Is respiratory sinus arrhythmia a good index of cardiac vagal tone
in exercise?.
Casadei, Barbara, James Moon, Jim Johnston, Alberto Caiazza, and Peter
Sleight.
Department of Cardiovascular Medicine, John Radcliffe Hospital,
Oxford OX3 9DU, United Kingdom
APStracts 3:0201A, 1996.
To assess the relative roles of neural and non-neural mechanisms in
respiratory sinus arrhythmia (RSA) at rest and during exercise
(steady-state supine cycle-ergometry at 25% of peak VO2), we studied
10 healthy males (mean age 21+/-1 years) before (control) and during
ganglion blockade (GB) with trimetaphan camsylate (3 to 5 mg.min-1,
i.v.). GB was confirmed by the abolition of the reflex bradycardia in
response to i.v. phenylephrine, and of the blood pressure rise with
cold pressor test. RSA was calculated from the power of the spectral
component of the R-R interval variability centered at the breathing
frequency. GB decreased but did not abolish RSA. At rest, this non
-neural component of RSA was negligible, accounting for less than 1%
of the control RSA. During GB, exercise did not affect RSA
significantly. However, since control RSA was decreased by exercise,
the proportion of non-neural RSA increased by 32% (range from 17 to
75%). These results indicate that as the vagal tone decreases with
exercise, an increasing proportion of RSA is due to non-neural
mechanisms.
Received 5 May 1995; accepted in final form 27 February 1996.
APS Manuscript Number A479-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 23 April 96