Transfer function analysis of vagal control of heart rate during synchronized vagal stimulation. Mokrane, A., Leblanc A. R., Nadeau R. Institut de g[acute]enie biom[acute]edical, Ecole Polytechnique / Faculty of medicine, Universit[acute]e de Montr[acute]eal and Research Center, H[circumflex]opital du Sacr[acute]e-Coeur de Montr[acute]eal
APStracts 2:0258H, 1995.
Synchronized electrical stimulation was used to study the heart rate (HR) response to fluctuations in parasympathetic input to the sinus node in anesthetized dogs. This was obtained by varying the time interval (interpulse interval) between stimulatory vagal pulses. Spectral methods were used to estimate transfer functions between the excitatory signal and the resulting HR response for different intensities of vagal stimulation. The intensity of vagal stimulation was proportional to the number of pulses delivered in each cardiac cycle. From the estimated transfer functions and based on a mathematical model of the time course of acetylcholine (ACh) concentration at the sinus node, filter models were derived by using a system identification approach. HR response was characterized by a combination of two different filter behaviors: a low-pass filter behavior of mean cut-off frequency of 0.065 Hz and an all-pass filter behavior. The magnitude of the low-pass filter gain decreased with increasing intensity of vagal stimulation. The magnitude of the all -pass filter gain increased then decreased with increasing intensity of vagal stimulation. The all-pass filter characteristics of HR response during synchronized stimulation of the vagus nerves are specific to this mode of stimulation since they were not observed in nonsynchronized modes of vagal stimulation. We can conclude that during synchronized vagal stimulation, the HR response exhibits both a slow dynamic component and a fast component related to beat-to-beat variations. 

Received 14 November 1994; accepted in final form 12 June 1995.
APS Manuscript Number H1014-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  6 July 1995.