Respiratory-related heart rate variability persists during central
apnea in the dog: mechanisms and implications.
Horner, Richard L., Dina Brooks, Louise F. Kozar, Kezheng Gan, and
Eliot A. Phillipson.
Department of Medicine, University of Toronto, Toronto, M5S 1A8,
Canada
APStracts 2:0068A, 1995.
The aim of this study was to determine the mechanism(s) responsible
for the persistence of respiratory sinus arrythmia (RSA) during
central apnea. In five awake dogs, heart rate (hr) was recorded
during constant mechanical ventilation (MV) and during central apneas
produced by cessation of MV. For each of 10 control ventilator cycles
before cesation of MV, instantaneous HR was plotted against the time
from the onset of lung inflation; the fundamental and first harmonic
of a sine wave (at the ventilator frequency) was then fitted to the
HR data. For the control cycles, the mean r2 from the curve fits was
0.57 +0.07 showing that a significant component of the HR variability
was linked to the ventilator cycle. Following cessation of MV, RSA
persisted and only by the third `phantom' ventilator cycle during
apnea had the degree of fit consistently decreased compared to the
controls (p<0.02). The persistence of ventilator-linked RSA at the
onset of central apnea supports the concept of a `memory' in the
respiratory system. Toward the end of central apnea, HR variability
reappeared and had the periodicity and rhythmic profile of RSA on 81%
of occasions. The presence of RSA-like activity toward the end of
central apnea suggests that sub-threshold rhythmic respiratory
-related activity may be present even before the onset of detectable
lung volume changes.
Received 25 July 1994; accepted in final form 13 February 1995.
APS Manuscript Number A759-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 1 March 1995.