Synchronous assessment of human skin microcirculation by laser Doppler flowmetry and dynamic capillaroscopy

Synchronous assessments of microcirculatory flow in human skin have been made by the techniques of laser Doppler flowmetry and dynamic capillaroscopy in adjacent areas of the same nailfold. Microvascular flow was studied at rest, following release of arterial occlusion and during application of venous occlusion in seven normal subjects. Despite broad comparability in the pattern of responses recorded by the two techniques certain significant differences were observed. Vasomotor activity of a similar frequency (4 to 9 cycles per min) was recorded by both techniques, but the activity was asynchronous. The amplitude of the cyclical change in the mean resting flow value recorded by dynamic capillaroscopy was considerably greater than that recorded by laser Doppler (X +/- SD, 25.3 +/- 7.0% mean rest flow; 11.4 +/- 4.9% mean rest flow, p less than 0.01). The time to peak flow following release of a 60 s arterial occlusion was significantly longer as assessed by dynamic capillaroscopy (5.7 +/- 1.6 s: 3.3 +/- 1.0 s. p less than 0.02). In response to a venous congestion pressure of 50 mm Hg, capillary flow rate fell to 24 +/- 6% of the resting flow value as assessed by dynamic capillaroscopy over the first 30 s of occlusion. Laser Doppler flowmetry also recorded a fall in microcirculatory flow to 59 +/- 21% of resting flow value during this period, but this reduction was significantly less than that recorded by dynamic capillaroscopy (p less than 0.05). These discrepancies are interpreted as evidence that laser Doppler flowmetry records blood flow in vessels in addition to the superficial, nutritional capillaries.