Journal of Applied Physiology, Vol 47, Issue 1 233-239, Copyright © 1979 by American Physiological Society
Initiation of each avian inspiration by a CO2 threshold mechanism
D. A. Miller and A. L. Kunz
The avian respiratory oscillator has been investigated in a
unidirectionally ventilated chicken by changing the dynamic pattern of
inflow CO2 concentration (FCO2). Stimulation with periodic FCO2 results in
a one-to-one synchronization of the respiratory movements that we have
called pacing (Respir. Physiol. 22: 167--177, 1974). A two-parameter CO2
threshold model is proposed to explain this behavior. The model states that
when FCO2 reaches a threshold level (L), it initiates the beginning of
inspiration a constant time interval (LB) later. According to this model,
when a triangular FCO2 concentration is used to synchronize the breathing
pattern, the time from the minimum of the wave form to the beginning of
inspiration (C-B interval) is dependent on the mean value and the rate of
rise of FCO2 as determined by period and amplitude of the triangle.
Particularly interesting is the prediction that the direction of the
relationship (increasing or decreasing) between FCO2 amplitude and the C-B
interval is dependent on whether the mean value of FCO2 is above or below
the threshold level. Experimental data obtained during amplitude changes
support the above prediction.
