Contribution of arteriovenous anastomoses to vasoconstriction induced by local heating of the human finger.

Blood flows in the finger were measured simultaneously by laser Doppler flowmetry and by venous occlusion plethysmography in a warm environment (35 degrees C, 40% RH). One hand was immersed in a water bath the temperature of which (Tw) was raised every 10 min by steps of 2 degrees C from 35 to 43 degrees C, while the other hand was kept immersed in water at 35 degrees C. Finger blood flow in the heated hand (BFw) measured with venous occlusion plethysmography was significantly lower than that in the control hand (BFc) at Tw of 39-41 degrees C. At Tw of 43 degrees C, however, the finger BFw returned to the level of BFc after a transient decrease. In contrast, blood flow in the heated hand measured with laser Doppler flowmetry (LDFw) increased steadily as the Tw was raised from 37 to 43 degrees C, while that in the opposite hand (LDFc) remained unchanged. Assuming that the laser Doppler flowmetry does not measure blood flow through AVAs located deeply in the skin of the finger but measures flow through the superficial capillaries, the results suggest that the decrease in finger blood flow in response to local heating may be limited to AVAs, and superficial vessels may not contribute to this heat-induced vasoconstriction of the finger.