Arterial and mixed venous blood gas tensions in exercising ducks

Adult White Pekin ducks were exercised at three work levels on a treadmill at speeds of .9, 1.47, and 2.16 km/hr for 20 min with a 90 min rest period following each exercise period. Blood gas and pH analyses were performed on samples simultaneously withdrawn from the brachial artery and the right ventricle (as an estimate of mixed venous blood) at predetermined intervals during the experiment. Both arterial and mixed venous PCO2 significantly decreased with the increases in the level of exercise. Arterial pH did not change significantly from resting values at any level of exercise. Mixed venous pH decreased at the onset of exercise but returned to near resting value by the end of each exercise period. These measurements indicate that ducks increase their ventilation during exercise above that required to eliminate the generated CO2. Because the increased ventilation produces a reduction in arterial PCO2, it is unlikely that peripheral or central CO2-sensitive chemoreceptors are responsible for the ventilatory drive.