Heart rate and respiratory rate differences between preterm and full-term infants during quiet sleep: possible implications for sudden infant death syndrome.

The heart rate and respiratory rate of eight preterm (average gestational age, 33.3 +/- 2.2 weeks) and 13 full-term infants were determined during quiet sleep at home during the first year of life. Both heart rate and respiratory rate were greater in preterm infants throughout the first six months. The difference was maximum at age 10 weeks (21.2 beats per minute and 13.7 breaths per minute), with the difference being statistically significant, at least at the P less than .01 level at ages 10, 12 and 14 weeks, while P greater than or equal to .01 at all other ages. The 10- to 14-week period is precisely the same period during which the incidence of sudden infant death syndrome (SIDS) has been reported to be maximum. These results support the concept that SIDS is linked to a vulnerable phase of cardiorespiratory maturation.