Cutaneous blood flow rates during orthostatic manoeuvres measured by laser Doppler flowmetry

The validity of Laser Doppler Flowmetry for measurements of changes in skin blood flow rates during orthostatic manoeuvres was evaluated. Fifteen healthy subjects were investigated. Relative skin blood flow rates on the dorsum of the hand were measured during stepwise raising and lowering of the arm in 10 cm increments to an extreme position of 40 cm below respectively above heart level. All measurements at test levels were preceded and followed by measurements at reference level, i.e. heart level. At all levels of arm elevation, relative blood flow rates were significantly increased compared with the corresponding reference level (p = 0.0005). This was unexpected in view of the auto-regulatory mechanism. Highly significant blood flow rate reductions were found at all levels of arm lowering. This is in contrast to previous findings of unchanged skin blood flow rate to a point of approximately 35 cm below heart level, where the veno-arteriolar reflex is elicited.