Role of carbon dioxide oscillation in the control of respiration in the anesthetized dog.

In order to examine the role of respiratory oscillation of PaCO2 (CO2 oscillation) in the control of respiration, we performed veno-venous bypass using a membrane lung in 10 anesthetized paralyzed dogs, where the dog was put on fixed mechanical ventilation so that we could keep average PaCO2 and PaO2 constant by adjusting FICO2 and FIO2 during CO2 loading/unloading. By venous CO2 loading/unloading we could widely change the CO2 output from the lung (11-440% of the control) resulting in large changes in the arterial CO2 oscillations (50-280% of the control for the maximum rate of rise of PaCO2 and 40-350% of the control for the maximum rate of fall of PaCO2), which was measured by a rapidly responding intra-arterial pH electrode. Despite such wide variations in CO2 oscillations we did not find any consistent change in the respiratory center output (minute phrenic activity). This held true after compensating the changes in the minute phrenic activity for the CO2 sensitivity of each individual dog. Thus, the present results may suggest that the CO2 oscillation plays little role in the control of respiration in mild increase in VCO2.