Time-dependent responses of expiration reflex in cats

We investigated the effectiveness of the "expiration reflex" in 10 anesthetized spontaneously breathing cats. The expiration reflex was produced by mechanical stimulation of the vocal folds and electrical stimulation of the superior laryngeal nerve at different moments in the respiratory cycle and at various levels of respiratory chemical drive. The effectiveness of the expiration reflex was evaluated from sudden changes in expiratory flow immediately following the stimulation. Both mechanical and electrical stimulations given during early inspiration caused little or no expiratory efforts, whereas stimulations given during early expiration or hypocapnic apnea produced a typical expiration reflex. Changes in arterial CO2 and O2 partial pressures influenced neither the relationships between the stimulation and its effect on the expiration reflex nor the strength of the expiration reflex. These results indicate that the timing of stimulation with relation to the phase of the respiratory cycle is critical to its effect on the expiration reflex and that changes in respiratory chemical drive do not modify the expiration reflex characteristics.