A study of cutaneous reactive hyperaemia by laser-Doppler flowmeter

Finger nailfold skin blood flow was monitored by laser-Doppler flowmeter in 18
 healthy volunteers after the occlusion of digital
arteries. The primary aim of the study was to characterize the microcirculatory pattern of 
postocclusive reactive hyperaemia. Laser-Doppler flowmetry revealed two parts of the hyperaemic response. The first part was characterized by maximum laser-Doppler flow and
 large amplitude of the oscillations which correspond to heart beats. The second part was 
characterized by the appearance of periodic 
oscillation with fundamental frequency from
 0.07 to 0.19 Hz. In order to elucidate the physiological background of this phenomenon, the 
cutaneous vascular bed was exposed to the changes of transmural pressure, secured by different position of the limb, and to different levels of ischaemia, accomplished by varying the duration of occlusion. It was found that the
 area under the first part of laser-Doppler flow increased with prolongation of arterial occlusion. The increment was found to be significant between 1 and 4 (p=0.009) and 4 and 8
 (p=0.006) minutes of occlusion. Also, the area
 proved to be independent of transmural pressure (R=0.06, p=0.74). In contrast, the fundamental frequency of periodic oscillations in the
 second part of the response proved to be pressure dependent but showed no significant correlation with the duration of arterial occlusion 
(p<0.001). It is our conclusion that the first part
 of laser-Doppler hyperaemic response reflects
 predominant contribution of metabolic components in contrast to the periodic oscillations in
 the second part of the response, which very likely reflect myogenic response.