Ventilation and carotid chemoreceptor discharge during venous CO2 loading via the gut.

A simple method of loading CO2 into the venous blood of anaesthetized or decerebrate cats is described. Heated humidified gas of high CO2 content is passed retrogradely through the gut. This increases CO2 elimination from the lungs by 1.8 to 3.6 fold, minute ventilation by 1.5 to 2.7 fold and cardiac output by 1.1 to 1.6 fold. This method of venous CO2 loading allows the recording of afferent nerve impulses. We show that it has little effect on the mean discharge frequency of carotid body chemoreceptors when end-tidal gases are held constant, but that it enhances greatly the amplitude of the respiratory oscillation of their discharge.