Hypoxia has a greater effect than exercise on the redistribution of pulmonary blood flow in swine

Strenuous exercise combined with hypoxia is implicated in the development of high-altitude pulmonary edema (HAPE), which is believed to result from rupture of pulmonary capillaries secondary to high vascular pressures. The relative importance of hypoxia and exercise in altering the distribution of pulmonary blood flow (PBF) is unknown. Six chronically catheterized specific pathogen-free Yorkshire hybrid pigs (25.5 ± 0.7 kg, means ± SD) underwent incremental treadmill exercise tests in normoxia (FiO2 = 0.21) and hypoxia (FiO2 = 0.125, balanced order), consisting of 5 min at 30, 60, and 90% of the previously determined Vo2max. At steady state (∼4 min), metabolic and cardiac output data were collected and fluorescent microspheres were injected over ∼30 s. Later the fluorescent intensity of each color in each 2-cm3 lung piece was determined and regional perfusion was calculated from the weight-normalized fluorescence. Both hypoxia and exercise shifted PBF away from the ventral cranial lung regions toward the...