Prolonged active glottic closure after barbiturate-induced respiratory arrest in lambs.

We recently showed that the glottis is actively closed throughout post-hyperventilation, hypocapnic central apnea in lambs. The present study was designed to test whether the glottis is also closed in non-hypocapnic central apnea. Twenty-seven lambs aged 2 to 30 days were intravenously injected with 325 mg of sodium pentobarbital, so as to obtain breathing arrest. Airflow was recorded via a facial mask and pneumotachograph, along with the electromyographic activity (EMG) of the thyroarytenoid muscle (TA, a glottic adductor). With the onset of apnea, continuous TA EMG appeared in a few seconds and rose rapidly. Brief inspiratory gasps were observed in eight lambs, and TA EMG was abruptly inhibited for the exact duration of the gasps. The continuous TA EMG then disappeared after 115 to 230 sec. We conclude that the glottis is actively closed during fatal non-hypocapnic central apnea in lambs. Our data suggest that active glottic closure occurs with major depression of central inspiratory drive.