Ventilatory interaction between hypoxia and hypercapnia in piglets shortly after birth

In 12 piglets aged 0-1.5 days we assessed the relative contribution of the peripheral and central chemoreceptors in mediating the ventilatory response to CO2 at three levels of arterial O2 tension 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 time and a single apnoeic threshold. The results showed that the sensitivity of the peripheral chemoreceptors significantly (P < 0.01) increased from 25.0 +/- 23.6 ml.min-1.kPa-1.kg-1 (mean +/- SD) during normoxia (PaO2 = 12.8 +/- 0.3 kPa) to 42.5 +/- 29.4 ml.min-1.kPa-1.kg-1 during moderate hypoxia (PaO2 = 8.8 +/- 0.4 kPa) and to 80.2 +/- 44.4 ml.min-1.kPa-1.kg-1 at severe hypoxia (PaO2 = 5.1 +/- 0.3 kPa). There was no significant effect of the level of PaO2 on the other parameters. The results were compared with those obtained in a previous study in piglets aged 2-11 days. It showed that the interaction strength at the level of the peripheral chemoreceptors, defined as the negative ratio of the change in the peripheral CO2 sensitivity to the changes in PaO2 was greater in the younger piglets. From these results we conclude that in the newborn piglet the positive ventilatory interaction between hypoxia and hypercapnia at the level of the peripheral chemoreceptors is already developed shortly after birth and becomes smaller during development.