Metabolic and ventilatory responses to CO hypoxia at different levels of oxygenation in the rat

Adult, conscious rats have been exposed to CO-induced hypoxia for 30 min in normoxia, ambient hypoxia (FI_O2=14%), or hyperoxia (FI_O2=40%). From arterial blood gas analyses, FICO was adjusted in all experimental conditions to obtain final arterial oxygen saturations (Sa_O2) of ∼60%. Oxygen uptake (), ventilation ($\text{V}\text{̇}$) and colonic temperature (Tc) were measured in experiments carried out at an ambient temperature of either 25 or 15 °C. It was found that CO hypoxia induced marked reductions in the hemoglobin O₂ half saturation pressure (P₅₀). Furthermore, isolated reductions in Sa_O2 (with Pa_O2 constant) induced decreases in and Tc and increases in ventilation which, as compared with normoxia, were enhanced in ambient hypoxia and reduced but still significant in hyperoxia. As suggested by previous studies, the interactions between Sa_O2 and Pa_O2 which operate on the control of metabolism and ventilation originate probably in the central nervous system.