Regional distribution of cardiac output in unanesthetized baboons during +Gz stress with and without an anti-G suit

Abstract

The radiolabeled (46Sc, 85Sr, 141Ce, and 125I) microsphere (15 mu diameter) technique was used to measure blood flow to most major organs of eight chronically instrumented, unanesthetized baboons during exposure to +5 Gz and +7 Gz stress. Exposure to +5 Gz with anti-G suit support resulted in tachycardia, increased total peripheral resistance, increased aortic pressure, decreased aortic flow velocity, decreased blood flow to visceral beds, and no change in cerebral or coronary blood flows. Exposure to +7 Gz with anti-G suit support, in most animals, caused tachycardia, small increases in coronary blood flow, increased arterial pressure, decreased aortic flow velocity, and decreased blood flow to the retina, kidney, liver, spleen, pancreas, and no change in cerebral blood flow. When the animals were exposed to +Gz without anti-G suit inflation, the reductions in aortic flow velocity were more dramatic and heart-level arterial pressure was decreased below baseline values. Coronary blood flow was still increased during +Gz without anti-G suit support. Brain blood flow decreased and the regional blood flows throughout the body were decreased further than during similar +Gz exposures with a G suit. These results indicate that the baboon compensates for the +Gz-induced decrease in cardiac output by a redistribution of blood flow away from the renal and splanchnic beds in an apparent effort to maintain blood flow to the brain and heart.