Decrease in lung volume-related feedback enhances laryngeal reflexes to negative pressure.

Negative pressure applied to the upper airway has an excitatory effect on the activity of upper airway muscles and an inhibitory effect on thoracic inspiratory muscles. The role of lung volume feedback in this response was investigated in 10 anesthetized spontaneously breathing adult rabbits. To alter lung volume feedback, the lower airway was exposed to SO2 (250 ppm for 15 min), thereby blocking slowly adapting receptors (SARs). Negative pressure pulses (5, 10, and 20 cmH2O, 300-ms duration) were applied to the functionally isolated upper airway before and after SAR blockade. Tracheal airflow and electromyogram (EMG) of the genioglossus and alae nasi were recorded. Peak EMG, peak inspiratory flow, tidal volume, and respiratory timing of control breaths (3 breaths immediately preceding test) and test breaths were determined. Analysis of variance was used to determine the significance of the effects. Negative pressure pulses increased peak EMG of genioglossus and alae nasi and inspiratory duration and decreased peak inspiratory flow. These effects were larger after SAR blockade. We conclude that a decrease in volume feedback from the lung augments the response to upper airway pressure change.