Differential effects of CO2 and H+ as central stimuli of respiration in the cat

Effects of H+ and CO2 as independent stimuli of central respiratory chemoreceptors were studied in anesthetized cats in which pH and PCO2 on the ventral surface of the medulla (pHe and PeCO2) could be monitored in response to intravenous acid infusion or CO2 inhalation or to a combination of CO2 inhalation and base infusion that allowed PeCO2 to vary at constant pHe. Respiratory responses to these changes were monitored by measuring tidal volume (VT), respiratory frequency (f), and total ventilation. Respiratory acidosis stimulated ventilation by increasing both VT and f. Mild metabolic acidosis (decrease in pHe less than 0.05) exerted similar effects, but more severe metabolic acidosis failed to produce further stimulation. Increasing or decreasing PeCO2 at constant pHe caused pronounced increases or decreases in respiration mediated both by VT and f. For the same change in PeCO2 the respiratory effects were, however, less pronounced when pHe was kept constant than when pHe was allowed to change with PeCO2. The results suggest that both CO2 and H+ exert independent effects on respiration via central chemoreceptors.