LARYNGEAL AND ABDOMINAL MUSCLE ELECTRICAL-ACTIVITY DURING PERIODIC BREATHING IN NONSEDATED LAMBS

We recently reported that glottic closure was present throughout centr al apneas in awake lambs. The present study tested whether glottic clo sure was also observed during periodic breathing (PB). We attempted to induce PB in 21 nonsedated lambs on return from hypocapnic hypoxia to room air. Airflow and thyroarytenoid (a laryngeal constrictor, n = 16 ), cricothyroid (a laryngeal dilator, n = 10), and abdominal (n = 9) m uscle electrical activity (EMG) were monitored continuously. PB was ob served in 16 lambs, with apneic phases in 8 lambs. Thyroarytenoid musc le EMG was observed at the nadir of PB, either throughout apnea or wit h prolonged expiration during the lowest respiratory efforts. Phasic i nspiratory cricothyroid muscle EMG and phasic expiratory abdominal EMG disappeared at the nadir of PB. Active glottic closure at the nadir o f PB, without abdominal muscle contraction, could be a beneficial mech anism, preserving alveolar gas stores for continuing gas exchange duri ng the apneic/hypopneic phase of PB. However, consequences of active g lottic closure on ventilatory instability, either enhancing or reducin g, are unknown.