AJP - Heart and Circulatory Physiology, Vol 256, Issue 1 142-H152, Copyright © 1989 by American Physiological Society
Transfer function analysis of autonomic regulation. I. Canine atrial rate response
R. D. Berger, J. P. Saul and R. J. Cohen
Division of Health Sciences and Technology, Harvard University-Massachusetts Institute of Technology, Cambridge 02139.
We present a useful technique for analyzing the various functional
components that comprise the cardiovascular control network. Our approach
entails the imposition of a signal with broad frequency content as an input
excitation and the computation of a system transfer function using spectral
estimation techniques. In this paper, we outline the analytical methods
involved and demonstrate the utility of our approach in studying the
dynamic behavior of the canine cardiac pacemaker. In particular, we applied
frequency-modulated pulse trains to either the right vagus or the cardiac
sympathetic nerve and computed transfer functions between nerve stimulation
rate and the resulting atrial rate. We found that the sinoatrial node (and
associated automatic tissue) responds as a low-pass filter to fluctuations
in either sympathetic or parasympathetic tone. For sympathetic
fluctuations, however, the filter has a much lower corner frequency than
for vagal fluctuations and is coupled with a roughly 1.7-s pure delay. We
further found that the filter characteristics, including the location of
the corner frequency and rate of roll-off, depend significantly on the mean
level of sympathetic or vagal tone imposed.
