Laryngeal and abdominal muscle electrical activity during periodic breathing in nonsedated lambs.

We recently reported that glottic closure was present throughout central apneas in awake lambs. The present study tested whether glottic closure 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) muscle electrical activity (EMG) were monitored continuously. PB was observed in 16 lambs, with apneic phases in 8 lambs. Thyroarytenoid muscle EMG was observed at the nadir of PB, either throughout apnea or with prolonged expiration during the lowest respiratory efforts. Phasic inspiratory cricothyroid muscle EMG and phasic expiratory abdominal EMG disappeared at the nadir of PB. Active glottic closure at the nadir of PB, without abdominal muscle contraction, could be a beneficial mechanism, preserving alveolar gas stores for continuing gas exchange during the apneic/hypopneic phase of PB. However, consequences of active glottic closure on ventilatory instability, either enhancing or reducing, are unknown.