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Claims  |
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We claim:
1. An electrochemical measuring electrode device for transcutaneous
measurement of a blood parameter, said device comprising:
a body formed of a heat conductive material, said body including a surface
part for application to a skin surface in heat conductive relationship
therewith, sensor means for operatively responding to said blood
parameter, and first thermostating means for thermostating said body to a
predetermined temperature,
said device further comprising, a container-shaped jacket formed of a heat
conductive material, said jacket including an annular surface part
defining an opening in said jacket, said body being mounted within said
jacket in spaced heat-insulating relationship therewith, said surface part
of said body being substantially flush with said annular surface part so
that said annular surface part is in heat conductive relationship with the
skin surface when said surface part of said body is in heat conductive
relationship with the skin surface, said jacket further including second
thermostating means for thermostating said jacket to such a temperature
that the heat transport or heat flux from said body is substantially
unidirectional, whereby the spaced heat-insulating relationship between
said body and said jacket enables said jacket to establish, in operation,
a virtual heating jacket in the skin beneath said annular surface part so
as to substantially direct all heat flow from said body to skin layers
directly beneath said body.
2. The electrochemical measuring electrode device according to claim 1,
wherein said body has an outer periphery, said jacket has an inner surface
adjacent to the outer periphery of said body, and the spaced
heat-insulating relationship between said body and said jacket is such
that a substantially narrow space is defined between the outer periphery
of said body and the adjacent inner surface of said jacket.
3. The electrochemical measuring electrode device according to claim 1,
wherein said first and second thermostating means comprise means for
heating said body and said jacket to the same temperature so as to obtain
a zero heat flux between said body and said jacket.
4. The electrochemical measuring electrode device according to claim 1,
wherein said body has a substantially circular cylindrical shape.
5. The electrochemical measuring electrode device according to claim 4,
wherein said jacket includes a substantially annular part which is
arranged coaxially relative to said body.
6. The electrochemical measuring electrode device according to claim 1,
wherein said body is disc-shaped.
7. The electrochemical measuring electrode device according to claim 1,
wherein said first thermostating means comprises an NTC-resistor and a
heating resistor.
8. The electrochemical measuring electrode device according to claim 1 and
further including a first thick film substrate, said first thermostating
means being arranged on said first thick film substrate.
9. The electrochemical measuring electrode device according to claim 8,
wherein said first thermostating means comprises thick film components
disposed on said first thick film substrate.
10. The electrochemical measuring electrode device according to claim 8,
wherein said body is formed of said first thick film substrate.
11. The electrochemical measuring electrode device according to claim 8,
wherein said first thick film substrate has a plane or plane-convex shape.
12. The electrochemical measuring electrode device according to claim 8,
wherein said first thick film substrate has a thickness of about 0.2-1.5
mm, and preferably about 0.3-0.8 mm.
13. The electrochemical measuring electrode device according to claim 8,
wherein said first thick film substrate has a diameter of about 5-12 mm.
14. The electrochemical measuring electrode device according to claim 8,
wherein said first thick film substrate is made of alumina or beryllia.
15. The electrochemical measuring electrode device according to claim 1,
wherein said second thermostating means comprises an NTC-resistor and a
heating resistor.
16. The electrochemical measuring electrode device according to claim 8,
wherein said jacket further includes a second thick film substrate and
said second thermostating means is arranged on said second thick film
substrate in heat-conductive connection with said jacket.
17. The electrochemical measuring electrode device according to claim 16,
wherein said second thermostating means comprises thick film components
disposed on said second thick film substrate.
18. The electrochemical measuring electrode device according to claim 16,
wherein said second thick film substrate comprises a circular substrate.
19. The electrochemical measuring electrode device according to claim 16,
wherein said second thick film substrate has a plane or plane-convex
shape.
20. The electrochemical measuring electrode device according to claim 16,
wherein said second thick film substrate is made of alumina or beryllia.
21. The electrochemical measuring electrode device according to claim 1,
wherein the thermal resistance between said jacket and said body is at
least one order of magnitude (power of 10) greater than the thermal
resistance between the body and the capillary bed beneath the skin
surface.
22. The electrochemical measuring electrode device according to claim 1,
wherein said sensor means comprises measuring means for measuring the
partial pressure of a blood gas.
23. The electrochemical measuring electrode device according to claim 22,
wherein said measuring means comprises a cathode of a noble metal capable
of electrochemical reduction of oxygen, and an anode cooperating with said
cathode and preferably being a silver anode, for measuring the partial
pressure of oxygen in blood.
24. The electrochemical measuring electrode device according to claim 1,
further comprising a membrane and an electrolyte solution, said membrane
being adjacent to said surface part of said body so as to define a space
wherein said electrolyte solution is confined.
25. A method of transcutaneous measurement of a blood parameter,
comprising:
applying, to a skin surface of a person, an electrochemical measuring
device comprising, in combination:
a body formed of a heat conductive material, said body including a surface
part for application to the skin surface in heat-conductive relationship
therewith, sensor means for operatively responding to said blood
parameter, and first thermostating means for thermostating said body to a
predetermined temperature, and a container-shaped jacket formed of a
heat-conductive material, said jacket including an annular surface part
defining an opening in said jacket, said body being mounted within said
jacket in spaced heat-insulating relationship therewith, said surface part
of said body being substantially flush with said annular surface part so
that said annular surface part is in heat conductive relationship with the
skin surface when said surface part of said body is in heat conductive
relationship with the skin surface, and said jacket further including
second thermostating means for thermostating said jacket to a particular
temperature,
thermostating said body to a predetermined temperature with said first
thermostating means,
thermostating said jacket to such a temperature with said second
thermostating means that the heat transport or heat flux from said body is
substantially unidirectional so that said jacket establishes a virtual
heating jacket in the skin surrounding the periphery of said body to
substantially direct all heat from said body to skin layers directly
beneath said body,
measuring the power supplied for thermostating said body to said
predetermined temperature to enable estimation of the blood flow in the
skin with which the body is in heat conductive relationship, and
measuring the blood parameter by means of said sensor means.
26. The method according to claim 25, wherein said body and said jacket are
thermostated to the same temperature.
27. The method according to claim 25, wherein said blood parameter is the
partial pressure of a blood gas.
28. The method according to claim 25, wherein, in an alternative
operational mode, said first thermostating means includes temperature
sensing means for measuring the temperature of said first thermostating
means, said second thermostating means includes temperature sensing means
for measuring the temperature of said second thermostating means, and said
jacket is thermostated to such a temperature that the temperature
registered by the temperature sensing means of said first thermostating
means and the temperature registered by the temperature sensing means of
said second thermostating means are identical to one another and,
consequently, identical to the deep body temperature. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to electrochemical measuring electrode
devices for transcutaneous measurement of a blood parameter, such as the
partial pressure of a blood gas. The transcutaneous measuring technique is
well-known in the art. In accordance with the transcutaneous measuring
technique, an electrode device for measuring the blood parameter in
question is applied to a skin surface of a person in whom the blood
parameter is to be measured. The electrode device is thermostated to a
predetermined temperature, normally (when the blood parameter to be
measured is, e.g., the partial pressure of a blood gas such as oxygen) a
temperature above normal skin temperature so as to cause local hyperaemia
in the skin surface in contact with the electrode.
Above certain minimum levels of perfusion in the skin area where the
transcutaneous measurement is performed, parameters measured
transcutaneously, e.g. blood gas partial pressures, reflect the
corresponding arterial values which are the values normally used for
clinical purposes. Below such minimum levels, the parameters measured
transcutaneously can no longer be considered as reflecting the arterial
values.
For this reason, it is important to monitor the local capillary blood flow
concomittantly with the local transcutaneous measurement of a blood
parameter. Furthermore, calculation methods have been suggested which
convert the transcutaneously measured values into calculated values
correlating to a higher degree with actual arterial values when, in
addition to the perfusion, the metabolic oxygen consumption, the capillary
temperature, and the skin diffusion gradient are also known or estimated.
It has been suggested, cf. e.g. Journal of Clinical Engineering, 6, No. 1,
January/March 1981, pp 41-47 (Reference 1), Birth Defects, Original
Article Series Vol. XV, No. 4, pp 167-182, 1979 (Reference 2), and
Critical Care Medicine, October 1981, Vol. 9, No. 10, pp 736-741
(reference 3) to monitor the local capillary blood flow by measuring the
power supplied to the transcutaneous electrochemical measuring devices to
keep the devices at a constant temperature.
However, according to Reference 1, merely about 10-15% of the total sensor
power is perfusion-dependent. Reference 2 suggests a device where the heat
exchange with the surroundings is limited by means of a heat shell over
the electrode device, the heat shell being circulated with water at
electrode temperature, but reports that only about 30% of the heat
transferred from the electrode to the skin is flow related. Reference 3
suggests a combined O.sub.2 /CO.sub.2 and flow sensor which is adapted to
be mounted on the forearm of a test person. Apart from a first
servo-controlled heater/thermistor arranged in heat-conductive contact
with a first heater assembly and serving the above described purpose of
causing local hyperemia in the skin surface in contact with the sensor, a
second servo-controlled heater/thermistor is included and arranged in
heat-conductive contact with a second heater assembly arranged on the
outside of the sensor. The second servo-controlled heater/thermistor is
adapted to maintain the temperature of the second heater assembly at a
temperature of 0.5.degree. C. below the temperature of the first heater
assembly. Thus, the second heater assembly which is not contacted with the
skin surface merely serves thermal insulation purposes. When employed in
conjunction with an occlusive system which is adapted to be arranged
enclosing the entire forearm of a test person or patient and, furthermore,
increases the insulation properties, the sensor is reported to be able to
register a perfusion-dependent heat transfer to the skin of approximately
50% of the total sensor power.
SUMMARY OF THE INVENTION
The invention provides an electrochemical measuring electrode device for
transcutaneous measurement of a blood parameter, said device comprising,
in combination:
a body of a heat-conductive material having a surface part adapted to be
applied to a skin surface in heat-conductive relationship therewith, said
body including sensor means adapted to respond, in operation, to said
blood parameter, and first thermostating means for thermostating said body
to a predetermined temperature,
and a container-shaped jacket having an annular surface part defining an
opening in said jacket, said body being mounted within said jacket in
spaced heat-insulating relationship therewith, said surface part of said
body substantially flushing with said annular surface part so that said
annular surface part is in heat conductive relationship with said skin
surface when said surface part of said body is in heat conductive
relationship with the said skin surface, said jacket including second
thermostating means for thermostating said jacket to such a temperature
that the heat transport or heat flux from said body is substantially
unidirectional, and the spaced heat-insulating relationship between said
body and said jacket being such that said jacket establishes, in
operation, a virtual heating jacket in the skin beneath said annular
surface part so as to substantially direct all heat flow from said body to
skin layers directly beneath said body.
Normally, the spaced heat-insulating relationship between said body and
said jacket will be such that a substantially narrow space is defined
between the outer periphery of said body and the adjacent inner surface of
said jacket.
The jacket may, in principle, be heated to a temperature which is different
from the temperature of the body, but it is generally preferred that the
body and the jacket are adapted to be heated to the same temperature so as
to obtain a zero heat flux between said two bodies.
Like in conventional electrode devices, the construction will normally be
most suitable when the body has a substantially circular cylindrical
shape, and the jacket will then suitably have a substantially annular wall
part which is arranged coaxially relative to said body.
In order to obtain a high degree of sensitivity to and a fast response on
perfusion changes, the thermostating time constant and the thermal time
constant of the body should both be low. The thermostating time constant
(related to the active, heating function of the body) should be as low as
possible to permit the system to respond immediately to power transport
from the body and maintain a constant temperature. The thermostating time
constant is proportional to the heating resistance of the system
constituted by the body and the heating means heating the body, and hence,
the effective heat-conductive contact between the body and the heating
means of the first thermostating means should be as high as possible. The
thermal time constant (related to the passive, cooling function) should be
low to permit the system to immediately sense a higher power consumption
by the blood flow. The thermal time constant will be proportional to the
thermal capacity of the body, which means that in order to obtain a low
thermal capacity, the volume of the body should be as small as possible.
At the same time, the heat-conductive contact area between the body and
the skin surface should be as large as possible. All of these
considerations are best fulfilled when the body is disc-shaped, allowing
for an optimum heat-conductive contact between the heating means of the
first thermostating means and for the smallest possible volume at a given
heat-conductive skin contact area.
The first thermostating means may, in principle, comprise any combination
of heating means and temperature sensing means which will be suitable for
the purpose in view of the above considerations. One combination which has
been found suitable in practice comprises an NTC-resistor and a heating
resistor.
A compact and flat construction is obtainable when said first thermostating
means is arranged on a first thick film substrate, and according to a
preferred embodiment of the invention, the first thermostating means is
constructed as thick film components on said first thick film substrate,
the said thick film substrate preferably constituting said body.
In accordance with what has been stated above, this thick film substrate
preferably has a plane or plane-convex shape. The thick film substrate
will preferably have a thickness of about 0.2-1.5 mm, in particular about
0.3-0.8 mm. The diameter of the thick film substrate will normally be
about 5-12 mm.
Thick film substrates which are especially suitable for the purpose of the
invention because of their favourable combination of electrically
insulating properties and specific heat capacity properties are thick film
substrates made of alumina or beryllia.
The body may also be made using thin film technology. In such case, the
sensor means and the thermostating means will normally be applied on the
body by means of thin film technique. The thin film substrate may, e.g. be
made of ceramic material such as alumina or beryllia, or of silicon. When
using thin film technique for the body (and optionally for other
components of the electrode device, in particular also for the jacket
thermostating means), the dimensions of the body may be the same as stated
above for thick film bodies, but the thin film technique also permits the
use of thinner and/or smaller bodies, optionally with several sensors
applied on one and the same body.
The thermostating time constant of the jacket should be as low as possible
in order to permit the jacket to respond as fast as possible in
thermostating. On the other hand, the thermal time constant of the jacket
relating to passive cooling of the jacket should be as high as possible.
Thus, the jacket may be made from any material showing suitable specific
heat capacity for the purpose, e.g. a metal such as copper or silver. The
thermostating means thermostating the jacket may suitably comprise similar
components as the thermostating means thermostating the body. Thus, this
second thermostating means suitably comprises an NTC-resistor and a
heating resistor and is suitably arranged on a thick film substrate in
heat-conductive connection with the jacket. Likewise, this second
thermostating means is suitably constructed as thick film components on
said thick film substrate, which suitably is a circular substrate that
preferably has a plane or plane-convex shape. Also this substrate is
preferably made of alumina or beryllia.
The thermal resistance between the body and the jacket should be
sufficiently high to substantially eliminate thermal crosstalk between the
body and the jacket. For this reason, the thermal resistance between said
jacket and said body should preferably be at least one order of magnitude
(power of 10) greater than the thermal resistance between the body and the
capillary bed beneath the skin surface. At a circular body of alumina
having a diameter of about 10.5 mm, this condition is fulfilled when the
distance between the outer periphery of the body and the adjacent inner
surface of the jacket is 2 mm and the distance between the upper surface
of the body and the lower surface of the jacket is 3 mm.
The sensor means of the electrochemical measuring electrode device may be
sensor means adapted for measurement of any blood parameter which can be
measured by means of an electrochemical measuring electrode, e.g., pH or
the partial pressure of a blood gas. The sensor means may be of any
suitable type adapted to be included in the selected type of body.
Examples of sensor means suitable for the present purpose appear, e.g.,
from Danish Patent Application No. 1650/81 and 1676/81, both in the name
of Radiometer A/S and may, e.g., comprise sensor means for measuring the
partial pressure of oxygen and/or carbon dioxide. When the sensor means
are adapted for the measurement of the partial pressure of oxygen, they
may suitably comprise a cathode of a noble metal capable of
electrochemical reduction of oxygen, and an anode cooperating with said
cathode and preferably being a silver anode.
In accordance with well-known principles for the construction of
electrochemical measuring electrode devices, the device according to the
invention will normally comprise a membrane and an electrolyte solution,
said membrane being arranged adjacent to said surface part of said body so
as to define a space wherein said electrolyte solution is confined.
The invention also relates to a method for transcutaneous measurement of a
blood parameter, said method comprising: applying, to a skin surface of a
person, an electrochemical measuring device comprising, in combination:
a body of a heat conductive material having a surface part adapted to be
applied to the skin surface in heat-conductive relationship therewith,
said body including sensor means adapted to respond, in operation, to said
blood parameter, and first thermostating means,
and a container-shaped jacket having an annular surface part defining an
opening in said jacket, said body being mounted within said jacket in
spaced heat-insulating relationship therewith, said surface part of said
body substantially flushing with said annular surface part so that said
annular surface part is in heat conductive relationship with said skin
surface said jacket including second thermostating means, the spaced
heat-insulating relationship between said body and said jacket being such
that said jacket is capable of establishing a virtual heating jacket in
the skin beneath said annular surface part so as to substantially direct
all heat flow from said body to skin layers directly beneath said body.
thermostating said body to a predetermined temperature,
thermostating said jacket to such a temperature that the heat transport or
heat flux from said body is substantially unidirectional, and so that said
jacket establishes a virtual heating jacket in the skin surrounding the
periphery of said body so as to substantially direct all heat from said
body to skin layers directly beneath said body,
measuring the power supplied for thermostating said body to said
predetermined temperature so as to estimate the blood flow in the skin
with which the body is in heat conductive relationship,
and measuring the blood parameter by means of said sensor means.
The measurement of the blood parameter in question is performed in the
normal manner, suitable utilizing normal amplifying and/or recording
means.
The body and the jacket are preferably thermostated to the same temperature
to obtain a zero heat flux therebetween.
Conventionally, when measuring blood flow, the power eliminated by
perfusion below the electrode may be expressed in the following manner:
Q=F.times.C.times..DELTA.T.times.A
wherein Q is the power being eliminated, F is the blood flow, C is the heat
capacity of the blood, .DELTA.T is the temperature increase of the blood,
i.e. the difference between the capillary temperature, T.sub.C, and the
arterial temperature or the deep body temperature, T.sub.DBT, and A is the
area of the electrode device. This equation may be rearranged in the
following manner:
F=Q/(C.times..DELTA.T.times.A)
Q may be measured by measuring the power, P.sub.F, before occlusion and by
measuring the power, P.sub.U, during occlusion, since
Q=P.sub.F -P.sub.U.
A and C are constants, while .DELTA.T may be measured. As mentioned above
.DELTA.T=T.sub.C -T.sub.DBT
wherein T.sub.DBT may be estimated to approximately 34.degree.-35.degree.
C. for an application site on the forearm or measured in a manner to be
described below. T.sub.C may be calculated from the electrode temperature,
T.sub.E, from P.sub.F, and the thermal resistance, R, from the electrode
to the capillary tissue, since
T.sub.E -T.sub.C =P.sub.F .times.R
which may be rearranged into
T.sub.C =T.sub.E -P.sub.F .times.R.
P.sub.U, i.e. the power generated during occlusion, may be determined
during a single occlusion whereafter F may be registered continuously.
In case the deep body temperature is estimated, the above described method
for measuring the blood flow, F, does, however, suffer from one major
drawback since the measuring result may be affected by a change in deep
body temperature, T.sub.DBT. Such a change in deep body temperature may
cause a major change of the power, Q, being eliminated and, consequently,
a major change of the actual measuring result of the blood flow.
In an article by Fox and Sullivan in Journal of Physiology 1970, 212, pp
8-10, a method for measuring the deep body temperature, T.sub.DBT, at skin
surface is described. In an article by Kobayashi, Nemoto, Kaniya and
Togawa in Medical and Biological Engineering, May 1976, pp. 361-363 a
refinement of the above method for measuring the deep body temperature is
described. A probe for carrying out the measuring method is also described
and comprises two thermistors arranged on top of one another within a
jacket-shaped encasing of heat-conductive material which is provided with
heating means. The upper thermistor is arranged in heat-conductive contact
with the jacket-shaped encasing which is adapted to be arranged in contact
with the skin surface of a test person or a patient so that the lower
thermistor arranged within the encasing is also arranged in contact with
the skin surface. It is described that the deep body temperature,
T.sub.DBT, may be measured by controlling the heating of the encasing in
such a manner that the temperature difference between the two thermistors
becomes zero, i.e. so that the heat flow across the probe is zero. When
the heat difference between the two thermistors is zero the temperature
determined by any of said two thermistors equilibrates the deep body
temperature, T.sub.DBT.
In accordance with a particular feature of the present invention, the above
mentioned deep body temperature measuring method may also be carried out
by means of the electrochemical measuring electrode device according to
the invention. By virtue of the special jacket configuration contacting
the skin surface, the electrochemical measuring electrode device according
to the invention is, in an alternative operational mode, adapted to carry
out the said measuring method and, thus, in a very elegant way provide
deep body temperature measuring results for the above described blood flow
measuring method.
In this alternative operational mode, the jacket is thermostated to such a
temperature that the temperature registered by the temperature sensing
means of said first thermostating means and the temperature registered by
the temperature sensing means of said second thermostating means are
identical to one another and, consequently, identical to the deep body
temperature, T.sub.DBT.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be further described with reference to the
drawings, wherein
FIG. 1 diagrammatically shows an elevational, sectional view of a first
embodiment of an electrochemical measuring electrode device according to
the invention located on a skin surface,
FIG. 2 partly in elevational, sectional view a second embodiment of an
electrochemical measuring electrode device according to the invention,
FIG. 3 an exploded view of the second embodiment of the electrode device
according to the invention shown in FIG. 2,
FIG. 4 partly in elevational, sectional view a third embodiment of an
electrochemical measuring electrode device according to the invention,
FIG. 5 partly in elevational, sectional view a fourth embodiment of an
electrochemical measuring electrode device according to the invention,
FIG. 6 partly in elevational, sectional view a fifth embodiment of an
electrochemical measuring electrode device according to the invention,
FIG. 7 a detail of a further embodiment of an electrochemical measuring
electrode device according to the invention,
FIG. 8 a diagram showing the thermostating power generated in a
conventional measuring electrode device and in an electrochemical
measuring electrode device according to the invention, respectively, under
various test conditions,
FIG. 9 a diagram showing the temperature response, i.e. the temperature
rise and temperature decay, of a conventional electrochemical measuring
electrode device and of an electrochemical measuring electrode device
according to the invention,
FIG. 10 a diagram simultaneously showing a signal indicating the partial
pressure of oxygen measured by means of an electrochemical measuring
electrode device according to the invention and a signal indicating the
power generated in said electrode device,
FIG. 11 a diagram showing blood flow measuring results obtained by means of
the electrochemical measuring electrode device according to the invention
as compared to measuring results obtained simultaneously by counting the
.gamma.-emission from an Xe-133 dose, and
FIG. 12 a diagram showing test results obtained by means of the
electrochemical measuring electrode device according to the invention in
an experiment simulating the measurement of the deep body temperature,
T.sub.DBT.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 a first embodiment of an electrochemical measuring electrode
device according to the invention is shown in which the main components of
the electrode device are shown. The measuring electrode device designated
1 in its entirety is located at a skin surface shown schematically in FIG.
1 and designated 2. The electrode device 1 comprises an electrode housing
3 made of plastics, e.g. acrylonitrile-butadiene-styrene. The electrode
housing 3 is connected to a metallic body 4 of material showing high heat
conductivity, e.g. copper, the importance of which will be explained in
greater detail below. Furthermore, the electrode device comprises an
annular body 5 also made of plastics, e.g.
acrylonitrile-butadiene-styrene. The electrode housing 3 is provided with
a stub 6 adapted to cooperate with a multicore cable 7 the jacket of which
is shown in FIG. 1 and which is adapted to connect the electrode device to
external measuring equipment. On the metallic body 4 a thick film
substrate 8, of e.g. alumina, is located in thermal conductive connection
therewith. The substrate 8 is provided with thermostating means, i.e.
temperature measuring means and temperature controlling means, e.g. an
NTC-resistor and a heating resistor which may be constructed in thick film
technique on the substrate or provided as discrete components as will be
described in greater detail below. Furthermore, the electrode housing 3 is
provided with a cover, not shown, opposite to the metallic body 4 and the
thick film substrate 8. The interior space thus defined in the electrode
housing 3 is filled up with an appropriate filling material or casting,
e.g. an epoxy casting.
In a recess in the above mentioned annular body 5 a thick film substrate 10
of e.g. alumina is mounted which constitutes the sensor substrate in the
inventive measuring electrode device in accordance with the principles
described in Applicant's copending Danish patent applications No. 1650/81.
The substrate 10 being a substantially circular substrate has a
substantially plane upper surface as the substrate 8, which is a
substantially circular substrate having two opposite plane surfaces, and a
domed lower surface provided with a central protrusion 10a. Alternatively,
the substrates 8 and 10 may be identical, i.e. of the above described type
having a plane and a domed surface provided with a central protrusion. The
inner space defined within the annular body 5 between the lower surface of
the metallic body 4 and the upper surface of the substrate 10 is also
filled with an appropriate filling material or casting, e.g. an epoxy
casting. Before filling the interior spaces within the electrode housing 3
and within the annular body 5, the thermostating means located on the
upper substrate 8 and the components of the sensor substrate 10 are
connected through soldered joints to individual cores of the multicore
cable 7.
The embodiment of the invention shown in FIG. 1 is a polarographic
electrode device comprising an anode layer 11 and a cathode (not shown)
arranged in a through-going passage in the central protrusion 10a of the
sensor substrate 10 in a manner described in applicant's copending Danish
patent application No. 1650/81. Furthermore, the anode layer 11 being a
thick film silver layer is connected to a terminal field on the opposite
side of the substrate 10 by means of a leading through connection in a
manner also described in applicant's above mentioned Danish patent
applications.
In an external, circumferential recess in the annular body 5, an O-ring 13
is located which secures a gas permeable and liquid impermeable membrane
14 relative to the lower domed surface of the sensor substrate 10. The
membrane 14 may be made of e.g. polypropylene or tetrafluoroethylene. The
above mentioned central protrusion 10a of the sensor substrate 10
provides, in combination with the membrane 14, an electrolyte reservoir 15
for an electrolyte solution of the electrochemical measuring electrode
device.
The metallic body 4 is provided with external threads which are adapted to
cooperate with corresponding internal threads of an annular metallic body
16, preferably also made of a material showing high heat conductivity,
e.g. copper. Thus, the metallic body 16 is thermally connected to the
substrate 8 through the metallic body 4. As will be appreciated, the two
metallic bodies 4 and 16 constitute a metallic jacket enclosing the sensor
substrate of the electrode device. The jacket and the sensor substrate are
adapted to be thermostated by means of the thermostating means on the
substrate 8 and the thermostating means on the substrate 10, respectively.
As shown in FIG. 1 the annular metallic body 16 is mounted within an
annular fixing ring 17 made of a material showing excellent thermal
insulating qualities, e.g. plastics including
acrylonitrile-butadiene-styrene.
When in use, the sensor substrate 10 and thus the active surface of the
electrochemical measuring electrode device and the jacket, i.e. the
substrate 8 arranged in heat conductive connection with the metallic body
4 and the annular metallic body 16 are thermostatically heated to the same
temperature, e.g. 45.degree. C. The heating of the sensor substrate 10 and
the jacket to the same temperature provides that there is substantially no
net heat flow between the sensor substrate 10 and the jacket. Therefore,
the heat flux from the sensor substrate 10 is unidirectional, i.e. has a
downward direction to the skin surface below the active sensor surface of
the sensor substrate. Apart from virtually insulating the sensor substrate
10 totally relative to the environment, the jacket also contributes to the
heating of the skin surface below the electrode device in such a manner
that any heat flux from the sensor substrate 10 to any part of the skin
surface outside the jacket dimensions are virtually eliminated. Therefore,
the jacket provides a virtual heat jacket in relation to the skin surface
heated by the sensor substrate 10 so that the heat flow from the sensor
substrate 10 apart from being unidirectional becomes virtually
one-dimensional. This aspect is illustrated in FIG. 1 by a curve 18 (a, b,
c) which is shown indicating an isoterm, i.e. a curve drawn through
locations having identical temperature. As will be seen from FIG. 1, the
width of the uniformly heated skin surface is largely increased as
indicated by the outer branches of the curve (18a, 18b) relative to the
situation in which only the sensor surface, i.e. the substrate 10, is
thermostatically heated to a temperature above skin temperature (18c).
This largely increased and uniformly heated skin surface, in which
hyperemia is produced and which is obtained by means of the annular
metallic body 16 in heat conductive connection with the substrate 8 being
thermostatically heated to the same temperature as the sensor substrate
10, provides the excellent measuring results which may be obtained by
means of the electrochemical measuring electrode device according to the
invention as will be described in greater detail below.
In FIG. 2, a second embodiment of the electrochemical measuring electrode
device according to the invention is shown. The embodiment shown in FIG. 2
differs only slightly from the embodiment shown in FIG. 1 and therefore,
identical reference numerals are being used for identical parts. Thus, the
electrode housing 3 is provided with the protruding annular part
designated 3a, and the annular fixing ring 17 is provided with a covering
part 17a which covers the annular metallic body 16 which is mounted within
the fixing ring 17. In the embodiment shown in FIG. 2, the said annular
metallic body 16 is provided with an internal annular recess in which a
thermally insulating ring body 19 is located, which is made of e.g.
plastics including acrylonitrile-butadiene-styrene. In FIG. 2, several
individual cores 20a, 20b, 20c, 22a, 22b, 22c, 22d and 22e of the
multicore cable 7 are shown of which the cores 20a, 20b, and 20c are
connected to the components on the substrate 8 through soldered joints
21a, 21b, and 21c, respectively. The cores 22a, 22b, 22c, 22d, and 22e are
led through an aperture in the substrate 8 and an aperture in the metallic
body 4 and connected to components on the substrate 10 through soldered
joints 23a, 23b, 23c, 23d, and 23e, respectively.
In FIG. 3, an exploded view of the above described second embodiment of the
electrochemical measuring electrode device according to the invention is
shown. Starting from above, a cover 24 is shown which has been mentioned
above but which is not shown in FIGS. 1 or 2. Subsequently, the multicore
cable 7, the electrode housing 3, the substrate 8, the metallic body 4,
the annular body 5, the substrate 10, and the annular fixing ring 17 are
shown. In FIG. 3, the substrates 8 and 10 are shown in greater detail
compared to FIGS. 1 and 2. Thus, the thermostating means, i.e. the
temperature measuring means and the temperature controlling means of the
substrates 8 and 10, are shown. On the substrate 8, an NTC-resistor 25 and
a heating resistor 26 are applied in thick film technique. Analogously,
the substrate 10 is provided with an NTC-resistor 27 and a heating
resistor 28 and, furthermore, a terminal field 29 for connection to an
electrode of the sensor substrate of the electrochemical measuring
electrode device. The construction and configuration of the electrode as
well as the entire sensor substrate including thermostating means is
disclosed in the above mentioned Danish patent application No. 1650/81.
While the two above described embodiments of the electrochemical measuring
electrode device according to the invention, i.e. the embodiments shown in
FIG. 1 and in FIGS. 2 and 3, respectively, are adapted to be mounted
within the annular fixing ring 17, the embodiment of the invention shown
in FIG. 4 is adapted to be mounted within a conventional fixing ring.
Therefore, the electrode housing 3, the metallic body 4, the annular body
5, the annular metallic body 16, as shown in FIGS. 1-3, are omitted in
FIG. 4 and replaced by alternative components in order to permit mounting
of the electrode device shown in FIG. 4 in the said conventional fixing
ring. Instead of the metallic body 4 and the annular metallic body 16,
constituting the jacket in the above described embodiments, the embodiment
shown in FIG. 4 comprises a funnel-shaped metallic body or jacket 30 which
is mounted within an electrode housing 31 which constitutes both the
components 3 and 5 shown in FIGS. 1-3. Furthermore, the embodiment shown
in FIG. 4 comprises an annular body 32 which is mounted within an internal
recess in the funnel-shaped metallic body 30 and in an recess of which the
sensor substrate 10 is mounted. Apart from the above mentioned cores 20a,
20b, 20c, 22a, 22b, 22c, 22d, and 22e and the above mentioned
corresponding soldered joints 21a, 21b, 21c, 23a, 23b, 23c, 23d, and 23e,
a fourth core 20d and a corresponding soldered joint 21d of a component on
the substrate 8 are shown in FIG. 4.
In the embodiment of the invention shown in FIG. 4, the funnel-shaped
metallic body 30 and the substrate 8 may be replaced by a single
funnel-shaped body made of e.g. alumina which constitutes the jacket of
the electrochemical measuring electrode device. Thus, the funnel-shaped
body may be provided with a thick film component constructed on the
substrate 8 in the embodiment shown in FIG. 4.
In FIG. 5 a fourth embodiment of an electrochemical measuring electrode
device according to the invention is shown. Basically, the embodiment
shown in FIG. 5 differs from the embodiment shown in FIG. 4 in that the
total size or height of the electrode device including the fixing ring is
reduced radically. This is obtained by integration of the electrode
housing and the fixing ring.
Thus, the funnel-shaped metallic body or jacket 30 is mounted in a recess
in a funnel-shaped body 33 also constituting the cover of the electrode
device. The funnel-shaped body 33 may be made of e.g.
acrylonitrile-butadiene-styrene. The funnel-shaped body 33 is provided
with a circumferential groove which is adapted to cooperate, in a spring
catch, with an internal annular protrusion of a ring 34 which is also
provided with an external annular protrusion adapted to cooperate, in
another spring catch, with a corresponding circumferential groove in a
fixing ring 35 of conventional shape. The ring 34 and the fixing ring 35
are preferably made of plasticized polyvinyl chloride and pol | | |
