Note: Descriptions are shown in the official language in which they were submitted.
2109431 :
- THERMISTOR ASSEMBLIES
AND METHODS FOR MAKING SAME
Background of the Invention
The present invention relates to sensor assemblies, for
example, to thermistor assemblies, and to methods for
making such sensor assemblies. More particularly, the
invention relates to sensor assemblies which are
electrically insulated with ovexcoatings which allow for
rapid sensor response to changes in the ~alue of the
parameter being sensed, and which are preferably
biocompatible so that the sensor assemblies can be used in
vivo for the treatment/diagnosis of medical patients.
Sensing elements which provide an electrical signal in
response to the value of the parameter being sensed often
are provided in a disassembled state. For example,
thermistors are often sold as basic units which include the
usual thermistor element, for example, a conventional
thermistor chip, wafer, bead or the li~e; a protective
coatingl often made o~ glass, hermetically sealed over the
thermistor element; and relatively short length, on the
order of about 1 inch~ electrically conductive lead wires
in electrical communication with the thermistor element and
which extend beyond the protective coating. In order to
effectively use such thermistor units, it is often
necessary to bond these lead wires to electrically
conductive extension wires in an elongated cord, which
extension wires are ultimately in electrical communication
with a remotely located temperature monitoring unit, which
may be of conventional design.
In assembling the thermistor/elongated cord combination,
it is often important that the connection between the lead
wires and the extension wires be electrically insulated,
for example, for reasons of safety and to protect the
integrity of the electrical signals being transmitted by
~5 these wires. In addition, it is often important that the
, . .~ .,, ,,, . , ~. ~ - ,
9 ~ 3 1
thermistor assembly be such that the included thermistor
have a fast or rapid response time, that is, that the
included thermistor be rapidly responsive to changes in the
temperature being sensed.
Further factors become important when the thermistor
assembly is to be used i~ vivo, for example, in the
presence of bodily fluids, such as blood. In such
applications,~ the thermistor assembly should preferably be
biocompatible, that is, should preferably be such as to
cause no substantial harm to the individual in whose body
it is placed and to remain substantially intact (maintain
substantial structural integrity) while in such
individual's body.
The thermistor assembly production operation itself
should be such as to provide reliable products, which'meet
relatively tight or high quality control requirements.
Thermistor assemblies have been produced by bonding the
thermistor's lead wires to the extension wires of the~
elongated cord and then applying a precursor of a polyvinyl
formal or phenol-formaldehyde-type thermosetting resin to
the thermistor and bonded wires. The applied precursor is
then cured at elevated temperatures, for example, on the
order of about 350C to 450C, to produce a polyvinyl formal
or phenol-formaldehyde-type resin coating. While this
coatin~ pro~ides adequate electrical insulation and thermal
conductivity, some problems do exist. For example, the
thickness of the overcoating may vary substantially from
one assembly to another, making mass production of such
assemblies very difficult and/cr causing the production of
a substantial amount of off-spec product. The use of
highly elevated curing temperatures may be detrimental to
the thermistor element and result in the production of off-
- spec product. With regard to n vivo applications, the
polyvinyl formal or phenol-formaldehyde-type resins are
very stable in bodily fluids, but can be toxic. Thus, such
.~i.D.9.~31
overcoated thermistor assemblies are often further
overcoated with relatively thick biocompatible material for
use in in vivo applications. Such relatively thick further
overcoatings increase the response time of the thermistor
assemblies.
New sensor assemblies, and in particular thermistor
assemblies, and methods for making such assemblies would
clearly be advantageous.
Hudock U.S. Patent 4,623,5Sg discloses a thermistor
lo which includes a protective coating of an ultraviolet
radiation curable composition containing polyester and
monoacrylate covering the thermistor wafer. An anti-sag or
thixotropic agent may ~e incl~ded in the coating. Portions
of the thermistor leads proximal of the wafer are not
covered by this coating. Also, no other protective
coating, e.g., glass bead, surrounds the wafer. The
polyester-containing coating may tend to be hydrolitically
unstable and/or water absorbing, making such materials of
questionable value in in vivo applications and in other
applications in which the sensor assembly is exposed to
aqueous media.
Dankert U.S~ Patent 3,839,783 discloses bonding the
distal ends of lead wires to a thermistor wafer by coating
the combination with an electrically insulating, thermally
conductive material, such as an aluminum oxide-loaded epoxy
material. Portions of the thermistor leads proximal of the
wafer are not coated, and no other protective coating
surrounds the wafer.
Webler U.S. Patent 4,796,640 discloses a thermistor for
use in measuring the temperature of a fluid flowing within
an individual's body. The bead of a bead-type thermistor
is disclosed as being covered with a thin layer of
electrically insulating material, such as one or more thin
coatings of vinyl and/or urethane to provide saline
production. Portions of the thermistor leads proximal of
~! l Q B~9~3rl
the bead are not disclosed as being covered with this
material. Also, no thixotropic agent is disclosed as a
component of this coating.
Lucey U.S. Patent 4,282,269 discloses coating electronic
components, e.g., capacitors, with ultraviolet radiation
curable protective coating compositions including a borate.
The borate is disclosed as acting to decrease the cure time
whi-le increasing the thickness of the films that are cured.
The preferred materials are ultraviolet light-curable
acrylaté compositions that are substituted with either
epoxy o~ urethane groups and which contain a borate. A
thixotrope can be added, if needed. This patent does not
disclose coating thermistors or thermistor leads, and is
not concerned with the use of sensor assemblies, such as
thermistor assemblies, in n vivo applications.
SummarY of the Invention
New sensor assemblies, for example, thermistor
assemblies, and methods for making the same have been
discovered~. The present assemblies are very effectively
provided with electrically insulating overcoatings of
controlled thickness which can be mass produced. In
addition, particularly with regard to temperature sensor
assemblies, such as thermistor assemblies, the present
assemblies are overcoated with materials which are
effectiveIy thermally conductive, thus permitting such
assemblies to be rapidly or quickly responsive to changes
in the temperature being sensed. The overcoatings on the
present assemblies are preferably biocompatible, making
such assemblies useful for n vivo applications. Further,
such overcoatings are preferably substantially non-water
absorbing and have a high degree of hydrolytic stability.
The present sensor assemblies provide accurate, reliable
and reproducible measurements, and preferably maintain
structural integrity even after being exposed to aqueous
media, for example, bodily fluids, for prolonged periods of
:;
2109~31 ~
time.
The present sensor assemblies can be very effectively
and efficiently produced, for example, on a mass scale,
using the methods of the present invention. Such methods
reduce the number of steps needed to produce sensor
assemblies, as well as produce reliable and reproducible
product at a relatively high rate. Further, the present
methods produce assembled sensors which meet high quality
control standards, for example, in terms of overcoating
thickness and sensor responsiveness (speed of response),
without the production of excessive amounts of out of
specification or off-spec product. In one broad aspect of
the present invention, sensor assemblies are provided which
comprise a sensor including a sensor element adapted to
sense the value of a parameter and to provide an electrical
signal which varies with variations in the parameter value.
Electrically conductive lead wires in- electrical
communication with the sensing element are included. An
elongated member or cord is provided which includes
electrically conductive extension wires each of which is
- bonded to a different one of the lead wires of the sensor
in a bonding zone. An electrically insulating covering,
which may be considered a part of the elongated member, is
located on the extension wires proximal of the bonding
zone. An electrically insulating overcoating is located
over the sensing element, the lead wires and the bonding
zone, and preferably a portion of the electrically
insulating covering, and is derived from a mixture
comprising at least one polymerizable component and at
least one thixotropic component. The thixotropic component
is preferably present in the overcoating precursor mixture
in an amount effective to at least facilitate controlling
the thickness of the overcoating.
A particularly useful embodiment of the present
invention relates to thermistor assemblies. In this
~Q9431 ~
embodiment, the thermistor assembly comprises a thermistor
including a thermistor element, such as the usual
thermistor chip, wafer, bead or the like, a protective
coating substantially surrounding the thermistor element,
preferably hermetically sealed around the thermistor
element, and electrically conductive lead wires in
electrical communication with the thermistor element and
extending beyond the protective coating. An elongated
member is provided and includes electrically conductive
extension wires each of which is bonded to a different one
of the lead wires of the thermistor in a bonding zone, and
an electrically insulating covering located on the
extension wires proximal of the- bonding zone. An
electrically insulating, thermally conductive overcoating
is provided and is located over the protective coating, the
lead wires and the bonding zone, and preferably over a
portion of the electrically insulating covering, and is
derived from a mixture comprising at least one
polymerizable component. and at least one thixotropic
component. The thixotropic component is preferably present
in the overcoating in an amount effective to enhance the
thermal conductivity of the overcoating relatîve to a
substantially identiGal overcoating without the thixotropic
component. This enhanced thermal conductivity reduces the
time required for the thermistor assembly to respond to
variations in the value of the temperature being sensed.
-The present methods for producing sensor assemblies
comprise bonding the electrically conductive lead wires of
a sensor, for example, a thermistor, to the electrically
- 30 conductive extension wires of an elongated member so as to
form composite wires including a bonding zone. A mixture
comprising at least one polymerizable component and at
least one thixotropic component is applied onto the sensor
and the bonding zone, and preferably onto a portion of the
elongated member having an electrically insulating covering
9~31
proximal of the bonding zone. The polymerizable component
or components in the applied mixture are cured. This
applied mixture is preferably exposed to ultraviolet
radiation, gamma ray radiation and/or electron beam
radiation at conditions effective to at least partially
cure the polymerizable component or components in the
applied mixture. The partially cured applied mixture may
be subjected to conditions, for example, elevated
temperatures, for a time sufficient to complete the curing
and/or to more securely adhere the cured applied mixture to
the other components of the assembly. In any event, an
electrically insulating, preferably thermally conductive,
overcoating is formed from the applied mixture. Using a
polymerizable component or mixture of polymerizable
components which forms a polymer in the overcoating in
response to being exposed to one or more forms of radiation
noted above provides substantial advantages. This feature
allows the configuration of the overcoating to be set and
at least partially cured without resort to elevated
temperatures, and excessive transporting and processing of
the partially finished assembly. The use of such forms of
radiation to at least partially cure the polymerizable
component or components very ef~ectively, efficiently and
quickly sets the final configuration, in particular the
thickness, of the overcoating. This method of at least
partially curing the overcoating ~acilitates the mass
production of sensor assemblies with substantiaIly
reproducible sensing, for example, response time,
characteristics. If necessary or desired, after being
exposed to such radiation, the overcoating can be subjected
to elevated temperature for a time sufficient to further
cure or completely cure the polymer/polymerizable component
or components present in the at least partially cured
overcoating and/or to more securely adhere the overcoating
to one or more other components of the thermistor assembly.
, ... . . . .. .. . .. . . . . . . .
~lU9~31
The present overcoatings are effective to provide
electrical insulation, for example, for safe use. Such
overcoatings p~eferably have a dielectric strength of at
least about 500 volts/mil, that is, at least about S00
volts/0.001 inch. The overcoating should be sufficiently
- thick to provide effective electrical insulation. However,
excessively thick overcoatings are to be avoided as
wasteful and, particularly with regard to temperature
sensors, as being detrimental to the operation of the
sensor assembly. In one useful embodiment, the overcoating
preferably has an average- thickness in the range of about
0.0005 inch to about 0.05 inch, more preferably about 0.001
inch to about 0.02 inch.
Preferably, the present overcoatings have at least one
of the following characteristics: is biocompatible, is
hydrolytically stable and is substantially non-water
absorbing. As used herein, the overcoatings are
biocompatible if they can be exposed to bodily (human)
tissue or fluids for a period of time sufficient to achieve
the desired result, for example, a desired medical
diagnosis and/or treatment procedure, with no significant
detrimental effect on the individual whose bodily tissue or
fluids are so exposed. As used herein, the overcoatings
are hydrolytically stable if they remain structurally
intact after being exposed to an aqueous medium, such as
blood or a conventional saline solution, for 72 hours at
37C. As used herein, the overcoatings are substantially
non-water absorbing if they absorb no more than 5%,
preferably no more than 1%, by weight of water after being
exposed to an aqueous medium, such as blood or a
conventional saline solution, for 10 hours at 37C. Such
characteristics of the present overcoating are beneficial,
particularly when the sensor assemblies are to be used in
in vivo medical applications, for example, in conjunction
with a catheter such as a multi-lumen catheter.
~109~31
. 9
The present overcoatings include at least one polymer
derived at least in part from a polymerizable component or
a mixture of polymerizable components. Such polymerizable
component or components are preferably such as to be
capable of being polymerized by expo~ure to ul~raviolet
radiation, ga~ma ray radiation, and/or electron beam
radiation. Any suitable polymer or mixture of polymPrs may
be included in such overcoatings provided that the
- resulting overcoatings function as described herein. In
one embodiment, the polymer is a thermosetting polymer.
Examples of useful polym~rs for inclusion in the present
overcoatings include epoxy polymers, polymers derived from
at least one of methacrylic acid, methacrylic acid esters,
acrylic acid, acrylic acid esters, and mixtures thereof.
Specific examples of polymerizable formulations from which
such polymers can be obtained include the methacrylic acid
ester adhesive formulation sold under the trademark DYMAXR
Multi-care 20159 by Dymax Engineering Adhesives, and the
epoxide/polyol formulation sold under the trademark ENVIBAR
W 1244X3 by Union Carbide Chemicals and Plastics Company
Inc.
~ he mixture from which the overcoating is derived may
include at least one initiator, e.g., at least one
photoinitiator, in an amount effective to initiate the
polymerization of the polymerizable component or
components, particularly if the polymerization is to be
initiated by ultraviolet radiation~ Any suitable initiator
or mixture of initiators, such as those conventionally used
to initiate polymerization in the presence of ultraviolet
radiation, may be included. Care should be exercised to
avoid initiators or amounts of initiators which may have a
detrimental effect on the overcoating or its properties,
for example, its biocompatibility. Examples of useful
initiators include benzophenone, diethyoxyacetophenone,
2,3-dimethyoxy-2-phenylacetophenone, benzoin methyl ether,
,.. ... . . . .. .. .. .. . . .. . . . . . .
~2 1. 0 9 ~ 3 1
'^ . 10
benzoin ethyl ether, benzoin isopropyl ether, benzoin
isobutyl ether, chlorothio-xanthanone, azo-bis-
isobutylronitrile, N-methyl diethanolaminebenzophenone and
the like. Such initiator or initiators are preferably
present in an amount in the range of about 1~ to about 10%,
more preferably about 2% to about 5%, by weight based on
the total weight of the polymerizable component or
components present in the mixture. In addition, catalysts,
such as amines, for example, phenylenediamine;
benzyldimethyl amine; methylbenzyldimethylamine;
dimethylaminomethylphenol, and the like may be used in
amounts effective to promote the initiation mechanism,
generally about 0.05 part to about 1.0 part per 100 parts
of the mixture.
One or more thixotropic components are included in the
present overcoatings and mixtures, for example, to obtain
the result or results noted elsewhere herein. Any suitable
thixotropic component or components may be employed
provided that such component or components function as
described herein. Care should be exercised in choosing the
thixotropic component or components to avoid those
components which may adversely ef~ect the desired
properties, e.g., biocompatability, of the sensor assembly.
The thixotropic component is preferably inorganic. Examples
of useful thixotropic components include silica, such as
fumed silica; colloidial aluminum silicate clays;
carbonates, silicates and sulfates of alkaline earth
metals; metal oxides, such as magnesia; and the like. The
thixotropic component or components are preferably present
in the mixtures and overcoatings in an amount in the range
of about 0.1% to about 15~, more preferably about 0.2% to
about 7%, by weight based on the total weight o~ the
mixtures and overcoatings, respectively.
The present methods for producing sensor assemblies,
3s such as the present sensor assemblies, involve the
39431
11 .
application of a mixture comprising at least one
polymerizable component and at least one thixotropic
component, such as the mixtures described elsewhere herein.
These methods comprise bonding the electrically conductive
lead wires of a sensor, such as described herein, to the
electrically conductive extension wires of an elongated
member so as to form composite wires including a bonding
zone in which the lead wires and extension wires are bonded
together. A mixture, as described above, is applied onto
the sensor and the bonding zone. This applied mixture is
then subjected to conditions effective to cure (polymerize)
the polymerizable component or components therein. The
applied mixture is preferably exposed to ultraviolet
radiation, gamma ray radiation and/or electron beam
radiation at conditions effective to at least partially
cure the at least one polymerizable component in the
applied mixture. Elevated temperatures, for example, in the
range of about 100C to about 150C, may be employed to
further cure the overcoating and/or to enhance the adhesion
of the overcoating to one or more other components of the
assembly. An electrically insulating, preferably thermally
conductive, overcoating is formed from the applied
mixture.
The bonding step preferably includes spot welding the
lead wires to the extension wires.
The applying step preferably includes dipping the sensor
and the bonding zone into a quantity of the mixture. In one
embodiment the elongated member includes an electrically
insulating covering located on the extension wires proximal
of the bonding zone. The applying step acts to apply the
mixture onto a portion of this covering. In this manner,
the entire sensor assembly is electrically insulating.
The invention, together with additional features and
advantages thereof, may best be understood by reference to
the following description taken in connection with the
21D9~3 1
12
accompanying illustrative drawings.
Brief Descri~tion of the Drawinas
Fig. 1 is a schematic view partly in cross section
showing 3n embodiment of the present thermistor assembly.
Fig. 2 is a partial cross sectional view taken generally
along line 2-2 of Fig. 1.
Fig. 3 is a cross-sectional view taken generally along
line 3-3 of Fig. 1. ~-
Fig. 4 is a block flow diagram illustrating one
embodiment of the present method of producing sensor
assemblies.
Fig. 5 is a side view of a multi-lumen medical catheter
employing a thermistor assembly in accordance with the
present invention. -~
Fig. 6 is a view, partially in cross-section, taken
génerally along line 6-6 of Fig. 5.
Detailed Descri~tion of the Drawings
Fig. 1 illustrates a thermistor assembly, shown
generally at 10, in electrical communication with a
ronventional temperature monitor unit 12. Thermistor
assembly 10 includes a thermistor, shown generally at 14,
an elongated extension cord, shown generally at 16, and an
overcoating 18.
Thermistor 14 includes a thermistor chip 20, of
conventional design, a hermetically sealed glass bead 22
which forms a protective coating around chip 20, and two
lead wires 24 and 26 which are electrically connected to
chip 20 and extend beyond glass bead 22. Lead wires 24 and -~
26 act to transmit electrical signals to and from chip 20, ~;
and may be made of any suitable electrically conductive,
preferably metallic, material. In a particularly use~ul
embodiment, lead wires 24 and 26 are made of a platinum-
containing alloy. Thermistor 14 is often provided as a
basic unit from which thermistor assembly lO is produced or
manufactured.
210~31
_ 13
Elongated extension cord 16 includes extension wires 28
and 30, and an electrically insulating covering 32.
Extension wires 28 and 30 extend distally beyond the distal
end 34 of cord 16. However, these extension wires 28 and
are ultimately in electrical communication with
temperature monitor unit 12, so that together with lead
wires 24 and 26 they provide for electrical communication
between chip 20 and unit 12. Extension wires 28 and 30 may
be made of any suitable electrically conductive,
preferably, metallic, material. The materials from which
lead wires 24 and 26, and extension wires 28 and 30 are
- made should be chosen from materials which can be
effectively~bonded together, for example, so as to maintain
the structural integrity of the bond during use of the
assembly 10 and to maintain the integrity of the electrical
signals to be transmitted through such wires. In one
embodiment, the;extension wires 28 and 30 are made of a
- nickel alloy, such as a nickel magnet wiring material.
Each of the lead wires 24 and 26 is bonded to extension-~ 20 wires 28 and 30, respectively, for example, by conventional
spot welding techniques. $his bonding occurs in a bonding
zone 36 which includes the~proximal end portions of lead
wires 24 and 26 and the distal end portions of extension
wires 28 and 30. ~n any event, wires 24 and 28 and wires
~ 26 and 30 are effectively bonded together so that such
wires are in electrical communication with each other.
Overcoating 18 inc~ludes an epoxy polymer, such as that
derived from the epoxide/polyol formulation sold under the
trademark ENVIBAR W 1244X3 by Union Carbide Chemicals and
; 30 Plastics Company, Inc. Overcoating 18 also includes solid
particles 38 of a thixotropic component, such as fumed
silica, for example, that sold under the trademark Cab-O-
Sil by Cabot Corp. Particles 38 act to enhance the thermal
conductivity o~ overcoating 18 and, during the assembly
operation, ~acilitate controlling the thickness o~ the
.
.. .. . . ..
~109~31
1 4
overcoating. Overcoating 18 is preferably substantially
free of borate components, in particular effective amounts
of one or more borate components.
Overcoating 18 has an average thickness, particularly
around the distal half of the glass bead 22, in the range
of about 0.005 inch to about 0.02 inch. Overcoating 18
extends around glass bead 22, lead wires 24 and 26, bonding
zone 36, the exposed distal portions of extension wires 28
and 30 and the distal end portion 39 of covering 32. The
dielectric strength of overcoating 18 is at least about 500
volts/mil, for example, about 1800 volts/mil, and, together
with covering 32, provides assembly 10 with effective
electrical insulation.
In addition, overcoating 18 is biocompatible, has
substantial hydrolytic stability and is substantially non-
water absor~ing. This combination of features makes
- thermistor assembly 10 very effective for use in in vivo
medical applications. -
Figs. 5 and 6 illustrate one very useful application for
the thermistor assembly 10. A multi-lumen catheter, shown
generally at 40, includes an elongated, flexible catheter
body or tube 42, for example, sized to be received within
a vein or artery and moved into the heart of a human
medical patient. The catheter 40 has a proximal end 44 and
a distal end 46, and includes a balloon 48 adjacent the
dista~ end. It should be noted that thermistor assembly 10
can be used in other applications, including other catheter
applications.
The catheter 40 has a plurality of lumens, including a
central lumen 50 and a thermistor lumen 52, as well as
other lumens, such as a balloon inflation lumen, a through
lumen, an injectate lumen and an electrical wires lumen.
All of the lumens extend longitudinally within the tube 42
from the proximal end 44 to the distal end 46. However,
the balloon inflation lumen is plugged by a plug at the
, ' ' ~
.~.
- 21109~31 ,-
:
distal end 46. The thermistor lumen 52, the injectate
lumen and the electrical wires lumen are similarly plugged
at the distal end 46. In addition, the central lumen 50
carries an illuminating optical fiber 54 and an imaging
optical fiber 56 and is fully closed or plugged by these
fibers and an adhesive which retains these fibers in the
central lumen 50. The optical fibers 54 and 56 extend
comp}etely through the central lumen 50 from the proximal
end 44 to the distal end 46. Only the through lumen is
lo capable of conducting a fluid completely through the
catheter 40 from the proximal end 44 to the distal end 46.
The through lumen terminates in a distal port at the distal
end 46 of the catheter. For additional details on
catheters of this type and methods for manufacturing such
catheters, see commonly assigned U.S. Patent Application
Serial No. , filed (Attorney's Docket
No. D-2344), which is hereby incorporated in its entirety
herein by reference. .
The thermistor assembly 10 is mounted within the
thermistor lumen 52 by a thermistor mounting body 58 as
shown in Fig. 6. The mounting body 58 has a somewhat
concave outer surface 60 which cooperates with the tube 42
to define a cavity 62 which opens radially outwardly at the
opening 64 of the tube 42. Mounting body 58 is adhesively
held in place in thermistor lumen 52.
:: The thermistor assembly 10 is partially embedded in the
mounting body 58 and projects from the mounting body into
the cavity 62. The thermistor assembly 10 projects into
the cavity 62 so that fluid can enter and flow through the
cavity, and the thermistor assembly 10 is in good heat-
transfer relationshîp to the fluid passing over the
catheter 40 at that location. A portion of the volume of
the cavity 62 is occupied by the thermistor assembly 10.
The opening 64 and the cavity 62 are sufficiently large so
3S that fluid flowing along the tube 42 can readily flow over
- `~109~3 l
the portion of the thermistor assembly 10 which projects
into the cavity 62. This places the thermistor assembly 10
in good heat-transfer relationship to any fluid flowing
along the tube 42 at that location.
S The thermistor assembly 10 is elongated and is oriented
so that its longitudinal dimension extends generally
longitudinally of the thermistor lumen 52. ~hus, the long
axis of the thermistor assembly 10 extends generally
parallel to the direction of any fluid flowing along the
longitudinal axis of the catheter 40.
The mounting body 58 can be constructed in different
ways, but preferably, it includes a base 66 of electrical
insulating material located between a wall 68 which
separates the lumens 50 and 52 and the thermistor assembly
lS 10 and a thermally conductive ~ayer 70. The thermally
conductive layer 70 comprises a matrix of electrically
insulating material and a filler carried by the matrix.
Both the base 66 and the matrix are preferably constructed
of a material which is adherent to the tube 42 and which is
an electrical insulator. The material of the base 66 is
also preferably a good thermal insulator to insulate the
thermistor assembly 10 from any fluid flowing in the
through lumen of th~ catheter 40. Generally, polymeric
materials can be used for the base and the matrix with
urethane and epoxy being preferred.
The filler is constructed of a material which is more
thermally conductive than the electrical insulating
material. For example, the filler may be ceramic, carbon,
graphite, or a metal, such as silver, nickel, gold,
platinum and aluminum. Examples of suitable ceramics are
aluminum oxide, aluminum nitride, boron oxide, boron
nitride, silicon oxide and silicon nitride. For example,
the filler may be in the form of strands, chopped fibers or
particles, with dentritic-shaped particles being preferred
for improved thermal conductivity.
21D9~31 :
17
By way of example, a preferred ceramic-filled epoxy is
EP21TDCLV-2AN obtainable from Master Bond Inc. Ceramic is
the preferred material for the filler because it is not
electrically conductive.
5The base 66 may be of various dif~erent configurations
and, in this embodiment, has a concave outer surface 72
facing outwardly toward the opening 64. Preferably, the
outer surface 72 is spaced from the thermistor assembly lO
. to provide space between the base 66 and the thermistor
10assembly 10 for the thormally conductive layer 70. The
thermally conduotive layer 70 preferably is sandwiched
between the thermistor assembly 10 and the base 66 and
extends~part way around the sides of the thermistor
assembly 10. Thus, the thermally conductive layer is
15located to facilitate heat transfer`from the fluid outside
the tube 44 to the thermistor assembly 10. The thermally
conductive layer 70 has sufficient electrical insulating or
dielectric properties so as to be safely usable.
If desired, a very thin layer 74 of the base material,
20such as urethane or epoxy, may be placed over the exposed
regions of the thermistor assembly lO. The layer 74 is
- really not part of the mounting body in the sense that it
: serves any mounting function although it is adhered to the
thermistor assembly 10 and the thermally conductive layer
2583. The layer 74 is very thin because it is only used for
electrical isolation, and it may or may not be considered
part of the mounting body 63.
If desired, the thermally conductive layer 70 can be
omitted, and the entire mounting body can be comprised of
30the base 66. In .this event, the ;conductive layer 70 is
replaced with the base 66 so that the mounting body 58 has
the same configuration as the combined base 66 and
conductive layer 70 shown in Fig. 6.
- In use of the catheter 40, the catheter tube 42 is
: 35introduced through a vein or artery of a patient and into
.
. 2109~31
18
the heart using known techniques. The balloon 48 is
inflated through the balloon inflation lumen, and the
inflated balloon is used to carry the distal end 46 of the
catheter to the desired location. For example, the balloon
19 is carried into the pulmonary artery. The location of
the tube 42 within the heart will depend upon the procedure
to be carried out.
For example, to calculate ejection fraction, the tube 42
is inserted into the heart so as to place the injectate
port in the right atrium, the thermistor assembly 10 into
the pulmonary artery and the distal end 46 into the
pulmonary artery. A bolus of cold fluid is then injected
into the right atrium through the injectate port and
allowed to mix with the bloodstream in the right ventricle.
The blood and cold fluid mixture flow along the catheter
tube and over the thermistor assembly 10 in the pulmonary
artery. The temperature of the mixture changes with each
heartbeat, and the thermistor assembly 10 can track eaoh
temperature change so as to provide a stepped temperature
chart. This information can then be processed in
accordance with known techniques to provide ejection
fraction. Pressure can be monitored, if desired, through
the through lumen of catheter 40.
Referring now to Fig. 4, the manufacture of thermistor
assembly 10 is illustrated. It should be understood that
other sensor assemblies can be produced using substantially
similar or analogous manufacturing methods. Thus, such
sensor assemblies and methods for making such other sensor
assemblies are within the scope of the present invention.
The thermistor 14 is positioned to be parallel to the
edge of the elongated extension cord 16, which is
conveniently wound onto a spool. During the bonding step,
generally shown at 80, the lead wires 24 and 26 are bonded
to the extension wires 28 and 30, respectively. This
bonding can be done in any suitable manner, provided that
~109~31 ::
19 :`
firm (strong) wire-to-wire attachment is o~tained, and the
resulting composite wire is effectively electrically
conductive. The area of the wires at which the wires are
actually bonded together is referred to as the bonding zone
36. The wires can be very effectively bonded together
using conventional spot welding techniques.
After the bonding, the thermistor 14 and bonding zone 36
is dipped in acetone or other suitable liquid medium for a
period of time, on the order of about 2 seconds to about 1
minute, for example, about 5 seconds, sufficient to clean
and/or rinse contamination from these components. As much
o~ the exposed extension wires 28 and 30 as possible are
preferably subjected to this dipping step.
The bonded thermistor 14, bonding zone 36 and exposed
extension wires 28 and 30 are then dipped în acetic acid,
or other suitable etching medium, for a period of time, on
the order of about 10 seconds to about 10 minutes, for
example, about 2 minutes, sufficient to etch or otherwise
condition the lead wires, bonding zone and extension wires
ZO so that such conditioned wires and zone are more strongly
adhered to the overcoating 18 to be placed thereon relative
to the unconditioned wires and zone. After this
conditioning, the thermistor bonding zone and extension
wires are dipped in a liquid medium, e.g., acetone, for
about 2 seconds to about 1 minute, for example, about 10
seconds, to rinse off the conditioning medium~
The conditioned the~mistor, bonding zone, extension
wires and distal end portion of the covering of the
extension cord are then dipped into a quantity of a mixture
comprising polymèrizable components and about 5% by weight
of fumed silica particles. This mixture is curable by
exposure to ultraviolet radiation. A particularly useful
formulation of polymerizable component for use in the
present invention is the epoxide/polyol-containing mixture
sold under the trademark ENVIBAR W 1244X3, described
2iO9431 `
-- 20
previously. This applying step, shown generally at 82 in
Fig. 4 can be performed using techniques other than
dipping. For example, the mixture may be sprayed on,
painted on and the like. In any event, the applying step
produces a coating of a curable monomer mixture including
a thixotropic agent on the thermistor 14, bonding zone 36,
exposed extension wires 28 and 30 and the distal end
portion 39 of covering 32. In the dipping embodiment, the
thickness of the mixture coating depends at least partially
on the rate at which the bonded thermistor is removed from
the coating mixture. For example, with a thermistor having
a glass protective coating with a diameter of about 0.015
inch to about 0.017 inch, a coated diameter of about 0.020
inch to about 0.024 inch is obtained by withdrawing the
bonded thermistor from the coating mixture at the rate of
about 3 to about 5 inches/minute.
After this applying step 80, the coated thermistor is
examined, for example, under a microscope, for coating
defects. If any such defects exist, the applying step is
repeated.
After the coated thermistor passes the defect
examination, it is exposed in a exposing step, shown
generally at 84 in Fig. 4, to ultraviolet radiation, for
example, from a ultraviolet lamp, at conditions effective
to partially cure the polymerizable components in the
applied mixture. This exposing step 84 occurs for a period
of time, for example, in the range of about 10 seconds to
about 10 minutes or more. In one embodiment, the coated
thermistor is exposed to ultraviolet radiation for about 1
minute, then rotated 180 and exposed to ultraviolet
radiation for another minute.
The partially cured coated thermistor together with the
entire spool of extension cord is then subjected to
elevated temperatures in a temperature treatment step,
shown generally at 86 in Fig. 4, for a period of time to
D19 4:'31 ~
completely cure the coating. For example, the partially
cured coated thermistor/spool combination can be placed in
a conventional circulation oven and left undisturbed at
about 100 C to about 150C, e.g.,~ about 120 C, for about
5 minutes to about 3 hours, e.g., about 30 minutes. -
The completely cured thermistor assembly which has a
configuration as shown in Fig. 1, is cooled to room
temperature prior to being incorporated into a temperature
sensing system, such as the catheter system noted
previously.
While this invention has been described with respect to
various specific examples and embodiments, it is to be
understood that the invention is not limited thereto and
that it can be variously practiced within the scope of the
following claims.
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