Sleep state, apnea and bradycardia in pre-term infants.

Respiratory pattern and heart rate were studied in 28 pre-term infants and four full-term infants during the first weeks of life. Sleep state was identified by standard neurological and EEG criteria. Apneic spells lasting 10 seconds or more were most frequent in the least mature infants, and their frequency tended to diminish with increasing maturity. When these apneic attacks were related to sleep state they were found to occur more frequently during non-REM sleep in infants of 30 to 33 weeks gestation. This was the only statistically significant difference found. No over-all pattern relating sleep state to frequency of apnea could be detected for individual infants. It was also difficult to relate the occurrence of bradycardia to apnea in terms of sleep state or gestational age. It is concluded that no simple relationship between sleep state, apnea and bradycardia exists and that a complex interrelation between central and peripheral factors is involved in these events.