Effects of CO2 and H+ on the ventilatory response to peripheral chemoreceptor stimulation.

ABSTRACT

To determine whether the stimulatory effect of CO2 on the peripheral chemoreceptors is due to molecular CO2, H+ or both we measured steady-state ventilation (Ve) during normoxia in 9 and during hypoxia in 5 chloralose-urethane anaesthetized cats using the artificial brain stem perfusion technique. This technique allows one to manipulate independently the PaCO2, PaO2 and the pHa of the blood in the systemic circulation (peripheral) and the blood perfusing the brain stem (central). Keeping the central conditions constant the H+ and CO2 concentrations in the systemic circulation were changed by i.v. infusion of 0.3 M HCl or 0.6 M NaHCO3 and by giving the animal different CO2 mixtures to inhale. The peripheral H+ concentration ([H+]p) range covered was from 27 to 103 nmol X 1(-1); the peripheral arterial CO2 tension (PaPCO2) ranged from 2.3 kPa to 8.4 kPa. Fitting the data with the function VE = a[H+]p + bPaPCO2 + c revealed that the coefficient b was not significantly different from zero at the 0.05 level during normoxia and hypoxia. The mean value (+/- SEM) found for the coefficient a was 33.0 +/- 3.6 at normoxia and 36.0 +/- 15.4 ml X min-1 X nM-1 at hypoxia. We conclude that the steady-state ventilatory response due to the stimulation of the peripheral chemoreceptors with CO2 is mediated by H+. The effects of molecular CO2 are negligible.