Cerebral and spinal cord blood flow dynamics during high sustained +Gz.

This study had two purposes. First, the use of Transonic flowprobes placed on the common carotid and internal carotid arteries of seven male baboons was evaluated for measuring cerebral blood flow (BF) during +Gz stress. The approach was to compare BF's obtained with these flowprobes to microsphere measurements of total cerebral BF. The second purpose was to measure regional variations in cerebral and spinal cord BF during +Gz to test the hypothesis that +Gz produces a differential perfusion deficit throughout the central nervous system so that BF's at the superior portion of the brain are decreased more than in areas of the brain that are nearer to the heart. The results indicate that internal carotid artery and microsphere measurements of total brain BF were related so that the relative decrease in internal carotid artery BF was consistently comparable to that measured with the labeled microsphere technique. Thus, Transonic flowprobes placed on the internal carotid artery of the baboon give reliable estimates of cerebral BF during +Gz stress. The microsphere BF data demonstrated that there were no regional differences in the relative decrease in BF measured in the brain or spinal cord during +Gz. We conclude that our results do not support the hypothesis of a gradient of BF deficit within the brain or spinal cord during +Gz.