AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 1 55-R62, Copyright © 1987 by American Physiological Society
Phase resetting and dysrhythmic responses of the respiratory oscillator
D. Paydarfar and F. L. Eldridge
This study explores resetting of respiratory rhythm by facilitatory
perturbations. The midbrain reticular formation and periaqueductal gray
matter were electrically stimulated to evoke facilitation of phrenic nerve
activity in nine anesthetized, vagotomized, and glomectomized adult cats.
The animals were paralyzed and servo-ventilated to keep end-tidal PCO2
constant. Brief midbrain stimuli were given at various times in the
respiratory cycle and the times of onset of rescheduled breaths after
stimulation were measured. A plot of phase resetting as a function of
stimulus strength and time of delivery defined a helicoid surface. The axis
of this helicoid identified a unique stimulus which, when given at the
inspiratory-expiratory transition, resulted in unpredictable resetting of
respiratory rhythm. This stimulus had a strength that was intermediate to
that which identified types 1 and 0 resetting. In one experiment, the
singular stimulus often initiated a breath having prolonged inspiratory
activity; resumption of the normal rhythm was delayed significantly (P less
than 0.01). We conclude that the dysrhythmias observed in this study
represent the respiratory oscillator's phase singularity.
