Respiratory response to arterial H⁺ at different levels of arterial$P_{{\text{CO}}_{\text{2}} }$ during hyperoxia or hypoxia

Summary

Experiments were carried out in 12 dogs anesthetized with halothane of constant alveolar concentration (mean: 0.89%). The ventilatory response to arterial$P_{{\text{CO}}_{\text{2}} }$ with hyperoxia was determined in metabolic acidosis (by infusion of 0.5 N HCl solution). The ventilatory response to arterial$P_{{\text{CO}}_{\text{2}} }$ with constant hypoxia (about 50 mm Hg arterial$P_{{\text{O}}_{\text{2}} }$) was determined in both metabolic acidosis and alkalosis (by infusion of 1 M NaHCO₃ solution).

The arterial H⁺-ventilation response curve was obtained at different constant levels of$P_{{\text{CO}}_{\text{2}} }$ by simultaneous analysis of the$P_{{\text{CO}}_{\text{2}} }$-H⁺ diagram and the$P_{{\text{CO}}_{\text{2}} }$-ventilation response curve. Ventilation in hyperoxia was largely dependent on$P_{{\text{CO}}_{\text{2}} }$ if acid-base balance was near normal, but became independent of$P_{{\text{CO}}_{\text{2}} }$ and dependent on arterial H⁺ as this increased. It was postulated that this was partly due to the negative interaction between$P_{{\text{CO}}_{\text{2}} }$ and H⁺. The H⁺-ventilation response curves showed the same pattern in hypoxia, but only on the alkalotic side. However, with hypoxia in the range of normal to acidotic condition, control of ventilation was mainly dependent on H⁺ and independent of$P_{{\text{CO}}_{\text{2}} }$; this implies an interaction between hypoxia and H⁺ at the peripheral chemoreceptors.