly for a heating blanket, according to some embodiments of
the present invention.
[0013] FIGS. 1B-C are end views of two embodiments of the
subassembly shown in FIG. 1A.
[0014] FIG. 1D is a schematic showing a blanket including the
subassembly of FIG. 1A draped over a body.
[0015] 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.
[0016] FIG. 2B is a section view through section line A-A of FIG.
2A.
[0017] 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.
[0018] FIG. 2D is an enlarged view of a portion of the assembly
shown in FIG. 2A, according to some embodiments of the present
invention.
[0019] 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.
[0020] FIG. 3B is a schematic side view of the blanket of FIG. 3A
draped over a lower body portion of a patient.
[0021] FIG. 3C is a top plan view of a heating element assembly,
which may be incorporated in the blanket shown in FIG. 3A.
[0022] FIG. 3D is a cross-section view through section line D-D of
FIG. 3C.
[0023] FIG. 4A is a plan view of flexible heating element,
according to some alternate embodiments of the present
invention.
[0024] 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.
[0025] 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.
[0026] FIG. 4D is a schematic end view of the blanket of FIG. 4B
draped over an upper body portion of a patient.
DETAILED DESCRIPTION
[0027] 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.
[0028] FIG. 1A is a plan view of a flexible heating blanket
subassembly 100, according to some embodiments of the present
invention; and FIGS. 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, heater 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.
[0029] FIG. 1A further illustrates subassembly 100 including two
bus bars 15 coupled to heating element 10 for powering element 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 heating element 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 heating element 10, bars 15, and again through heating
element 10 on opposite side of bars 15. According to alternate
embodiments heating element 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 heating element 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.
[0030] 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 heater 10,
is directly related to heat generation according to the following
relationship: Q (Joules)=I.sup.2(Amps).times.R(Ohms)
[0031] 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, such as cotton or
fiberglass, and a relatively thin plastic film. 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. Heating element
assembly 250 may 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 heater 10
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 heating element 10 along side 13 of heating
element 10. FIG. 2C further illustrates two rows of conductive
stitching 145 coupling bus bar 15 to heating element 10, and bus
bar 15 and insulating member 18 extending past 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. 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: 10 K, 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,
for example, being bonded with a pressure sensitive adhesive;
substrate 211 is relatively thin, for example about 0.0005 inch
thick, so that heat transfer between heat spreader 212 and sensor
is not significantly impeded. Temperature sensor assembly 421 may
be bonded to layer 210 with an adhesive layer 213, for example,
hotmelt EVA. Although not shown, it should be noted that sensor
assembly 421 may be potted with a flexible electrically insulating
material, such as silicon or polyurethane.
[0040] According to the illustrated embodiment, heat spreader 212
is sized to contact an enlarged surface area so that a temperature
sensed by sensor 21 is more representative of an average
temperature over a region of heater 10 surrounding sensor 21, which
is positioned such that, when a heating blanket including heater 10
is placed over a body, the regions surrounding sensor 21 will be in
conductive contact with the body. As previously described, it is
desirable that a temperature of approximately 43.degree. C. be
maintained over a surface of heater 10 which is in conductive
contact with a body of a patient undergoing surgery. Other types of
heat spreaders, in addition to metallic foils, include metallic
meshes or screens, or an adhesive/epoxy filled with a thermally
conductive material.
[0041] Heat spreader 212 is a desirable component of a temperature
sensor assembly, according to some embodiments of the present
invention, since conductive fabrics employed by heating element 10,
such as those previously described, may not exhibit uniform
resistance across surface areas thereof. Heat spreader 212, having
a surface area that does not exceed approximately four square
inches, according to a preferred embodiment, may be effective in
averaging out relatively small scale spatial resistance variation,
for example, about 3% to 10% variability over less than about one
or two inches. Such a limitation on heat spreader 212 surface area
may be necessary so that heat spreader 212 does not become too
bulky, since the larger the surface area, the greater the thickness
of spreader 212 needed in order to maintain effective heat transfer
across spreader 212 and to sensor 21. In addition, if spreader 212
is too thick, a thermal mass of spreader 212 will cause spreader
212 to respond too slowly to changes in heat loss or gain by
heating element. According to an exemplary embodiment of the
present invention, spreader 212 has a surface area of no greater
than approximately four square inches and a thickness of no greater
than approximately 0.001 inch. 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 heater 10, or by employing an
infrared temperature measurement device positioned to receive
thermal radiation from a given area of heater 10. An additional
alternate embodiment is contemplated in which an array of
temperature sensors are positioned over the surface of heater 10,
being spaced apart so as to collect temperature readings which may
be averaged to account for resistance variance.
[0042] 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.
[0043] 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 heating element 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 heating element 10 when in an open condition or add
sufficient resistance when in a high resistance condition to
substantially reduce heating of element 10.
[0044] 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 heating element 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 heating element 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 alternate
embodiments layer 201 comprises any, or a combination of the
following: high loft fibrous polymeric non-woven material,
non-woven cellulose material, and air, for example, held within a
polymeric film bubble.
[0045] 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 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 heating element 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 element 10.
[0046] 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.
[0047] 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.
[0048] 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 heating element 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 heating element 10. 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 heating element 10.
[0049] 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.
[0050] 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 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).
[0051] 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). 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).
[0052] 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'.
[0053] 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 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.
[0054] 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).
[0055] 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.
[0056] 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.
[0057] 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.
* * * * *