Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1998-07-22
2000-05-30
Tung, T.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204406, 204415, G01N 27404
Patent
active
060687436
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to measuring apparatus to determine the partial oxygen pressure in human brain tissue using a probe having a thin flexible tube made of a tissue-compatible plastic enclosing a volume filled with electrolyte and housing a polaragraphic cathode and an anode, the tube being oxygen permeable at least in a measurement zone, the probes being connected to a measuring apparatus.
BACKGROUND OF THE INVENTION
From the following documents, namely thin flexible catheter probe of the Clark type.
From the following documents, namely measurements"], W. Mundt, Clarik type pO.sub.2 probe suitable for this purpose.
Using appropriate emplacement techniques such as are described in the post-published patent application DE 195 02 183.5, such probes can be freely placed in the brain. Because of their small diameters and high flexibilities, such probes are suitable for long-term measurements in the brain tissue and in other susceptible body tissues. They are able to follow tissue movement (pulse, breathing) without hampering such movements and apply only slight pressure effects on the surrounding tissue, and as a result the oxygen supply is not adversely affected in the measurement process.
On the other hand, such extremely thin probes have drawbacks because their slight dimensions affect the implementability of long-term measurements.
Typically, a probe of the above type has an inside diameter of a few tenths of a mm and a length of several tens of cm. Consequently, the inner space to be filled with electrolyte is of the order of a few mm.sup.3, of which however only a small portion is available in the zone of the tiny cathode surface Such a small electrolyte supply is unusually low for PO.sub.2 probes of the Clark type and this constitutes a drawback for long-term measurements.
Clark type pO.sub.2 probes subject an electrolyte space to the ambient oxygen by means of an oxygen diffusion membrane. The oxygen diffuses through the membrane against the diffusion impedance. The quantity of oxygen per unit time entering the electrolyte depends on the ambient partial oxygen pressure. The entering oxygen is reduced by two electrodes, namely a cathode made of a suitable noble metal and an anode typically of silver, optionally with a silver oxide surface. The resulting current (measuring apparatus current) unambiguously depends on the in-diffusing oxygen, that is the ambient partial oxygen pressure. An appropriate polarographic potential must be applied to the electrodes.
Salt solutions, usually sodium chloride, are used as the electrolyte. Hydroxide is generated in the reduction of oxygen. Anodic silver goes into solution as silver salt. Silver is indeed amply present at the anode. On the other hand, the tiny supply of electrolyte of the probes being discussed is consumed comparatively quickly. The electrochemical equilibria change, and the relationship between the measuring current and the incoming flow of oxygen changes. When this occurs, the measurement must be stopped and the probe must be replaced. Electrolyte replenishment at the site, that is in the tissue, is impossible.
The problem of electrolyte consumption is described for probes of this kind in the German periodical Rommel however is unsuited for probes used in the brain because of the required minute diameter and high flexibility, and moreover such a system can only sense the electrolyte consumption but not eliminate it.
A medical pO.sub.2 probe is known from the British periodical does not comprise the membrane rigorously permeable only to gases, but a polyurethane membrane. This material is water-permeable, as indeed required in this design, in order to soak the electrolyte salt which is present in dry form under the membrane. Because the membrane, however, is also ion-permeable, the probe responds to the ambient pH and measuring is possible only at constant ambient pH. Therefore, the measurements are to be carried out in a phosphate buffered solution. This probe is poorly suited for medical purposes because it responds to a
REFERENCES:
patent: 4532013 (1985-07-01), Dietz et al.
patent: 4705617 (1987-11-01), Beebe et al.
patent: 4950378 (1990-08-01), Nagata
patent: 5352349 (1994-10-01), Inamoto et al.
Fujito Yuko et al, Galvanic Cell Type Oxygen Sensor, European Patent Office, Patent Abstracts of Japan, pub. No. 60093343 of May 25, 1985, appl. 58201973 filed Oct. 27, 1983, Japan Storage Battery Co. Ltd.
Farley Walter C.
Tung T.
LandOfFree
Brain-pO.sub.2 measuring device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Brain-pO.sub.2 measuring device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Brain-pO.sub.2 measuring device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1907740