Mammalian locomotor-respiratory integration: implications for diaphragmatic and pulmonary design.

Diaphragmatic function and intrapulmonary respiratory flow in running mammals were found to differ substantially from the corresponding conditions known in resting mammals. In trotting dogs, orbital oscillations of the diaphragm were driven by inertial displacements of the viscera induced by locomotion. In turn, oscillations of the visceral mass drove pulmonary ventilation independent of diaphragmatic contractions, which primarily served to modulate visceral kinetics. Visceral displacements and loading of the anterior chest wall by the forelimbs are among the factors that contribute to an asynchronous ventilation of the lungs and interlobar gas recycling. Basic features of mammalian respiratory design, including the structure of the diaphragm and lobation of the lungs, appear to reflect the mechanical requirements of locomotor-respiratory integration.