Ventilatory response of the newborn infant to mild hypoxia

The transition from an immature (biphasic) to a mature (sustained hyperpneic) response to a brief period of sustained hypoxia is believed to be well advanced by postnatal day 10 for newborn infants. However, a review of the supporting evidence convinced us that this issue warranted further, more systematic investigation. Seven healthy term infants aged 2 days to 8 weeks were studied. The ventilatory response (VR) elicited by 5 min breathing of 15% O-2 was measured during quiet sleep. Arterial S-aO2 (pulse oximeter) and minute ventilation (expressed as a change from control, Delta V-i') were measured continuously. infants were wrapped in their usual bedding and slept in open cots at room temperature (23 degrees-25 degrees). Infants aged 2-3 days exhibited predominately a sustained hypopnea during the period of hypoxia (Delta V-i' = -2% at 1 min, -13% at 5 min). At 8 weeks of age, the mean response was typically biphasic (Delta V-i' = +9% at 1 min, -4% at 5 min). This age-related difference between responses was statistically significant (two-way ANOVA by time and age-group; interaction P < 0.05). These data reveal that term infants studied under ambient conditions during defined quiet sleep may exhibit an immature VR to mild, sustained hypoxia for at least 2 months after birth. This suggests that postnatal development of the O-2 chemoreflex is slower than previously thought. (C) 1997 Wiley-Liss, Inc.