Microcirculation and O2 Exchange through the Skin Surface: A Theoretical Analysis
Oxygen is supplied to the upper layers of the human skin not only by blood, but also by surrounding air. Already in 1851 Gerlach measured this O2 uptake by glueing a horse bladder on the human skin (Gerlach (1851)). The bladder was made gas-tight by varnishing. He found that during a period of 24 hours the O2 concentration in the bladder decreased from 21.0% to 19.02%, whereas at the same time the CO2 concentration increased from 0% to 2.5%. He followed from his experiments that “the cutaneous respiration (i.e. the O2 uptake from the surrounding air) depends on the amount of blood which perfuses the uppermost capillaries and on its flow velocity. All that increases the amount of blood within the skin increases the cutaneous respiration.” To analyse the O2 supply of the different layers of the skin pO2 profiles perpendicularly to the skin surface have been measured (Baumgärtl et al. (1987). They reveal that there is a competition between the O2 supply by blood and that by surrounding air. Starting with the pO2 of the surrounding air tissue pO2 first decreases, reaches a minimum and then increases. This demonstrates that the upper part of the skin up to the pO2 minimum is supplied by the O2 of the air, i.e. by the O2 flux through the epidermis, whereas the other parts receive their O2 from the blood. The oxygen uptake from the air amounts to 80–100 ml O2/(m2·h), i.e. a human being with a skin surface of 1.5 m2 has an O2 uptake of 2.0–2.5 ml O2/min or of about 1% of its resting O2 uptake (Fitzgerald (1957). For the total organism it is a small amount, but it can be important for the oxygen supply of the skin.
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