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 ventilator y response to CO2 at three levels of arterial O2 tension using the dyn amic 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 sensitiv ity, a time constant, a transport time and a single apnoeic threshold. The results showed that the sensitivity of the peripheral chemorecept ors significantly (P < 0.01) increased from 25.0 +/- 23.6 ml.min-1.kPa -1.kg-1 (mean +/- SD) during normoxia (Pa(O2) = 12.8 +/- 0.3 kPa) to 4 2.5 +/- 29.4 ml.min-1.kPa-1.kg-1 during moderate hypoxia (Pa(O2) = 8.8 +/- 0.4 kPa) and to 80.2 +/- 44.4 ml.min-1.kPa-1.kg-1 at severe hypox ia (Pa(O2) = 5.1 +/- 0.3 kPa). There was no significant effect of the level of Pa(O2) on the other parameters. The results were compared wit h those obtained in a previous study in piglets aged 2-11 days. It sho wed that the interaction strength at the level of the peripheral chemo receptors, defined as the negative ratio of the change in the peripher al CO2 sensitivity to the change in Pa(O2) 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 t he level of the peripheral chemoreceptors is already developed shortly after birth and becomes smaller during development.