Muscle chemoreflex alters carotid sinus baroreflex response in
humans.
Papelier, Y., P. Escourrou, F. Helloco, L. B. Rowell.
Laboratoire S.T.A.P.S. de l'Universit[theta] Paris-Sud, b[GAMMA]t.
335, 91405 Orsay-cedex, France, Laboratoire de Physiologie,
Facult[theta] de M[theta]decine, 94276 Kremlin Bictre France,
Department of Physiology and Biophysics - University of Washington
School of Medicine, SJ 40, Seattle, WA 98195, USA. Tel: (33) 1 69 41
62 87 - Fax: (33) 1 69 41 62 37
APStracts 3:0477A, 1996.
The arterial baroreflex opposes pressor responses to muscle ischemia
(muscle chemoreflex). Our experiments sought to quantify the unknown
effects of muscle chemoreflex on carotid sinus baroreflex (CSB)
sensitivity. We generated CSB stimulus-response curves by pulsatile
application (triggered by each ECG R-wave) of positive and negative
neck pressure (from plus 60 to minus 80 mm Hg in 20 mm Hg steps of 20
seconds each) in 7 normal young men. Stimulus-response curves were
obtained at rest (upright), during the last 3 minutes of upright
cycle ergometer exercise (150 watts), and at the first minute of
post-exercise recovery with leg circulation free (control). A second
study repeated the same procedures except that leg circulation was
occluded 20 seconds before end of exercise to elicit muscle
chemoreflex, and occlusion maintained during recovery measurements
(about 3-4 min. duration). Stimulus-response curves for CSB were
shifted upward and rightward (25 mm Hg) to higher arterial pressure
(BP) by exercise, and less so (10 mm Hg) in recovery (free leg flow).
Post-exercise occlusion (muscle chemoreflex) raised BP and shifted
stimulus-response curves above exercise curves : CSB gain rose from -
0.26 0.06 (control) to - 0.44 0.08 (occlusion) during positive neck
pressure application and was reduced from - 0.14 0.04 to zero (- 0.04
0.03) during negative neck pressure. Heart rate responses during
post-exercise muscle chemoreflex were not significantly different
from control. Results reveal a non-linear summation of CSB and muscle
chemoreflex effects on BP. BP raising capability of muscle
chemoreflex enhances CSB responses to hypotension but overpowers
baroreflex opposition to hypertension.
Received 17 July 1995; accepted in final form 21 October 1996.
APS Manuscript Number A773-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996