Altered autonomic function and reduced arousability in apparent life-threatening event infants with obstructive sleep...

The aim of this study was to examine cardiorespiratory control in infants presenting with an apparent life-threatening event (ALTE). We performed six to eight 45 degrees head-up tilts in 10 ALTE infants (age, 14 +/- 3 weeks) and 12 age-matched control subjects during slow wave sleep and rapid eye movement sleep (REM). All infants underwent full overnight polygraphic sleep recordings with noninvasive measurement of beat-to-beat blood pressure. All control infants had normal sleep breathing. In contrast, 5 of the 10 ALTE infants had more than two obstructive apneas per hour of sleep, with short hypoxic episodes (obstructive sleep apnea [OSA]). In slow wave sleep, in response to the tilt, the ALTE infants with OSA showed a reduced heart rate response, and three of the five showed a marked postural hypotension. The ALTE infants with OSA also had altered heart rate and blood pressure variability and an increased arousal threshold in REM (p = 0.0002). By contrast, those ALTE infants with normal sleep breathing had cardiovascular and arousal responses similar to those of the control infants. We conclude that a number of ALTE infants with OSA have abnormal cardiovascular autonomic control that, combined with their decreased arousability in REM, may provide an explanation for the ALTE episodes.