Respiratory and cardiovascular responses to exercise in the duck.

Adult White Pekin ducks were exercised for 20 min on a treadmill (3 degrees incline) at two speeds: 0.9 and 1.47 km/h. Each exercise period was followed by a 90-min rest. Heart rate and systolic and diastolic blood pressure increased significantly during each exercise period. During exercise, tidal volume decreased and respiratory frequency increased. Minute ventilation markedly increased at the onset of exercise and continued to increase throughout, whereas clavicular air sac PCO2 (PCSCO2) decreased. Both PACO2 and PVCO2 decreased as the running speed increased. pHv decreased at the onset of exercise, but returned to near resting values by the end of an exercise period. During either exercise period pHa did not significantly change from control values. PAO2 exhibited significant increases at both exercise speeds. Both arterial and mixed venous plasma [HCO3-] decreased significantly with each exercise period. Body temperature increased 1-2 degrees C during each run. Because the increased ventilation produced a reduction in PaCO2 and Pcsco2, it is unlikely that peripheral or central CO2 receptors were responsible for the ventilatory drive: that drive may result from hyperthermia or activity of certain muscle afferents.