Modulation of swallowing reflex by lung volume changes.

We investigated the effects of changes in lung volume on coordination of respiration and swallowing in 11 healthy subjects. Swallowing reflexes were elicited by bolus injections of a small amount of distilled water (1 ml) and by continuous infusion of distilled water (3 ml/min) into the pharynx at three different levels of lung volume. The lung volume was changed by application of negative extrathoracic pressure (0, -20, and -40 cm H(2)O). We found that increases in lung volume prolonged the latency of swallows elicited by bolus injection of water and decreased the number of swallows during continuous infusion of water. In addition, the preponderant coupling of swallows with the expiratory phase observed before application of negative extrathoracic pressure was lost during application of negative extrathoracic pressure. These results may indicate that lung inflation has an inhibitory influence on the swallowing reflex, and modulates the timing of swallowing in reference to the respiratory cycle.