Method and an arrangement for continuously measuring the partial pressure of a gas in a sample

A method and an arrangement for continuously measuring the partial pressure of a gas in a sample, particularly of oxygen dissolved in blood flowing through muscle tissue which is covered by a skin layer, comprises a support probe which is adapted to be positioned intermediate the skin layer and a portion of the sample so that the probe is fixedly held in position against the sample portion. A polarographic cell is mounted on the probe and has a gas-measuring part which is in firm engagement with the sample portion so as to generate a signal indicative of the amount of gas being diffused from the sample portion. The polarographic cell is interchangeably and detachably mounted on the probe so as to facilitate sterilization of the various parts of the arrangement. A plurality of gas-measuring electrodes are utilized in combination with an indicating arrangement to either measure the distribution of the oxygen gas being diffused over an area of the sample portion or to measure the average value of gas being diffused from the latter.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and an arrangement for 
continuously measuring the partial pressure of a gas in a sample and, more 
particularly, to such a method and arrangement which measures the partial 
pressure of oxygen dissolved in blood flowing through muscle tissue which 
is covered by a skin layer. 
The partial pressure measurement of a gas such as oxygen in a sample of 
living tissue has recently become of growing medical significance. Recent 
technical developments have made it feasible to measure the amount of 
oxygen contained in the blood stream which actually flows to the cells of 
living tissue, i.e. at the end of the respiration chain, rather than 
relying on the standard technique of measuring the amount of oxygen which 
actually enters the lungs, i.e. at the beginning point of the respiration 
chain. 
Thus, it is known to measure the partial pressure of oxygen in blood 
vessels by using a cathetertype device or by using needle or so-called pin 
electrodes. Such measuring devices are known in the art and reference may 
be made to Zeitschrift Fuer Kreislaufforschung, 1971, pages 13- 23, or 
published German application DAS 1,179,393. 
It is also known to measure the partial pressure of oxygen in specific 
cells at specific locations in living tissue by using micro-needle 
electrodes (Garching Instrumente Prospekt, Naturwissenschaft 1972, page 
544). 
Furthermore, it is known to measure the partial pressure of oxygen by using 
polarographic-type devices which are placed on the outer skin layer of 
living tissue and are operative to receive and measure the amount of 
oxygen which diffuses through the skin layer. Such devices are also known 
in the art and reference may be made in this connection to published 
German applications DOS 2,145,400 or DOS 2,255,879. 
However, these prior-art techniques have not proven altogether satisfactory 
in obtaining measurement data to directly analyze the status of 
utilization of oxygen of the body by the oxygen partial pressure of its 
tissue. Recent experiments (Mikrozirkulation Workshop, April 1974, Volume 
5, page 36 ff.) indicate that the partial pressure of oxygen in living 
tissue is very much lower than in the blood vessels. This shows 
(publication of Max Planck Gesellschaft, 1974, pages 444-463)that the 
blood is used by the organism as a very large and very readily available 
butter supply of oxygen. The relatively large concentration gradient of 
oxygen between the blood vessels and the surrounding tissue is employed by 
the living organism for the adaptation of the microcirculation to the 
oxygen partial pressue as needed in the tissue. The ability to change the 
microcirculation is different to the various organs of the body. 
Especially the tissue of the skeleton muscles has a high range of 
adaptation of the microflow to the need for oxygen of the tissue, and the 
muscle tissue shows large changes in oxygen partial pressure related to 
the status of oxygen utilization of the body. Reference can be had to 
Microvascular Research, Volume 8, 1974/283. 
It is desirable to accurately measure the partial pressure of oxygen 
flowing in the blood stream of skeletal muscle tissue. This is 
particularly true in case of impending hypoxia, wherein the flow of oxygen 
quickly varies from moment to moment. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general object of the present invention to overcome 
the disadvantages of the prior art. 
Another object of the invention is to accurately measure the partial 
pressure of a gas such as oxygen in a sample, such as muscle tissue 
covered by a skin layer. 
An additional object of the present invention is to provide a universally 
applicable arrangement for measuring the partial pressure of a gas such as 
oxygen which is compact in construction and simple in manufacture. 
Still a further object of the invention is to provide a reliable method for 
accurately measuring the partial pressure of gas in a sample. 
In keeping with these objects and others which will become apparent 
hereinafter one feature of the invention, briefly stated, is embodied in a 
method and an arrangement for continuously measuring the partial pressure 
of a gas in a sample, particularly of oxygen dissolved in blood flowing 
through a muscle tissue which is covered by a skin layer, which comprises 
a support probe having first and second probe sections which are adapted 
to be positioned intermediate the skin layer and a portion of the sample 
so that the probe is fixedly held in position against the sample portion. 
The support probe is so positioned by incising the skin layer and 
inserting the probe through the incision. Furthermore, a polarographic 
cell is mounted, preferably in an interchangeable and detachable manner, 
at one of the probe sections and has a gas-measuring part which is 
positioned so as to be in firm engagement with the sample portion to be 
measured. The cell has electrodes which are in electrolytic contact with 
each other so as to generate a signal which is indicative of the amount of 
gas being diffused from the sample portion. 
In accordance with the invention, the gas-measuring polarographic cell at 
the lower end region of the support 2 which is placed in contact with the 
sample to be measured will cooperate with sensitive indicating devices and 
thereby strongly indicate to a user, even small changes in the transport 
rate of oxygen flowing in the blood stream. This information is especially 
useful in obtaining a quick and early recognition of the moment of danger 
for a patient, thus making possible the quick introduction of appropriate 
medical countermeasures. 
In accordance with another feature of the invention, the polarographic cell 
is interchangeable and detachably mounted at the lower end region of the 
support probe. This feature assures efficient maintenance for purposes of 
sterilization and/or the replacement of nonoperative parts. 
Furthermore, the support probe has a tapered configuration so that its wall 
surfaces are placed in sealing engagement with the underside of the outer 
skin layer and the upper surface of the sample to be measured. This 
feature permits the polarographic cell which is mounted on the probe to be 
firmly held in position on the sample, thus leading to a substanial 
reduction of measurement errors caused by undesirable shifting of the 
position of the polarographic cell on the sample. 
In accordance with yet another feature of the invention, the polarographic 
cell comprises a plurality of gas-measuring sensor electrodes which are 
operative for measuring the distribution of the oxygen pressure 
measurements over an entire surface region of the sample. Each oxygen 
pressure measurement can be seperately indicated by a respective 
indicating device. 
Alternatively, each partial pressure measurement of oxygen can be combined 
in a noiseless summing amplifier so as to indicate the total mean value of 
oxygen in the sample portion. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring jointly to the method and arrangement for continuously measuring 
the partial pressure of a gas in a sample as illustrated in the drawing, 
it will be seen that reference numeral 5 generally identifies a sample 
which contains the gas whose partial pressure is to be measured. The 
sample is muscle tissue which is covered by an exterior skin layer 4. 
As shown in FIG. 1 an incision 40 preferably only a few millimeters wide is 
formed in the skin 4. A probe 2 is thereupon inserted through the incision 
40 so that one contact surface of the probe 2 engages the underside of the 
skin layer 4, and so that another contact surface of the probe 2 engages 
upper surface 50 of the muscle tissue 5. These tapered surfaces of the 
probe serve to fixedly hold the probe 2 in position against the muscle 
tissue 5 and in sealing engagement with the latter and with the skin layer 
4. 
At the other contact of the probe 2, i.e. the surface which faces and 
engages the muscle tissue 5, a polarographic cell 1 is mounted on the 
probe 2. As shown in the enlarged view of FIG. 2, the polarographic cell 
comprises at least one and preferably a plurality of gas-measuring sensor 
electrodes or so-called polarized electrodes 121, 122, 123 . . . 124 (only 
four sensor electrodes being shown for the sake of clarity), each sensor 
electrode having a cross-sectional diameter of at least 10 microns and at 
most 20 microns. The sensor electrodes are all spaced from each other in 
electrically-insulating relationship and are embedded within a glass 
carrier 12. The sensor electrodes are generally constituted of platinum 
metal material. 
An annular reference or so-called non-polarized electrode 11 is constituted 
of metal material, and preferably silver chloride coated silver material. 
Reference electrode 11 surrounds the lass carrier 12. 
An annular casing or housing 10 preferably constituted of synthetic plastic 
material surrounds the reference electrode 11. At the periphery of the 
upper end region of housing 10, a flange part is formed which is adapted 
to be interchangeably and detachably lodged in recess 21 formed in the 
support probe 2. 
The housing 10 is also formed with a groove 101 adjacent the flange part so 
as to receive a corresponding projection of the support probe 2. By virtue 
of the yieldable nature of the synthetic plastic material casing and of 
the support probe 2 which is preferably constituted of elastic, silicon 
rubber, the polarographic cell 1 is securely held in position on the probe 
2. 
The polarographic cell 1 also comprises a space 15 in which the electrolyte 
(not illustrated for the sake of clarity), preferably potassium chloride 
and water, is contained. A gas-permeable membrane 13 overlies space 15 and 
prevents the electrolyte from escaping from the polarographic cell 1 by 
sealing means 14, preferably an elastic O-ring seal. 
A cover 16, preferably constituted of synthetic plastic material or teflon 
material is centrally and inwardly located with respect to the housing 10 
and overlies the reference electrode and the glass carrier 12 which 
contains the sensor electrodes 121 - 124. The cover 16 is interchangeably 
and detachably mounted to the polarographic cell 1 by means of the 
illustrated screw. 
In operation, the reference electrode 11 and at least one of the sensor 
electrodes react in the presence of the electrolyte with the oxygen gas 
which is being diffused from the sample portion 5 and through the 
gas-permeable membrane 13. An electrical signal is thereby generated which 
is indicative of the partial pressure of oxygen in the sample. The signal 
is thereupon conducted to the illustrated indicating devices by means of 
electrial conductors or wires 1210 . . . 1250 (only electrical wires 1210, 
1240 and 1250 have been illustrated for the sake of clarity). However, it 
will be understood that additional electrical wires can be electrically 
connected to other sensor electrodes, such as electrodes 122 and 123. 
In order to relieve any possible stress on the illustrated electrical wires 
1210 and 1240, stress-reducing lugs 161 and 162 are mounted on or are 
integral with the cover 16. Upper stress-relief lugs 161 and lower lugs 
162 are formed with passages which cooperate with additional passages 
formed in the cover 16 so as to guide the respective electrical wires in a 
path towards the interior passage of the flexible tubular section 22 of 
the support probe 2. The lugs 161 and 162 may be formed of any suitable 
material, such as synthetic plastic material or of teflon strands. The 
flexible tubular section 22 is only partially shown in the drawing and 
essentially protects and maintains the electrical wires in place during 
the positioning of the polarographic cell on the sample portion. 
The indicating devices are arranged at the other end of the elongated 
tubular section 22, i.e. the end which faces away from the polarographic 
cell 1. As diagrammatically illustrated in FIG. 2, the indicating devices 
are connected in two seperate modes depending upon the position of the 
switches S.sub.121 and S.sub.124. If these switches are in position A, 
then the respective signals generated by electrodes 121 and 124, for 
example, are respectively conducted via wires 1210 and 1240 to indicating 
devices I.sub.121 and I.sub.124. Conductive wire 1250 completes the 
electrical circuit. In this position of the switches, the distribution of 
the partial pressure measurement of oxygen as measured over an area of the 
sample portion is obtained simply by observing the reading of the various 
indicating devices I.sub.121 and I.sub.124. It will be understood that 
more than the two illustrated indicating devices I.sub.121 and I.sub.124 
can also be employed. 
Alternatively, if the switches are placed in position B, then the 
respective electrical signals are conducted via wires 1210 and 1240 to the 
summing amplifier, wherein the respective signals are combined in any 
desired manner. For example, the respective signals can be combined so 
that a single average or mean value of all of the respective electrical 
signals is indicated on indicating device I. 
A further feature of the invention is the provision of a stress-reducing 
lug 163 which is centrally located at the upper surface of cover 16. A 
thread 164, preferably of nylon material, is attached to lug 163 to 
relieve of possible stress to the wires 1210, 1240, 1250. 
Thus, in accordance with the invention, the polarographic cell is easy to 
mount and dismount from the resilient and elastic support probe 2. By 
constituting the probe 2 of silicon rubber material, the probe is 
relatively simple to disinfect after each use. It is further desirable to 
configurate the probe in an annular, disk-shaped configuration or in a 
substantially circular configuration having a cross-sectional diameter of 
at least 20 and at most 35 mm. Using these dimensions for the probe, it is 
desirable to also shape the polarographic cell 1 to have an annular 
configuration which has a diameter of at least 10 and at most 15 mm. Of 
course, it will be understood that other configurations are also possible 
for the probe and the polarographic cell. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
method and an arrangement for continuously measuring the partial pressure 
of a gas in a sample, it is not intended to be limited to the details 
shown, since various modifications and structural changes may be made 
without departing in any way from the spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.