Laser-Doppler and plethysmographic skin blood flow during exercise and during acute heat stress in the sauna.

Forearm skin blood flow was measured in six male subjects by laser-Doppler flowmetry (LDF) and venous occlusion plethysmography (VOP) during constant-load (125-200 W) upright bicycle exercise in a warm environment (X + SD, ta 34.6 +/- 0.2 degrees C) and during a 15 min sauna bath (ta 69.0 +/- 2.8 degrees C). During the sauna test the LDF values correlated well with the VOP measurements in the initial phase of active cutaneous vasodilation, after which the LDF values almost leveled off in spite of a steady increase in VOP measurements. During the exercise the mean VOP and LDF values rose in parallel with each other to steady state levels. The relationship between the results of the two methods proved to be nonlinear. It was concluded that different parameters were measured by VOP and LDF. The latter measured mainly the integrated velocity of blood flow in the outermost cutaneous tissue, and this velocity seemed to be partly dependent on the level of the arterial inflow (VOP), but also on the prevailing pressure-flow and pressure-volume relations in the cutaneous vascular bed.