We compared laser-Doppler velocimetry with plethysmographically determined changes in skin blood flow (SkBF) in five studies on four men. Increments in SkBF were induced by raising whole-body skin temperature to 39 degrees C for 50-70 min. We found laser-Doppler blood flow (LDF) to correlate well with total forearm blood flow (FBF) within each study (r = 0.94-0.98), but the relationship varied among studies. Thus the slopes for the LDF vs. FBF relationship varied from 40 to 122 mV X ml-1 X 100 ml X min. The value for LDF at zero FBF, extrapolated from the regression relationships, ranged from 246 to 599 mV above the value for LDF set with the probe on a stationary object. The value for LDF when blood flow to the arm was mechanically occluded ranged from 110 to 230 mV. In a second series, we measured the LDF values from six sites on forearms of each of four normothermic men. There was marked regional variation, with 1.8- to 5.7-fold ranges in LDF within a given subject. Values for LDF during occlusion of the forearm were more consistent within and between subjects. Thus LDF appears to provide a good indicator of the response pattern of SkBF from the region of illuminated skin. However, variability in the relationship to total SkBF (probably arising from variation in the number of perfused capillaries in the small volume of tissue) and uncertainties in the value of LDF at zero SkBF make quantitative use difficult.

These findings preclude the interchange of readings by the 2 methods. Caution must be exercised in the diagnosis of hypertension when an automated device is used.

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