CEREBRAL AND SPINAL-CORD BLOOD-FLOW DYNAMICS DURING HIGH SUSTAINED +GZ

This study had two purposes. First, the use of Transonic flowprobes pl aced 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 flowpr obes to microsphere measurements of total cerebral BF. The second purp ose was to measure regional variations in cerebral and spinal cord BF during +Gz to test the hypothesis that +Gz produces a differential per fusion deficit throughout the central nervous system so that BF's at t he superior portion of the brain are decreased more than in areas of t he brain that are nearer to the heart. The results indicate that inter nal carotid artery and microsphere measurements of total brain BF were related so that the relative decrease in internal carotid artery BF w as consistently comparable to that measured with the labeled microsphe re technique. Thus, Transonic flowprobes placed on the internal caroti d artery of the baboon give reliable estimates of cerebral BF during Gz stress. The microsphere BF data demonstrated that there were no reg ional differences in the relative decrease in BF measured in the brain or spinal cord during +Gz. We conclude that our results do not suppor t the hypothesis of a gradient of BF deficit within the brain or spina l cord during +Gz.