ABSTRACT
Oxygen consumption, respiratory evaporative water loss, respiratory rate and gas tensions in the clavicular and abdominal air sacs and in arterial blood were monitored after occluding either the cranial thoracic air sac only (CRT group) or the cranial and caudal thoracic air sacs together (CRT-CT group). Respiratory water loss was used to estimate minute ventilation. Both experimental groups were able to maintain control levels of ventilation at rest and during treadmill exercise at approximately three times the resting metabolic rate. The CRT group regulated blood and intrapulmonary 
and 
normally, but there was a slight hypoxaemia/hypercapnaemia in the CRT-CT group, apparently as a result of parabronchial hypoventilation. The differential distribution of gas tensions between the cranial and caudal groups of air sacs was the same in control and experimental birds, suggesting that a normal intrapulmonary airflow pattern was preserved in the absence of the thoracic air sacs. The findings are discussed in the light of current models of the control of intrapulmonary airflow in birds.
