The spatial correlation of fluctuations of the blood flow in forearm skin

The oxygen tension at the skin surface, with the atmospheric oxygen supply excluded, may be measured polarographically on the human forearm. Under suitable environmental conditions, spontaneous fluctuations in skin surface oxygen tension can be recorded and these are the result of fluctuating blood flow in the superficial skin vessels. An array of separate cathodes in a single polarographic electrode assembly has been used to measure the fluctuations in blood flow which are occurring simultaneously at seven different points in the skin. Spectral analysis of a long recording of such fluctuations shows that most of the power is concentrated at the lower frequencies but does not reveal any clearly defined dominant frequency. It is clear, however, from inspection of the fluctuation patterns, that recurring bursts of activity occur with quite well-defined periodicities in the range of 30s to 5 min. There is a stronger correlation between the fluctuations occurring at points on the skin surface less than 1 mm apart than between points further apart, although there are clearly some components which are common to points separated by up to 5 mm which was the largest separation of cathodes used in these experiments. These observations are supported by the value of cross correlation coefficients between the channels. These results suggest that the observed fluctuations are the result of at least two factors. The first one is common to all the channels but the effect of this may be overridden by a second and more local one controlling the blood flow.