AJP - Heart and Circulatory Physiology, Vol 256, Issue 1 153-H161, Copyright © 1989 by American Physiological Society
Transfer function analysis of autonomic regulation. II. Respiratory sinus arrhythmia
J. P. Saul, R. D. Berger, M. H. Chen and R. J. Cohen
Division of Health Sciences and Technology, Harvard University-Massachusetts, Institute of Technology, Cambridge 02139.
An efficient new technique was developed to investigate heart rate control
at all physiologically relevant frequencies by using respiratory activity
as a frequency probe of the autonomic nervous response. The transfer
function from respiratory activity to heart rate was determined during
6-min periods in which the respiratory rate was voluntarily controlled in a
predetermined but erratic fashion. Changes in posture were used to
manipulate autonomic balance. Respiratory sinus arrhythmia was determined
to be a frequency-dependent phenomenon with the magnitude and phase
characteristics of a low-pass filter. In agreement with previous work, at
typical respiratory frequencies (greater than 0.15 Hz) increases in heart
rate occurred simultaneously with the onset of inspiratory activity;
however, at frequencies less than 0.15 Hz the phase relationship was quite
different, such that increases in heart rate preceded inspiration. Between
0.15 and 0.45 Hz, the transfer magnitude was consistently lower while the
subjects were in the upright posture than when in the supine posture, but
below 0.15 Hz, it was equal in both postures. A model for respiratory
modulation of heart rate, based on the atrial rate response characteristics
determined in the companion paper [Am. J. Physiol. 256 (Heart Circ.
Physiol. 25): H142-H152, 1989], suggests that the magnitude and phase
characteristics of the subjects in the supine and upright postures differ
because of relatively increased sympathetic outflow in the upright posture.
A precise and efficient characterization of respiratory sinus arrhythmia
can yield considerable insight into the autonomic regulation of the heart.
