Regional circulatory responses to 96 hours of hypoxia in conscious sheep.
Exposure of adult ewes to normobaric hypoxia (PaO2 40 mm Hg) for 96 h led to increases of VE (+ 54%), while VO2 decreased by 48%. PaCO2 declined progressively to stabilize at 24 (+/- 1.5 SE) mm Hg by 24-48 h. Cardiac output (thermodilution) was elevated 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 X min-1 X 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 X min-1 X 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 X min-1 X 100 g-1 for 96 h, with persisting decreases in splenic flow from 249 (+/- 30) to 100 (+/- 18), and in renal cortical flow from 787 (+/- 70) to 540 (+/- 31) ml X min-1 X 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.
D000818:Animals; D001775:Blood Circulation; D001921:Brain / Q000098:blood supply; D003243:Consciousness; D003326:Coronary Circulation; D005260:Female; D006439:Hemodynamics; D000860:Hypoxia / Q000503:physiopathology*; D012039:Regional Blood Flow; D012119:Respiration; D012756:Sheep