The natural history of the appearance of apnea of prematurity.

Twenty healthy preterm infants of less than 34 wk gestation were studied with continuous recordings, commencing within 8 h of birth, for up to 1 wk of age to determine the usual time course of the appearance of apnea and to classify apnea types. Airway occlusion studies were also performed on a regular basis to determine whether apneic spells were preceded or followed by a reduction in central respiratory drive. Apneic spells of greater than 15 s duration accompanied by hypoxia or bradycardia occurred in all infants before 24 h of age. The frequency of apneic spells was highest in the first 24 h after birth with a mean frequency of 0.9/h and gradually reduced thereafter, falling to 0.2/h by 5 d of age (p less than 0.01). Apneic spells were more likely to be obstructive in the first 2 d of life than thereafter (p less than 0.05). Central apnea was proportionately significantly less frequent during this time period. Reduced respiratory drive, as demonstrated by airway occlusion pressures, was associated with more frequent apnea and was evident at the first occlusion study, which frequently preceded the first significant apnea.