Control of ventilation during intravenous CO2 loading in the awake dog

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Abstract
The ventilatory response to venous CO2 loading and its effect on arterial CO2 tension was determined in 5 awake dogs. Blood, 200-500 ml/min, was diverted from a catheter in the right common carotid artery through a membrane gas exchanger and returned to the right jugular vein. CO2 loading was accomplished by changing the gas ventilating the gas exchanger from a mixture of 5% CO2 in air to 100% CO2. The ventilatory responses to this procedure were compared with those resulting from increased inspired CO2 concentrations (during which ventilation of the gas exchanger with the air and 5% CO2 mixture continued). The ventilatory response to each form of CO2 loading was computed as .DELTA..ovrhdot.VE/.DELTA.PaCO2 [change in expired ventilation/change in arterial CO2 partial pressure]. The mean ventilatory response to airway CO2 loading was 1.61 l/min per Towr PaCO2 [arterial CO2 partial pressure]. The mean response for the venous CO2 loading was significantly higher and not significantly different from infinite CO2 sensitivity (i.e., isocapnic response). The results provide further evidence for a CO2-linked hyperpnea, not mediated by significant changes in mean PaCO2.