1 Section of Physiology, Mayo Clinic and Mayo Foundation, Rochester, Minnesota
During exercise the normal pulmonary vessels can accommodate a three to fourfold increase in flow with about a 50 per cent increase in perfusion pressure. There is about a 10 per cent increase in the total volume of blood in the lungs, which may be accounted for mainly by an increase in capillary blood volume. The diffusion capacity is increased, the concentration of red blood cells is increased, and a relatively uniform ventilation-perfusion ratio is achieved throughout the lung.