Cathode for polarographic measurements in physiological medium

A cathode for polarographic measurements in physiological medium, such as measuring oxygen partial pressure in a human or animal body, is comprised of an elongated cable having a conductive filament, such as a steel wire or a carbon fiber enveloped within an insulating material, such as a layer of polyurethane and sheated in a body-tolerable insulating material, such as a layer of polytetrafluoroethylene. The proximal end of the conductive filament is coated with a layer of a precious metal, such as gold or platinum, and the front face of the cable is provided with a layer of an oxygen-permeable electrically conductive membrane, such as composed of polymethylacrylate or polystyrene. The distal end of the conductive filament is connected to an electrical source, a signal display means and/or a signal processing means.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to cathode structures and somewhat more particularly 
to polarographic cathode structures useful in physiological mediums. 
2. Prior Art 
S. Sinmaru et al. in an article entitled "Catheter-Mounted Oxygen Electrode 
For Monitoring Oxygen Tension", appearing in "Cardiovascular Research 
Center Bulletin", April-June 1972, page 112, describe a cathode for 
polarographic measurements comprised of a steel wire having a piece of a 
gold wire attached to the proximal tip of the steel wire. The steel wire 
with the attached gold wire is coated or sealed within an insulating 
material and this insulating envelope is further sheated in a layer of a 
body-tolerable material. The proximal tip of the gold wire is covered with 
an oxygen-permeable membrane and contacts the physiological medium. The 
manufacture of this type of polarographic cathode structure is 
complicated. Each steel wire piece must be individually connected to a 
gold wire piece, for example, by spot welding. Accordingly, such cathodes 
are comparatively expensive. 
Another known polarographic cathode structure is comprised of a cable 
section having at least one continuous strand of a precious-metal wire 
therein, preferably a gold wire, which is enveloped in an insulating 
material. In the manufacture of this type of cathode structure, cut 
sections or pieces of an insulated precious metal cable are utilized. 
Cathode structures of this type have proven successful for polarographic 
measurement in physiological medium. The manufacture of this type of 
cathode structure is relatively simple. However, because of the need for 
continuous gold wires, these cathodes are relatively expensive. Economical 
considerations play a major role in the use of such cathodes which, for 
medical reasons, are preferably developed as throw-away articles or as 
articles of one-time use. Further, gold wires having small diameters are 
mechanically weak so that special care is required during the manufacture 
and handling of cathodes containing such gold wires. 
SUMMARY OF THE INVENTION 
The invention provides a polarographic cathode structure for use in 
physiological medium and which avoids or at least minimizes the above 
prior art drawbacks. 
Cathodes constructed in accordance with the principles of the invention 
function to measure polarographic data in physiological medium at least as 
well as the prior art structures but are substantially more economical and 
may be employed as throw-away articles which have adequate mechanical 
properties for problem-free handling. 
In accordance with the principles of the invention, a cathode structure is 
comprised of a continuous filament composed of a conductive non-precious 
material, such as steel or carbon, having a front end face thereof coated 
with a thin layer of a precious metal, such as gold or platinum and which 
is enveloped in an insulating material. The precious metal layer may be 
applied, for example, to the frontal end face of a steel wire by a 
controlled electrolytic deposition process so that a select layer 
thickness is readily achieved. Further, a plurality of conductive 
filaments or wires may be simultaneously provided with, for example, a 
gold layer via the electrolytic deposition process for improved economy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention provides a cathode for polarographic measurement in 
physiological medium, such as for measuring oxygen partial pressure in 
human or animal bodies as well as a method of manufacturing such cathodes. 
Cathodes constructed in accordance with the principles of the invention may 
be operationally coupled at their distal end via an operational circuit to 
an electrical source and to a signal display means and/or a signal 
processing means. The proximal end of such cathodes may be covered with an 
oxygen-permeable electrically conductive membrane and many be 
operationally connected to an anode via the physiological medium. 
As shown on the drawing, a cathode construction in accordance with the 
principles of the invention may be comprised of an elongated (basically 
round) conductive cable piece or section having an elongated conductor or 
wire 1 which includes a proximal end 1' and a distal end 1" and is 
enveloped by an insulating envelope 2, which is absent from the distal and 
proximal ends of the conductor. The filament or wire 1 is composed of a 
common or non-precious conductive material, such as steel or carbon and 
has a diameter in the order of magnitude of about 10 to 100 .mu.m and, in 
an exemplary embodiment has a preferred diameter of about 60 .mu.m. The 
insulating envelope 2 may be composed of a suitable dielectric 
lacquer-like material, for example, polyurethane. The fragmentary 
components of the basic cable may comprise select length pieces or 
sections cut from longer, for example, steel wire, insulated cables 
(commercially available in any desired lengths) which may be continuously 
manufactured in a conventional manner. 
A relatively thin layer 3 composed of a precious or noble metal is applied 
onto the front surface of the proximal end 1' of filament 1. The layer 3 
is composed, for example, of gold or platinum or some other noble metal 
and preferably has a thickness of several micrometers. The precious metal 
layer 3 may be applied in a controlled manner, for example, by an 
electrolytic deposition process and may be simultaneously applied to a 
large number of suitable cable sections. 
The basic cable section, comprised of elements 1 and 2 having a thin, for 
example, gold layer 3 on a front end face of element 1, is provided with 
an external sheathing 4 composed of a body-tolerable material, such as 
polytetrafluoroethylene. 
An oxygen-permeable electrically conductive membrane 5 is applied over the 
entire proximal end of the cathode as shown. The membrane 5 may be 
applied, for example, by dipping or immersing a gold-coated steel wire 
proximal end into a bath composed of a material forming the membrane. 
Preferably, the membrane is composed of materials which are hydrophilic 
and only porous to relatively small molecules and/or ions but non-porous 
to macromolecules, such as proteins. Preferably, the membrane 5 is 
composed of a material selected from the group consisting of cross-linked 
polymethylacrylate, polystyrene and cellulose acetate. 
The distal end 1" of filament 1 is operationally coupled (for example, by 
soldering or via a suitable connector of sleeve) via an electrical lead 6 
to a means S which provides an electrical potential to the cathode from a 
suitable electrical source and which measures, displays or otherwise 
processes the polarographic signals received from the cathode. Means S is 
shown as being provided with another electrical lead 6' which may be 
coupled to the patient P via an anode so as to complete an operational 
electrical circuit. 
As indicated earlier, other combinations of a wire or filament composed of 
a non-precious electrically conductive material having a layer of a 
precious metal applied onto a proximal front end face of the wire may also 
be utilized in constructing cathodes in accordance with the principles of 
the invention. An exemplary embodiment of such other combination is a 
carbon fiber coated at an end face thereof with platinum. 
The savings in material cost of previous metal and the savings in 
manufacturing costs realized by constructing cathodes in accordance with 
the principles of the invention are considerable relative to prior art 
cathodes, such as discussed earlier. Further, the mechanical stability or 
strength during manufacturing and/or handling of cathodes having a 
construction in accordance with the principles of the invention is good. 
The method embodiments of the invention generally comprise (1) providing a 
select length of an elongated conductive cable having an insulating 
envelope about an electrically conductive filament having at least one end 
face thereof free of the insulating envelope; (2) coating a thin layer of 
a precious metal onto the end face of the conductive filament; (3) 
applying a layer of a body-tolerable material about only the insulating 
envelope; and (4) applying a layer of an oxygen-permeable conductive 
material onto the entire end portion of the resultant structure, i.e., a 
so-coated filament end, adjacent insulating envelope end surface and the 
adjacent end surface of the layer composed of the body-tolerable layer. In 
certain embodiments, the initially provided cable may include an outer 
layer of a body-tolerable material about the insulating layer so that step 
(3) may be omitted and/or combined with step (1). 
In a preferred method, the first step of the method may comprise cutting or 
otherwise severing a plurality of individual select length cables from a 
suitable cable supply, as a reel having an unlimited length of suitable 
cable thereon. In this manner, any number of select length cable pieces 
may be simultaneously produced for improved manufacturing efficiency. 
In a preferred method, the second step of method may comprise applying the 
thin layer of a precious metal onto an end face of the conductive filament 
via a controlled electrolytic deposition process. For example, a plurality 
of select length cable pieces having an uncovered filament end may be 
positioned within a suitable electrolytic bath and a thin layer of a 
precious metal be electrolytically deposited or plated onto each filament 
end. 
In like fashion, the body-tolerable material may be simultaneously applied 
to a plurality of cable sections or pieces in instances where the initial 
cable lacks a layer of such material. 
In a preferred method, the fourth step of the method may comprise applying 
the layer of oxygen-permeable conductive material onto the end of the 
cable having a layer of precious or noble metal on the filament end 
thereof via dipping or immersing one or a plurality of, for example, 
gold-coated ends of steel wire, into a bath containing an oxygen-permeable 
conductive material, which preferably is selected from the group 
consisting of cross-linked polymethylacrylate, polystyrene and cellulose 
acetate. 
As is apparent from the foregoing specification, the present invention is 
susceptible of being embodied with various alterations and modifications 
which may differ particularly from those that have been described in the 
preceding specification and description. For this reason, it is to be 
fully understood that all of the foregoing is intended to be merely 
illustrative and is not to be construed or interpreted as being 
restrictive or otherwise limiting of the present invention, excepting as 
it is set forth and defined in the hereto-appended claims.