Surgery – Diagnostic testing
Patent
1995-01-30
1998-11-03
Nasser, Robert L.
Surgery
Diagnostic testing
600485, 600481, 600504, 600500, 600561, 600549, 600309, 600322, A61B 500
Patent
active
058301291
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for measuring the blood flow in or through an organ, particularly in human tissue, employing the hydrogen clearance method, and suitable means for performing this process.
2. Background and Material Information
Processes and measuring instruments for measurement of blood flow through an organ are known in the medical field and function both as a diagnostic tool, as well as for monitoring of the course and success of therapy or of a surgical operation. In known processes, the blood of the subject is enriched with hydrogen and used as an electrolyte, and two electrodes are introduced into the tissue to be studied to form a galvanic element. The electrical voltage of this element is related to the concentration of the hydrogen in the blood, among other factors. Hydrogen is mixed with air and introduced into the blood via the respiratory tract or, alternatively, hydrogen may be injected directly into the blood stream. As soon as the voltage between the electrodes has attained a predetermined limit value, the delivery of hydrogen is discontinued and a decrease in voltage as a function of time is observed. The slope of the measured curve of this function is representative of a measure for the tissue blood flow, in which the hydrogen-enriched blood is removed and replaced by hydrogen-free blood. The theoretical bases of this process, and in particular the calculation of the potentials of the electrodes as a function of the hydrogen ion concentration with the aid of Nernst's equation and the determination of the blood flow of a tissue volume from the decrease in concentration of the hydrogen in the blood with the aid of diffusion principles, are described in detail, for instance by K. Auckland et al, in Circulation Research, Vol. 14, 1964, pp. 164 ff.
Although determining the blood flow of tissue with the aid of inert gases such as hydrogen has been known for at least 40 years and has been discussed in many publications, the practical application of this process was previously limited to animal experimentation, or to measuring the blood flow rate at the tip of the little finger of a human being. The reasons for this are simple. With the equipment previously used to perform the process described, evaluatable and reproducible measurements could be obtained only if the current intensity between the electrodes and hence in the blood as well, that is, in the tissue to be studied, was at least 1.times.10.sup.-6 A, a value which is physiologically objectionable or even impermissible for some tissues.
One such measuring instrument is described, for instance, in the article entitled "H.sub.2 Clearance Measurement of Blood Flow: A Review of Technique and Polarographic Principles", Wise Young, in STROKE, Vol. 11, No. 5, September-October 1980, pp. 552-564.
An apparatus with which, for the first time, the determination of tissue blood flow by the advantageous hydrogen clearance method can be used without the requirement for a measuring current that is physiologically objectionable for human beings, is described in European Patent Application 0 452 276, for example.
Although the process described in EP 0 452 276 is a suitable method for measuring the blood flow in human tissue, it has been found in practice that, during long-term measurements, the highly sensitive electrodes required for this process relatively quickly either become coated with endogenous (especially fibrin-containing) substances, or oxidize, thereby impairing the accuracy of blood flow measurements made over a long period of time.
Another problem arises in the measurement of the spatial distribution of the blood flow in the tissue to be studied, which is especially desirable for long-term measurements. In such a measurement, multiple sensors are introduced into the tissue at multiple spatially separated points. If usable results are to be attained, several measuring instruments are required, and this undesirably raises the cost of the procedure for evaluation of
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Baer Hans
Flueckiger Daniel
Hirsbrunner Eduard
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