Combined effects of hypoxia and moderate heat load on ventilation in awake Pekin ducks

In awake Perkin ducks breathin an hypoxic gas mixture ( P I O 2 = 83 Torr ) ventilatory pattern, respiratory gas exchanges, respiratory water loss (M R H 2 O), arterial blood P O 2 and P CO 2, and pH were measured first at 20 °C ambient temperature, then after 2–4-hr exposure at 25, 30 or 35°C. Results were compared with those previously obtained in similar experiments on normoxic ducks P I O 2 = 145 Torr ). At 20 °C, the body temperature (Tb), oxygen consumption (M O 2) and M R H 2 O were identical in hypoxic and normoxic ducks. Hypoxic animals hyperventilated; arterial P CO 2 was about 8 Torr lower and arterial pH 0.09 unit higher than in normoxic ones. During heat loads, M O 2 remained unchanged nad M R H 2 O increased to the same extent in hypoxic and normoxic ducks, but the thermoregulatory ventilatory responses differed greatly. At 35 °C, hypoxic ducks panted sluggishly: respiratory frequency, f, was about 160 min −1, and ventilatory minute volume, V̇, increased 2.7 fold; Tb rose by 1 °C. Normoxic ducks panted vigorously: f rose to 260 min −1, and V̇ increased 6.5 fold; Tb did not rise. Arterial P CO 2 and pH in both groups shifted only slightly toward alkalotic values. It is concluded that in awake Pekin ducks exposed to the combined effects of hypoxia and moderate heat load, mechanisms regulating the O 2 and CO 2 ventilatory convection may set aside the normal thermal panting, and may have priority over mechanisms regulation the body temperature.