Reaction in man of resistance and capacity vessels in forearm and hand to leg exercise.

Abstract

The reaction of resistance and capacity vessels in forearm and hand to leg exercise was studied in normal subjects. Following a transient increase in forearm blood flow (strain-gauge plethysmograph) and decrease in arterial blood pressure with onset of exercise, the flow remains at the pre-exercise value or, with severe exercise (1,200 kg-m/min), decreases to less than half that value as arterial pressure increases. These changes in forearm flow resulted from dilatation followed by constriction of muscle vessels, and with moderate to severe exercise a gradual dilatation of vessels in forearm skin as deduced from changes in O2 saturation of blood from forearm muscle and skin veins. The resistance vessels in the hand constricted with onset of exercise and dilated again toward the end of the exercise period. The capacity vessels constricted with onset of exercise; the constriction persisted throughout exercise and was graded like that of the resistance vessels in muscle to the work load. These vessel reactions were mediated by sympathetic fibers and could be blocked in the forearm by local heating. The venomotor reflex might be elicited by the muscle contractions.