Site-specific Cerebral Vasomotion In The Posterior Cerebral Arteries

Blood flow in the vertebral artery (VA), the upstream of posterior cerebral blood flow (CBF), may display distinct responses compared to transcranial Doppler (TCD) data measuring blood velocity in the posterior cerebral artery (PCA) as an indicator of posterior CBF. PURPOSE: This study aimed to investigate whether changes in PCA blood flow correspond to alterations in the upstream blood flow of PCA (VA) or if the PCA blood flow demonstrates specific responses to physiological conditions within the posterior circulation. METHODS: To test this aim, a 3 Tesla (SIGNA, GE MEDICAL SYSTEMS) time-resolved phase-contrast MRI employing three-directional flow velocity encoding, referred to as 4D flow MRI was utilized to assess CBF in 24 subjects during supine baseline, and lower body negative pressure (LBNP). Segmentation, artery contouring, velocity, area, and flow measurements were conducted using CVI42 software and 4D FLOW module (v5.16-2022, Circle Vascular Imaging) for 11 flow measurement sites per subject. RESULTS: In the anterior cerebral circulation, alterations in the CBF of the upstream artery (internal carotid artery) mirrored those of the downstream arteries (middle and anterior cerebral arteries) from baseline to LBNP. However, in the posterior cerebral circulation, the CBF of the upstream artery (basilar and vertebral arteries) did not correlate with the CBF of the downstream artery (PCA). CONCLUSION: Remarkably, the upstream posterior CBF decreased during LBNP, while the downstream PCA blood flow remained robust. These observations imply that even under mild physiological conditions, such as orthostatic stress, the downstream cerebral vasculature demonstrates site-specific regulation, leading to distinct blood distribution within the posterior cerebral circulation. Supported by JSPS KAKENHI #22H03470, CNES #4800001180, Normandy Council, and the ERDF-ESF operational program. JSPS KAKENHI #22H03470, CNES #4800001180, Normandy Council, and the ERDF-ESF operational program