Journal of Applied Physiology, Vol 73, Issue 3 1052-1057, Copyright © 1992 by American Physiological Society
Entrainment of respiratory rhythm to respiratory oscillations of arterial PCO2 in vagotomized dogs
E. Takahashi, K. Tejima and K. Yamakoshi
Division of Biomedical Systems Engineering, Faculty of Engineering, Hokkaido University, Sapporo, Japan.
The aim of this study was to demonstrate that the medullary respiratory
rhythm generator is capable of entraining to respiratory oscillations of
arterial PCO2 (CO2 oscillations). We used 10 anesthetized, paralyzed,
vagotomized, and mechanically ventilated dogs. First, rate of mechanical
ventilation was manually adjusted so that it matched the dog's spontaneous
respiratory rate, which established a constant phase relationship between
the mechanical ventilation and the burst of phrenic neurogram (initial
phase). Then this phase relationship was temporally disturbed by a brief
electrical stimulation of the superior laryngeal nerve (SLN). In the
control group, the initial phase and the steady-state phase relationship
after SLN stimulation were randomly distributed within the phase plane,
implying no interaction between the respiratory center and mechanical
ventilation. In contrast, when CO2 output from the lung was increased
2.6-fold above the control level by venous CO2 loading, the initial phase
and the steady-state phase after SLN stimulation were locked in such a way
that the onset of the burst of phrenic neurogram coincided with the peak of
CO2 oscillations. This was not demonstrated when the dog was made
hyperoxic. We therefore conclude that the respiratory center could entrain
to phasic chemical afferent inputs originating from CO2 oscillations,
provided they are considerably amplified.
