Maturation of cardiac control in full-term and preterm infants during sleep.

ECG and respiration were recorded from 13 full-term and 8 preterm infants at 2-5 week intervals during sleep at home in the first year of life. Average pulse interval in both quiet and active sleep was minimum at postnatal ages between 4 and 10 weeks, with the minimum during quiet sleep being significantly smaller for preterm (409 +/- 22 (SE) msec) than for full-term (445 +/- 9 msec) infants. The minimum average pulse interval of preterm infants was smaller than the pulse interval of full-term infants at any post-conceptional age, and a smaller average pulse interval and smaller variations in pulse interval in preterm infants during quiet sleep persisted until a postnatal age of 7 months. The pulse interval variations attributable to respiration varied substantially with age. The results indicate that developmental changes in cardiac rate control are functions of both postnatal and post-conceptional age, with the post-conceptional age at birth setting the mean level of pulse interval, a level which is then altered by development linked to postnatal age.