AJP - Regulatory, Integrative and Comparative Physiology, Vol 237, Issue 5 260-R265, Copyright © 1979 by American Physiological Society
Effect of timing of FICO2 changes on ventilatory period in domestic fowl
R. D. Tallman Jr, A. L. Kunz and D. A. Miller
These experiments were conducted to see if the pacing phenomenon found by
Kunz and Miller (Respir. Physiol., 22: 167--177, 1974) in the open-loop,
unidirectionally ventilated chicken is important in normally breathing
birds. In this study, chickens breathed spontaneously through a
tracheostomy from a gas source in which the fraction of CO2 (FICO2) could
be rapidly changed. A feedback algorithm kept the FICO2 at 0.05 except for
a constant duration pulse (approx 0.6 s) of low FICO2 given tau seconds
after the beginning of each inspiration. In all birds tested an increase in
tau resulted in a proportional increase of both inspiratory period (TI),
expiratory period (TE), and the total period (Ttot). Increases in TI were
from 0.5 to 1.0 times the increase in tau. Dynamic expeiments showed TI
usually changed on the next breath after a step change in tau, and
sinusoidal modulation of tau caused concurrent sinusoidal changes in TI,
TE, and Ttot. These findings indicate that the phenomenon that produced
pacing in the unidirectionally ventilated birds is important to the
ventilatory pattern of normal breathing.
