Regional circulatory responses to 96 hours of hypoxia in conscious sheep

Exposure of adult ewes to normobaric hypoxia (Pa_O2 40 mm Hg) for 96 h led to increases of V̇E(+54%), while V̇_O2 decreased Pa_CO2 declined progressively to stabilized at 24(±1.5 SE) mm Hg by 24-48 h. Cardiac output (thermodilution) was elavated temporarily for 24 h (23-34%) but then returned to normoxic levels, while heart rate (28-42%) and pulmonary artery pressure (38-56%) were increased for the duration of hypoxia. Cerebral blood flow (radiolabelled microspheres) increased transiently for 48 h from 65.9 (±4.4) to 100.4 (±9.9) ml · min^-1 · 100 g^-1 with no change in its regional distribution. Coronary flow was elevated for the duration of hypoxia from 181 (±15) to between 280 (±33) and 350 (±37) ml · min^-1 · 100 g^-1 with a more pronounced increment in right heart flow, and a decline in the endocardial/epicardial flow ratio. These regional flow increases resulted from a sustained decrease in pancreatic flow from 234 (±11) to 125 (±13) ml · min^-1 · 100 g^- for 96 h, with persisting decreases in splenic flow from 249 (±30) to from 787 (±70) to 540 (±31) ml · min^-1 · 100 g^-1, occurring at 48 and 72 h, respectively. Therefore, there is a redistribution of cardiac output during 96 hours of hypoxia with increased flows to heart and brain, and decreased flows to abdominal viscera.