Simultaneous assessment of red cell perfusion in skeletal muscle by laser Doppler flowmetry and video microscopy.

The objective of this study was to compare temporal and spatial variations of the laser Doppler flowmeter output (V) with the corresponding variations of perfusion (cells/mm3 X mm/s) evaluated by video microscopy. The flowmetry and video microscopy sampled 2 mm3 (approx.) and 0.84 mm3 surface volumes of the sartorius muscle in anesthetized frogs, respectively. The overall ranges of the output and perfusion measurements were from 0.01 to 0.72 V and from 45 to 1404 cells/mm3 X mm/s. Within these ranges, temporal variations induced by muscle contraction correlated well (overall r = 0.91), but the spatial variations associated with the resting state correlated poorly (overall r = 0.45). When the penetration of the laser light was limited to 0.3-0.4 mm (to make the volumes sampled by both techniques more comparable) the overall r of the spatial comparison increased to 0.86. It is concluded that the flowmeter (1) is affected by red cell perfusion below the tissue depth of 0.3-0.4 mm, and (2) can follow both the temporal and spatial variations of red cell perfusion in the tissue examined.