In resting, awake cats, we measured tidal volume, inspiratory and expiratory times, upper airway resistance, belly pressure, and diaphragmatic electromyograms. Expiratory duration (spontaneous te) during air breathing surpassed the amount of time needed for the intubated respiratory system to passively collapse (passive te). The post-inspiratory activity of the diaphragm and the resistance of the upper airway both influence expiratory flow and contributed to the difference between spontaneous and passive values.
A decrease in upper airway resistance, a rise in abdominal expiratory muscle activity, and, in some animals, a decrease in the diaphragm’s post-inspiratory activity were all consistently brought on by hypercapnia.
The general increase in cats tested 1-4 weeks after bilateral cervical vagotomy is consistent with the functioning of a volume-related feedback system controlling the in the intact animal.
Our investigation of the variables affecting expiratory flow reveals the significance of fluctuations in upper airway resistance caused by vocal cord motions. We suggest that the larynx significantly influences both the respiratory frequency and the action of volume-related feedback.
