Upper airway resistance in infants at risk for sudden infant death syndrome.

To investigate the relationship between sudden infant death syndrome and upper airway obstruction, we studied 14 term infants at a mean age of 11 weeks who had been identified as being at risk for sudden infant death syndrome on the basis of clinical and family histories and polygraphic monitoring. Respiratory efforts during sleep were investigated by esophageal pressure monitoring (all 14 infants) and by monitoring of flow with a pneumotachometer (6 infants). During apparently normal sleep, increased respiratory efforts were shown by intermittent increases in the magnitude of the negativity of esophageal pressure. Mild changes in tidal volume occurred occasionally, always at the lowest monitored esophageal pressure of a breath sequence. These tidal volume decreases had no impact on oxygen saturation but led to a short arousal and decreased respiratory efforts, followed by a return to normal breathing. Occasionally the abnormal increase in upper airway resistance did not lead to an immediate arousal but instead to a short obstructive apnea that was then followed by an arousal. This investigation indicates the importance of arousal mechanisms in maintaining normal breathing during sleep. Any disruption of the arousal mechanisms during sleep (including sleep fragmentation caused by repetitive arousals) may place these infants with increased upper airway resistance at risk for obstructive apnea during sleep.