Ventilatory and circulatory changes during cold exposure in the Pekin duck Anas platyrhynchos

Inspired ventilation (VI), O2 uptake (VO2), body temperature (TB), arterial blood pressure and arterio-venous differences in blood gases and pH were measured in ducks. Anas platyrhynchos, during exposure to variable ambient temperature (Ta) +20, 0 and -20 degrees C. A stable TB was maintained at all Ta's VO2 increased from 12.07 ml O2 (STPD) X kg-1 X min-1 at 20 degrees C to 28.95 ml O2 X kg-1 X min-1 at 20 degrees C. The ventilatory requirement (VI/VO2) changed from 0.468 L X mmol-1 at 20 degrees C to 0.322 L X mmol-1 at -20 degrees C corresponding to a change in overall O2-extraction from 28.5 to 41.4%. The increase in VI during cold exposure resulted from an increased tidal volume while breathing frequency was unchanged. This caused a smaller fraction of the total inspired air being dead space ventilation during cold exposure. The changed ventilatory requirement was largely the result of an increased parabronchial O2-extraction, whereas the altered ventilatory pattern accounted for a smaller part (21%) of the decreased ventilatory requirement. Arterial and venous O2 content and PaO2 changed little with cold exposure while PVO2 increased significantly. Calculated values for cardiac output increased from 173.7 ml X kg-1 X min-1 at +20 degrees C to 431.4 ml X kg-1 at -20 degrees C. From a thermoregulatory point of view it seems significant that the increased heat production during cold exposure is followed by an increased oxygen extraction in the lungs and in increased cardiac output, rather than by a further elevation of ventilation.