Ventilatory phase duration in the chicken: role of mechanical and CO2 feedback

Abstract

Awake upright White Leghorn roosters (Gallus domesticus) were unidirectionally ventilated. Electromyographic activity from inspiratory and expiratory muscles was recorded to demarcate inspiration and expiration. During inspiration, the rate of inflation of the air sac system was varied while the CO2 concentration of the gas passing through the lungs was maintained constant. Inspiratory duration was inversely related to the rate of inflation, producing an inspiratory volume-time threshold (VT) curve with a negative slope. When the CO2 concentration was increased in the lungs, the inspiratory VT curve shifted to the right with a concurrent increase in slope. If the rate of deflation was varied during expiration, it was found that expiratory duration was inversely related to the rate of deflation, producing an expiratory VT curve with a positive slope. Increasing the CO2 concentration shifted the curve to the left with an increased slope. These results indicate that inspiratory and expiratory phase durations are a function of both mechanical and chemical feedback.

Singing with reduced air sac volume causes uniform decrease in airflow and sound amplitude in the zebra finch

“…These mechanoreceptors are most likely located in the air sac system (Kubke et al, 2004) and probably respond to volume changes, particularly during the inspiratory phase (Ballam et al, 1982;Molony, 1974). In cardinals, an increase in air sac volume by injection of small air pulses into the anterior thoracic air sac during song resulted in decreased EMG activity in the abdominal expiratory muscles (Suthers et al, 2002).…”

“…In our experiment, the injected air sacs were permanently full and therefore volume changes did not occur in these air sacs. Because volume change is the most likely physical variable to alter the firing rate of these receptors (Ballam et al, 1982;Molony, 1974), feedback information may not have been available to correct for our manipulation.…”

Vagal innervation of the air sacs in a songbird, Taenopygia guttata

“…1978). Some of the innervation seems likely to be supplied by the vagus nerve, because changes in the volume of the air sacs, without a change in , have been shown to affect ventilatory timing, and this effect is dependent on an intact vagus (Ballam et al. 1982, 1985; Gleeson & Molony, 1989).…”