Postnatal ventilatory response to CO₂ in awake piglets.

Abnormal ventilatory responses to increased levels of inspired CO₂ during postnatal development may pose a risk for Sudden Infant Death Syndrome, primarily during periods of vulnerability. The purpose of this study was to test the hypothesis that in awake piglets the ventilatory response to hypercapnia would be attenuated between 10 and 15 days of age relative to younger and older ages. To test this hypothesis, we measured the ventilatory response to 5% inspired CO₂ in piglets from postnatal (PN) days 1 through PN28. Piglets were divided into groups and exposed to 5% CO₂ daily, every 3rd day or on and after PN20-21 only to avoid any plasticity that may result from repeated exposure to CO₂. Room air ventilation normalized to body weight (V˙(E), ml/min/kg) declined with postnatal age in piglets from all groups. The ventilatory response to 5% inspired CO₂ (expressed as % change from control) was present at birth, and we did not find an age-dependent change from PN1 to PN28 (p > 0.1). In addition, we did not find that repeated exposure (daily or every 3rd day) to 5% inspired CO₂ altered the ventilatory response during this period of development. We conclude that the previously documented apparent critical period of development in piglets between 10 and 15 days of age is not associated with attenuation of the ventilatory response to 5% inspired CO₂.