Changes in the VI-VCO2 relationship during exercise in goats: role of carotid bodies

To assess the role of carotid bodies in modulating the ventilation-CO2 production relationship, steady-state responses to mild exercise were determined in goats following several experimental manipulations that led to chronic changes in resting ventilation and arterial blood gases. The experimental conditions were 1) control, 2) whole body serotonin depletion (induced by p-chlorophenylalanine, 100 mg/kg), 3) carotid body denervation (CBX), and 4) serotonin depletion with CBX. Resting values of arterial CO2 pressure (Pco2) ranged from 32 to 48 Torr. In each condition, arterial Pco2 was regulated to a similar degree in exercise due to changes in the slope of the ventilation-CO2 production relationship (delta Vi/delta Vco2) in accordance with the requirements of gas exchange. delta Vi/delta Vco2 increased with serotonin depletion both before and after CBX. The principal component of ventilation contributing to changes in delta Vi/delta Vco2 was tidal volume. These results suggest a basic property of the ventilatory control system whereby enhanced ventilatory activity at rest is associated with an increased ventilatory response to exercise via a mechanism that does not require peripheral chemoreceptors.