Obstructive apnea, associated patterns of movement, heart rate, and oxygenation in infants at low and increased risk for SIDS.

Repetitive polysomnograms were recorded between 40 weeks post-conceptional age and 6 months in a total of 49 infants, 19 healthy preterm infants, 14 normal term infants, and 16 subsequent siblings of infants who died of sudden infant death syndrome (SIDS). These nighttime recordings lasted 2-4 hours, except at 3 months when an overnight 12-hour recording was performed. Obstructive apneas (OA) > 3 seconds were divided into 3 categories: 1) clear obstructive, 2) mixed and 3) unclear because of movement artifacts. More than half belonged in category 3 and were excluded from further analysis unless accompanied by a transient episode of bradycardia (TEB), defined as heart rate < or = 100 beats per minute. Each OA with TEB was also examined for changes in transcutaneous oxygen tension (PtcO2). Most pauses were brief (median, 4 seconds), the longest (27 seconds) seen only once in the youngest premature infant. The majority of OA were accompanied by heart rate accelerations. The number of clear obstructive and mixed apneas was similar. The scores were combined to calculate a density (number per 100 minutes of recording). OA were not common: Their density decreased from 2 in 100 minutes at 40 weeks in the preterm to once every 300 minutes (5 hours) in the 6-month-old term infant. Ten percent of the OA were accompanied by TEB. Of these, 10% were accompanied by a PtcO2 decrease of > 10 mm Hg. OA with TEB followed a nonmonotonic curve, the highest percentage of infants showing this pattern at the age of highest risk for SIDS. Minor differences among study groups were confined to less movements with OA in subsequent siblings and an earlier peak incidence of OA with TEB in prematures, compared to normal term infants. OA were seen in all study groups, were self-limited, and apparently were devoid of pathological consequences.