Adaptive variation in the mammalian respiratory system in relation to energetic demand: II. Reaching the limits to oxygen flow

摘要: Abstract We address the quesion of how animals adjust steady-state rates oxygen transport from lungs to mitochondria over a range exercise intensities rest upper limit (V O 2 max). Convective in circulation is central this process, establishing boundary condition for pressure heads diffusion lung and tissues. Athletic dogs ponies are compared less athletic same size, goats calves. find: (1) V max reached after 29-fold increase predicted resting levels species, while goat calf capable only 12-fold increase; (2) cardiac output most important variable controlling flow through circulation; (3) adjustments brought about primarily by changing heart rate; (4) difference arteriovenous content also dynamic regulator flow, increasing with intensity due both an concentration circulating erythrocytes more blood flowing active models; (5) head tissues increases durign as result increased hyperventilation.