Ventilatory interaction between oxygen and carbon dioxide in the preterm primate.

The steady state ventilatory response to inhaled CO2 was measured in eleven unanesthetized premature Macaca nemestrina during the first 3 wk of life in different steady state background O2 mixtures hypoxia (FIO2 = 0.08 or 0.12), normoxia (FIO2 = 0.21) and hyperoxia (FIO2 = 0.96). Hyperoxic delta VI/delta PACO2 and delta P0.2/ delta PACO2 were significantly greater than hypoxic delta VI/ delta PACO2 and delta P0.2/delta PACO2, respectively, at both 2 and 21 days postnatal age by the Mann Whitney test of nonparametric ranking (2 days: 89.. and 80.2 degrees versus 88.7 and 56.4 degrees, respectively; 21 days: 89.3 and 76.6 degrees versus 50.2 and 57.1 degrees, respectively; p less than 0.05). Hypoxic delta VI/delta PACO2 was significantly depressed compared to normoxic delta VI/ delta PACO2 only at 21 days of age (50.2 versus 89.4 degrees, respectively; p less than 0.05); hyperoxic CO2 sensitivity and normoxic CO2 sensitivity did not differ at either age. The ventilatory interaction between O2-CO2 in the neonatal primate appears to be the inverse of the typical adult ventilatory interaction. It is hypothesized that differential changes in brain stem blood flow between neonates and adults might explain this difference in O2-CO2 ventilatory interaction.