Arousal and Cardiorespiratory Responses to Airflow Obstruction in Sleeping Lambs: Effects of Sleep State, Age, and Repeated Obstruction

We studied the effects of postnatal age on arousal and cardiorespiratory responses to airflow obstruction in sleeping lambs: we also determined the influence of sleep states and repeated airflow obstruction. Sixteen lambs were chronically prepared for monitoring sleep states, arterial O2 saturation (SaO2), heart rate (HR), and intrapleural pressure (Pp1) and were studied from 2-29 days after birth. Obstruction of respiratory airflow by facemask occlusion led to arterial desaturation, augmentation of respiratory efforts, bradycardia, and arousal. Lambs aroused more rapidly and with less desaturation in non-rapid eye movement (NREM) sleep (7 +/- 1 second and 7 +/- 1%, respectively) than in rapid eye movement (REM) sleep (18 +/- 2 seconds and 22 +/- 2%), and cardiac slowing was less in NREM than in REM sleep. In REM sleep only, the arousal latency and desaturation at arousal were affected by postnatal age; arousal responses occurred most rapidly in the youngest (< or = 6 days) and oldest (> or = 13 days) age groups and were delayed at 7-12 days. Repeated episodes of airflow obstruction led to reduced arousability in REM sleep only. We conclude that arousal from REM. but not NREM, sleep in response to the obstruction of respiratory airflow is transiently depressed during early postnatal development and that repeated obstructions and arousals also lead to depressed arousal from REM sleep.