Latency of muscle chemoreflex to vascular occlusion of active
muscle during dynamic exercise.
Sheriff, Don D.
Division of Cardiovascular Research, St. Elizabeth's Medical
Center, Boston, Massachusetts 02135
APStracts 3:0475H, 1996.
When oxygen delivery to active muscle is too low for the ongoing rate
of metabolism, metabolites accumulate and activate a muscle
chemoreflex that raises arterial pressure. During static muscular
contractions, the latency to the onset of increments in sympathetic
activity attributed to the muscle chemoreflex is long (1-2 min). This
long latency might be due to slow accumulation of metabolites
attributable to low rates of metabolism. Since shortening
contractions at a given force per unit time have a much higher energy
cost than do static contractions, the muscle chemoreflex should have
a much shorter latency during dynamic exercise than during static
contractions, and the latency should shorten further with rising
exercise intensity. To test these ideas, the latency to the onset of
the rise in arterial pressure induced by the muscle chemoreflex
following vascular occlusion of active muscle was measured in 4 dogs
exercising on a treadmill. During steady-state exercise of mild to
moderate intensity, pressor responses to muscle ischemia were
elicited by rapid, complete occlusion of the terminal aorta; this
procedure mimics the blockage of muscle blood flow that occurs
normally during static contractions. There was a statistically
significant effect of exercise intensity on latency (p <0.001).
The latency was 23.5 +/-4.5, 16.4 +/-5.6, and 10.1 +/-2.3 seconds
(mean +/-SE) at 3.2 km/h 0% grade, 6.5 km/h 0% grade, and 6.5 km/h
10% grade, respectively. Also, the rate of rise of arterial pressure
during chemoreflex activation increased progressively with rising
exercise intensity from 0.8 +/-0.2 mmHg/s during exercise at 3.2 km/h
0% grade to 2.0 +/-0.5 mmHg/s during exercise at 6.5 km/h 10% grade.
Thus the latency of the muscle chemoreflex in response to vascular
occlusion during mild dynamic exercise is shorter than has been
reported during static contractions of moderate intensity.
Received 27 November 1995; accepted in final form 18 October
1996.
APS Manuscript Number H1100-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996