Coordination of swallowing and phases of respiration during added respiratory loads in awake subjects.

In order to test the hypothesis that different types of respiratory mechanical loads may differently modify the coordination of respiration and swallowing, we investigated the coordination of respiration and swallowing during resistive and elastic loads in 14 healthy subjects. Ventilation was monitored with a pneumotachograph and reflex swallowing was elicited by continuous infusion of distilled water into the pharynx (3 ml/min) and recorded on a submental electromyogram while the subject breathed through a device with a flow-resistive load (180 cm H2O/L/s), an elastic load (70 cm H2O/L), or without any external load. We found that addition of a flow-resistive load did not influence the frequency of swallowing, whereas addition of an elastic load caused a significant increase in swallowing frequency during continuous infusion of water. Analysis of the timing of swallowing in relation to respiratory cycle phase revealed that with flow-resistive loading, swallows occurred preferentially during the inspiratory-expiratory (I-E) transition, whereas with elastic loading, swallows occurred preferentially during the expiratory-inspiratory (E-I) transition. Signs of laryngeal irritation were observed most often during the elastic loading following E-I swallows. These results indicate that different types of respiratory mechanical loads can differently modify this coordination of respiration and swallowing, and suggest that the coordination may be compromised more with elastic loading than with flow-resistive loading.