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% O2 was measured during quiet sleep. Arterial SaO2 (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 predominantely 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 O2 chemoreflex is slower than previously thought.
Cohen
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Department of Obstetrics and Gynaecology, King George V Memorial Hospital, New South Wales, Australia.
Malcolm
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Henderson-Smart
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D000375:Aging / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007223:Infant; D007231:Infant, Newborn / Q000502:physiology*; D010092:Oximetry; D012123:Pulmonary Ventilation / Q000502:physiology*; D015203:Reproducibility of Results; D012890:Sleep / Q000502:physiology; D013997:Time Factors