Upper Airway Pressure-flow Relationships and Pharyngeal Constrictor EMG Activity During Prolonged Expiration in Awake Goats

We undertook the present investigation to establish whether narrowing/closure of the upper airway occurs during spontaneous and provoked respiratory rhythm disturbances and whether pharyngeal constrictor muscle recruitment occurs coincident with upper airway occlusion during prolonged expiratory periods. Upper airway pressure-flow relationships and middle pharyngeal constrictor (mPC) EMG activities were recorded in 11 adult female goats during spontaneous and provoked prolongations in expiratory time (Te). A total of 213 spontaneous prolongations of expiration were recorded. Additionally, 169 prolonged expiratory events preceded by an augmented breath were included in the analyses. In separate trials on different days, Te was prolonged by systemic administration of dopamine, by raising the inspired fraction of O(2) from 0.10 to 1.00 during poikilocapnic conditions or by systemic administration of clonidine. Continuous tonic activation of the mPC EMG was observed during each prolonged Te period regardless of the duration or initiating cause. However, significant increases in subglottic tracheal pressure, with expiratory airflow braking indicative of upper airway narrowing or closure, was only observed during spontaneous events without a preceding augmented breath and during clonidine-induced events. Tonic mPC activation proved an unreliable indicator of airway occlusion. Furthermore, mPC muscle activation alone is not sufficient to induce pharyngeal occlusion during prolonged expiration. Our data suggest that airway closure is not a common occurrence during provoked respiratory disturbances in awake goats. We propose that airway closure, when present during prolonged Te, is more likely dependent on activation of laryngeal adductor muscles with glottic braking independent of pharyngeal narrowing.