Cerebral blood flow adaptations following 90 days head-down bed rest: Evidence from pseudo-continuous arterial spin labeling magnetic resonance imaging

Prolonged microgravity exposure disrupts cerebral hemodynamic homeostasis, yet longitudinal cerebral blood flow (CBF) adaptation remains poorly understood. This study investigated CBF changes under 90 days head-down bed rest (HDBR) in 36 healthy adults using pseudo-continuous arterial spin labeling (pCASL) MRI. Analyses included region-of-interest (global/regional CBF) and voxel-based whole-brain assessments, alongside physiological correlations. Results demonstrated stable global CBF after HDBR but revealed distinct microcirculatory redistribution: the vertebrobasilar (VB) territory exhibited significant perfusion increases, while voxel-based analysis identified elevated CBF in the left fusiform gyrus and reduced perfusion in the right superior frontal gyrus, middle cingulate gyrus, and Heschl's gyrus. Physiological correlations indicated negative associations between VB-CBF and diastolic blood pressure (DBP)/mean arterial pressure (MAP), with pre-HDBR heart rate as a key modulator of VB perfusion changes. A potential relationship between age and altered CBF has been found in the right superior frontal gyrus in young adults. These findings suggest that although global CBF stabilizes during simulated microgravity, posterior circulation-dominated microvascular redistribution occurs, tightly coupled with cardiovascular dynamics, offering critical insights for optimizing countermeasures in spaceflight and terrestrial cerebrovascular diseases.