Laryngeal response to hypoxia in awake lambs during the first postnatal days.

We recently showed that hypoxia does not induce active expiratory glottic adduction in awake lambs more than 10 d old. To reconcile our results with previous data from other researchers, we hypothesized that an active expiratory glottic closure might still be part of the response to hypoxia in the very first postnatal days. The present study was undertaken to test this hypothesis. We studied 22 awake, nonsedated lambs during hypocapnic hypoxia (fraction of inspired O2 = 0.08 during 15 min) induced during the first 72 h of postnatal life. We recorded airflow via a facial mask and pneumotachograph, along with the electromyographic activity (EMG) of the thyroarytenoid muscle (a glottic adductor) in 10 lambs. We also recorded the EMG of both the posterior cricoarytenoid (n = 4) and cricothyroid (n = 5) muscles (glottic abductors), as well as the abdominal muscles (n = 4). We identified typical expiratory airflow braking on the breath-by-breath computed flow-volume loop and thyroarytenoid muscle expiratory EMG as evidence of active expiratory glottic adduction. We found that hypoxia induced a biphasic ventilatory response, with an early peak and a subsequent decrease, and that active expiratory glottic adduction was absent during baseline room-air breathing and hypoxia. We also found that the glottic abductor phasic inspiratory and tonic expiratory EMG as well as the abdominal muscle phasic expiratory EMG, all of which were present during baseline recording, increased during hypoxia. We conclude that hypoxia does not induce expiratory glottic closure in the very first days of life in awake lambs.(ABSTRACT TRUNCATED AT 250 WORDS)