Journal of Applied Physiology, Vol 65, Issue 2 563-569, Copyright © 1988 by American Physiological Society
Influence of phasic afferent information on phrenic neural output during hypercapnia
A. S. Menon, S. J. England, E. Vallieres, A. S. Rebuck and A. S. Slutsky
Department of Medicine, Mount Sinai Hospital, Toronto, Ontario, Canada.
We measured the moving time average (MTA) of the phrenic neurogram before
and after removal of phasic afferent information from the lungs, chest
wall, and oscillations in blood gases by using constant-flow ventilation
(CFV). Anesthetized dogs were studied at various levels of steady-state and
progressive hypercapnia during spontaneous breathing and during CFV. When
steady-state and progressive hypercapnia were compared, the frequency and
height of the MTA phrenic neurogram were independent of the rate of
induction of hypercapnia during each mode of ventilation. During
spontaneous ventilation, the response to hypercapnia comprised mainly an
increase in frequency with only a slight increase in the amplitude of the
MTA phrenic waveform. During muscular paralysis and CFV, the responses were
similar to those observed after vagotomy with mainly an increase in the
amplitude and only a small increase in frequency. For both spontaneous
breathing and CFV, increases in frequency were achieved mainly by a
shortening in expiratory time with the inspiratory time remaining
relatively constant. Our data support the concept of a centrally patterned
respiratory generator, whose inherent pattern is modified by phasic
feedback from peripheral receptors mainly of vagal origin.
