Much of the knowledge we have today about oxygen transport to tissue was gained by the use of polarographic oxygen electrodes. It was the development of the membrane-covered electrode by Clark in 1956 that opened up the field of in vivo physiological and indeed clinical measurements of oxygen in tissue. Certainly the early years of the ISOTT meetings were dominated by developments and applications of such oxygen (and hydrogen) electrodes.
New measurement and imaging techniques have now supplanted the polarographic electrode to a large extent. However, in order to interpret some of the measurements made using these new techniques it is very important not to overlook those physiological principles of oxygen supply to tissue that were so painstakingly established through the application of polarographic electrodes. The advantage of the electrode technique for the measurement of oxygen partial pressure is its resolution. It is possible to make measurements on the scale of microns, which means that the real heterogeneity of oxygen supply can be quantified. This, however, has also proved to be a disadvantage in that the question was always asked: How applicable is a measurement in a small area of tissue to the situation in the whole organ? To some extent this criticism was overcome with the use of multiple measurements with stepped needle electrodes or multi-channel surface electrodes to record pO2 histograms.
An alternative approach to making tissue measurements more useful clinically was to 'arterialize' the site of measurement by heating. This is the basis of transcutaneous measurement of pO2 which is a technique that continues to be used for some monitoring and tissue viability applications.
It is the ability to measure the distribution of pO2 in tissue that continues to make the oxygen electrode a useful tool both in understanding the physiology of oxygen supply and in measuring oxygen clinically in tissue. It is not usually the mean value of pO2 in an area of tissue that is important, but the degree of hypoxia, and this is best assessed from the pO2 histogram. This is particularly true in tumours and tissue viability assessments.
It is the intention of this review to examine the role of the oxygen electrode in the twenty first century by illustrating recent contributions to physiological knowledge and clinical applications. A concrete example of this is important new insight into the mechanism of oxygen supply to and within the skin, which has been achieved by the combined use of oxygen electrodes and 2 dimensional optical imaging of oxygen flux.
In preparing the review, I have been greatly helped by Horst Baumgärtl, Martina Günderoth, Dietrich Lübbers and Markus Stücker, to whom I am most grateful.
Harrison DK. Physiological oxygen measurements using oxygen electrodes. Adv Exp Med Biol 2002; 510: 163-168.
Dr. David K. Harrison, Durham Unit, Durham. Tel: +44 (0)191-333-2215.
Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, NE7 7DN, UK.
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