Understanding the limitation of O2 supply through comparative physiology

Comparative physiology and morphometry are used to explore the role of the lung in the limitation of oxygen supply to working muscle as it is experienced at aerobic capacity and in hypoxia such as at high altitude or in subterraneous burrows. In the human lung, as in that of most mammals, the pulmonary diffusing capacity is about 1.5 times larger than what is needed at aerobic capacity. In athletic species (horse, dog) there is no such excess diffusing capacity. As an exception the pronghorn antelope from the Rocky Mountains is a high performance athletic mammal whose lung shows an excess diffusing capacity. This is interpreted as a means to develop hypoxia tolerance as this animal performs its vigorous runs at high altitude. Information on the fossorial mole rat demonstrates that the lung's diffusing capacity is important in developing hypoxia tolerance. It is concluded that the lung is designed in relation to both internal and external constraints.