Correlation between blood volume and opacity changes in the finger.

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Abstract
A comparison was made between finger blood volume changes as measured by water plethysmography and simultaneously recorded photoelectric finger opacity changes. It was shown that: a quantitative correlation between the digital blood volume and opacity changes does not exist although the general pattern of the simultaneous records is usually similar; in some cases the digital blood volume increased while opacity decreased, or vice versa; the finger opacity pulsations were only slightly attenuated when total digital blood volume was kept constant (and blood color changes were excluded). The photo-electrically recorded opacity changes are not quantitatively (or even qualitatively) related to blood volume changes. An interpretation of the results, on the basis of differences in blood distribution between different vessels, is suggested.