Slowing of the carotid-cardiac baroreflex with standing and with
isometric and dynamic muscle activity.
Sundblad, Patrik, and Dag Linnarsson.
Environmental Physiology Laboratory, Department of Physiology and
Pharmacology, Karolinska Institutet, S-171 77 Stockholm, Sweden
APStracts 3:0133H, 1996.
We hypothesized that the carotid-cardiac baroreflex becomes slowed in
conditions with increased sympathetic activity. Changes in heart rate
(HR) and blood pressure in response to 10 sec trains of 50 mm Hg
pulses of neck suction (NS) were studied in six male subjects during
supine rest, upright rest, isometric arm exercise at 30% of maximum
voluntary contraction and dynamic leg exercise at 100 W in the
sitting position. Estimated mean carotid distending pressure
increased by about 20 mm Hg with 50 mm Hg QRS-triggered pulsatile NS.
Repeated NS sequences were performed in each condition. The amplitude
of the bradycardic response was highly variable among the subjects
and did not differ significantly between conditions, mean values
ranging 0.3 - 0.6 beats x min-1 mm Hg-1. In supine rest, the full
bradycardic response appeared within less than 1 second, i.e. during
or immediately after the R-R-interval of the first NS pulse. In the
other conditions it took significantly longer, 2-3 seconds or 3-7 R
-R-intervals, for the full HR responses to develop. Our results
support the notion that the carotid-cardiac baroreflex in man becomes
slowed under conditions of concurrent sympathetic stimulation.
Received 8 May 1995; accepted in final form 26 March 1996.
APS Manuscript Number H432-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 April 96