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Ventilatory response of the newborn infant to mild hypoxia
G Cohen1, G Malcolm, D Henderson-Smart
1Department of Obstetrics and Gynaecology, King George V Memorial Hospital, New South Wales, Australia.
Insights
Newborn infants
Area of Science:
- Neonatal physiology
- Respiratory control
- Cardiorespiratory adaptation
Background:
- The transition from immature to mature ventilatory responses to hypoxia is crucial for newborn adaptation.
- Previous assumptions suggested this maturation occurs by postnatal day 10.
- This study systematically re-evaluated the developmental timeline of hypoxic ventilatory response.
Purpose of the Study:
- To investigate the developmental trajectory of the ventilatory response to sustained hypoxia in term infants.
- To determine if the mature hyperpneic response is established by postnatal day 10.
- To provide a more systematic assessment of O2 chemoreflex maturation.
Main Methods:
- Studied seven healthy term infants aged 2 days to 8 weeks.
- Measured ventilatory response (VR) to 5 minutes of 15% O2 breathing during quiet sleep.
- Continuously monitored arterial oxygen saturation (SaO2) and minute ventilation (delta V'i).
Main Results:
- Younger infants (2-3 days) showed a sustained hypopneic response to hypoxia.
- Older infants (8 weeks) exhibited a biphasic response, with initial hyperpnea followed by hypopnea.
- A statistically significant age-related difference in VR was observed (P < 0.05).
Conclusions:
- Term infants may retain an immature ventilatory response to mild hypoxia for up to 2 months post-birth.
- Postnatal development of the O2 chemoreflex appears slower than previously believed.
- Ambient conditions and quiet sleep influence the observed hypoxic ventilatory response.
Abstract:
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.