INFLUENCE OF SLEEP STATES ON LARYNGEAL AND ABDOMINAL MUSCLE RESPONSE TO UPPER AIRWAY OCCLUSION IN LAMBS

This study was aimed at describing abdominal and laryngeal muscle resp onses to upper airway occlusion (UAO) in early life and the effect of sleep states on these responses. Twelve nonsedated, 9-26-d-old lambs w ere studied. We simultaneously recorded 1) airflow (pneumotachograph face mask); 2) sleep states (electrocorticogram and electrooculogram) ; 3) abdominal muscle (external obliquus) electromyogram (EMG); and 4) glottic constrictor (thyroarytenoid) and dilator (posterior cricoaryt enoid and cricothyroid) muscle EMGs. The pneumotachograph was repeated ly occluded for 15-30 s in wakefulness and natural sleep. We analyzed 90 occlusions during wakefulness (11 lambs), 28 during non-rapid eye m ovement (nREM) sleep (six lambs), and 23 during rapid eye movement (RE M) sleep (five lambs). A phasic expiratory external obliquus EMG was p resent during baseline and progressively increased throughout UAO in w akefulness and nREM sleep, but not in REM sleep. Phasic thyroarytenoid EMG progressively increased during inspiratory efforts throughout UAO in wakefulness and nREM sleep, paralleling the increase in glottic di lator (posterior cricoarytenoid and cricothyroid) EMG. In contrast, gl ottic muscle response to UAO in REM sleep was severely blunted or diso rganized by frequent swallowing movements. We conclude that UAO trigge rs complex and coordinated laryngeal and abdominal muscle responses du ring wakefulness and nREM sleep in lambs; these responses are largely absent, however, in REM sleep. These unique results, together with the defective arousal response in REM sleep, suggest that vulnerability t o airway occlusion could be increased during REM sleep in early life. Possible implications for understanding severe postnatal apneas are di scussed.