Maturation of the ventilatory response to CO2 in the newborn piglet.

In 12 piglets aged 0 to 1.5 d, we assessed the contribution of the peripheral and central chemoreceptors in mediating the ventilatory response to CO2 and the apneic threshold during normoxia (arterial O2 tension, 13 kPa) using the dynamic end-tidal forcing technique. With this technique, the ventilatory response is separated into a peripheral and a central component using a two-compartment model. Each component is described by a CO2 sensitivity, a time constant, a transport delay time, and an apneic threshold. The means of the estimated parameters per piglet were compared with those obtained in a previous study in piglets aged 2 to 11 d (Wolsink JG, Berkenbosch A, DeGoede J, Olievier CN: J Physiol (Lond) 456:39-48, 1992). The ratio of the peripheral CO2 sensitivity to the total CO2 sensitivity was found to be significantly lower in the younger group of piglets (0.14 +/- 0.10 versus 0.29 +/- 0.10), whereas the apneic threshold was significantly higher (2.52 +/- 1.12 kPa versus 1.06 +/- 1.46 kPa). We conclude that the peripheral chemoreceptors are responsive to CO2 shortly after birth. However, the ventilatory response to CO2 maturates in the first few days after birth by an increase in the relative contribution of the peripheral chemoreceptors to the total ventilatory response and a decreasing apneic threshold.