Absolute changes in regional cerebral blood flow in association with upright posture in humans: An orthostatic PET study

To determine whether hemodynamic parameters are changed by upright posture in healthy middle-aged humans, absolute values of regional cerebral blood f low (rCBF) were investigated for three different orthostatic conditions. Me thods: PET with [O-15]H2O and arterial blood sampling were performed on eig ht middle-aged healthy volunteers while they were sitting passively or stan ding actively. Absolute rCBF values estimated by the autoradiographic metho d in regions of interest were compared using ANOVA, and relative changes in rCBF were also analyzed voxel by voxel using statistical parametric mappin g (SPM). Results: Physiologic data remained unchanged for different conditi ons. ANOVA and SPM showed that absolute and relative rCBF levels were signi ficantly elevated in the cerebellar vermis in the standing position compare d with those in the supine and sitting positions. In contrast, ANOVA showed that rCBF in the frontal and parietal cortices tended to be lower in the s itting and standing positions than in the supine position. Regression analy sis showed that the frontal rCBF measured during standing tended to be inve rsely correlated with age. Conclusion: The results showed that cerebellar v ermis activation was more marked in the standing position than in the sitti ng or supine positions, indicating that the vermis is a neural substrate fo r controlling voluntary upright posture. Brain perfusion in the distal inte rnal carotid artery region may be subject to orthostatic postural changes i n healthy middle-aged humans.