Vasodilation and muscle pump contribution to immediate exercise
hyperemia.
Tschakovsky, M. E., J. K. Shoemaker, and R. L. Hughson.
Department of Kinesiology, University of Waterloo, Waterloo,
Ontario, Canada, N2L 3G1
APStracts 3:0301H, 1996.
A rapid (within 0-5 seconds) increase in skeletal muscle blood flow
has been demonstrated following muscle contraction, yet the mechanism
remains unresolved. Recently, it was suggested that the entire rapid
exercise hyperemia could be attributed to the mechanical muscle pump
effect. Other evidence indicates that the muscle pump cannot increase
arterial flow. We measured human forearm blood flow with the arm
positioned above or below heart level during: 1) simulation of
rhythmic muscle pump function via repeated inflation/deflation of a
forearm cuff to 100 mmHg to achieve mechanical emptying of forearm
veins 2) 1 second single cuff inflations, 1 second voluntary forearm
contractions and 1 second contractions performed within a cuff
inflation. Rhythmic cuff inflation increased blood flow with the arm
below heart level (P<0.05) but not above. Flow following single
contractions was higher than flow following cuff inflation within 2
seconds (P<0.05). Peak flow increases due to a single mechanical
venous emptying (7.7 +/-0.7 ml/100ml/min) could account for 60% of
the peak flow increase due to muscle contraction (12.8 +/-1.0
ml/100ml/min) with the arm below heart level, while above heart level
mechanical venous emptying accounted for 46% of the flow increase due
to contraction (3.0 +/-0.4 ml/100ml/min vs. 6.5 +/-0.6 ml/100ml/min).
We conclude that a functional muscle pump does exist in the human
forearm in vivo, but that a rapid vasodilation detectable by 2
seconds also contributes to the early exercise hyperemia.
Received 7 May 1996; accepted in final form 24 June 1996.
APS Manuscript Number H407-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996