EFFECT OF DIGITAL NERVE BLOCKADE ON HEAT-INDUCED VASOCONSTRICTION IN THE HUMAN FINGER

The present study was performed to investigate the mechanism of heat-i nduced vasoconstriction (HIVC) in human fingers. The left fingers of f ive male subjects were immersed in water controlled at an initial temp erature of 35.0 degrees C. The blood flows (BF) of the left index and fourth fingers were measured continuously with laser-Doppler flowmeter probes, and the temperatures of the middle finger and water bath were also monitored continuously using thermistor probes. Arterial blood p ressure and heart rate were measured every minute before and during lo cal finger warming. A local anesthetic (0.5% bupivacaine hydrochloride ) or saline at a volume of 5.0-8.0 mi was aseptically injected into th e base of the fourth or index finger, respectively. After finger BFs h ad been stabilized for greater than or equal to 10 min, the fingers we re warmed by raising the water bath temperature from 35.0 to 41.5 degr ees C in 14 min. The BF of the index finger fell significantly for 6 m in after local warming was commenced (at water bath temperatures betwe en 35.5 and 37.5 degrees C) without associated changes in mean arteria l blood pressure, indicating the occurrence of HIVC. Then BF increased toward prewarming levels. The local anesthetic injection, however, co mpletely abolished HIVC in the fourth finger. These results suggest th at, in humans, innervation to finger vessels is indispensable for prod ucing HTVC and hence that a local mechanism, such as myogenic vascular response to high temperature, may not be involved in the induction of HIVC.