Non-invasive measurement of skin blood flow: comparison between plethysmography, laser-Doppler flowmeter and heat thermal clearance method.

A comparison was made between (a) a new probe measuring heat thermal (HTC), (b) plethysmography and (c) a Laser-Doppler (LDF) technique during changes in skin blood flow (SkBF) on six subjects, each participating in a single experiment. Increase of SkBF was induced by heating the body skin with an electric cover. Heat thermal clearance correlated well with the forearm blood flow (FBF) (r = 0.69-0.97) and with LDF measurements (r = 0.86-0.92) in each experiment, Laser-Doppler flowmeter also correlated well with FBF (r = 0.73-0.97). However, the relationship between HTC, LDF and FBF varied from one experiment to another. Values for HTC and for LDF at zero FBF, extrapolated from the regression relationships, ranged from 6.438 to 10.919 k, and from -0.37 to +0.17 volt respectively. The value for HTC at zero LDF extrapolated from the regression relationships ranged from 4.109 to 12.413 k. Values for HTC and LDF when blood flow to the arm was mechanically occluded ranged from 5.17 to 10.71 k and from 0.07 to 0.24 volt respectively. Thus HTC, LDF and FBF measurement of SkBF appear to produce the same response pattern during reflex cutaneous vasodilatation. Each of these three methods measured SkBF in different skin areas and at different depths in the skin, which might also explain the variability in their relationship.