Influence of apnea on cardiovascular responses to neck suction
during exercise.
Sundblad, Patrik, and Dag Linnarsson.
Environmental Physiology Laboratory, Department of Physiology and
Pharmacology, Karolinska Institutet, S-171 77 Stockholm
APStracts 3:0141H, 1996.
Short lasting neck suction (NS) is a common method to assess the
carotid-cardiac baroreflex, and NS is usually applied during apnea in
order to avoid breath-synchronous variations of heart rate and blood
pressure. We hypothesized that the apnea might provoke cardiovascular
effects which could confound the heart rate and blood pressure
responses to NS. Heart rate and blood pressure responses to 10 sec
trains of 50 mmHg pulses of NS were studied in six male subjects
during supine rest, upright rest, isometric arm exercise at 30 % of
maximal voluntary contraction and dynamic leg exercise at 100 W in
the sitting position. Repeated NS sequences were performed during
apnea preceded by a relaxed expiration to functional residual
capacity and during eupnea. The initial heart rate responses to NS
were similar during eupnea and apnea in all conditions. However,
during isometric and dynamic exercise, recordings made under eupneic
and apneic conditions differed during the second half of the NS
period. During apneic isometric arm contraction, the elevation of
mean carotid distending pressure (MCDP) (arterial pressure at carotid
level minus NS pressure) was maintained at a 25-35 per cent higher
level than during eupneic isometric exercise over the last half of
the NS period. In dynamic exercise, mean arterial pressure and MCDP
started to increase after 3-5 seconds of apneic NS, whereas they were
maintained during eupnea. One to three seconds later, HR started to
drop markedly in apneic subjects, to reach values 20 beats x min-1
lower than those in eupneic subjects at the end of the NS. We
conclude that cardiovascular effects of apnea may appear after only 8
sec of apnea in dynamic exercise and therefore could confound
responses to NS.
Received 8 December 1995; accepted in final form 26 March 1996.
APS Manuscript Number H1144-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96