Phasic vagal influence on the rate and timing of reflex swallowing

We investigated the effects of sudden changes in ventilation induced by voluntary hyperpnea and breath-holding on repetitive reflex swallowing elicited by continuous infusion of distilled water into the pharynx in 13 healthy subjects. Ventilation was monitored using a pneumotachograph, and swallowing was identified by submental electromyography with interruption of airflow. We found that voluntary hyperpnea decreased the swallowing frequency whether end-tidal CO(2) tension was maintained at normocapnia or allowed to be hypocapnic. Also, the frequency of swallowing immediately increased with the start of breath-holding, but there was a sudden decrease in swallowing frequency during the hyperpnea observed immediately after the resumption of ventilation (post-breath-holding hyperpnea). The preponderant coupling of swallows with the expiratory phase was lost during voluntary hyperpnea but was maintained during post-breath-holding hyperpnea. These observations may suggest that vagally mediated reflexes are operative in normal physiologic situations and play an important role in the control of swallowing rate as well as in the timing of swallowing in reference to the respiratory cycle.