Cerebral blood flow

Cerebral blood flow (CBF) is the volume of blood delivered per unit time, expressed in mL per 100 g per minute, regulated via autoregulation, arterial CO₂ sensitivity, and neurovascular coupling. In neurovascular coupling, neuronal activity triggers vasoactive agent release from neurons and astrocytes — nitric oxide, prostaglandins, potassium — relaxing arteriolar smooth muscle and capillary pericytes to raise perfusion at sites of metabolic demand. Resting CBF declines roughly 5% per decade, driven by rising cerebrovascular resistance, arterial stiffening, and impaired endothelial NO synthesis; pulsatility increases after midlife and correlates with white matter hyperintensity burden (Tarumi and Zhang, 2017). Chronic hypoperfusion reduces oxygen and glucose delivery, promotes capillary stalling, and reinforces amyloid-β accumulation — impaired clearance worsens vascular dysfunction, which deepens hypoperfusion, a bidirectional cycle in Alzheimer and vascular dementia (Toth et al., 2017). In a one-year RCT (n = 56 older adults), aerobic training raised CBF 5 ± 7% versus 0 ± 5% in controls (p = 0.007), reduced cerebrovascular resistance 7%, and correlated with improved recall (r = −0.49; Tomoto et al., 2023). A 2022 systematic review found consistent associations between exercise-induced CBF gains and cognition, though protocol heterogeneity limits effect estimates (Renke et al., 2022). Methods include arterial spin labelling MRI, transcranial Doppler, and phase-contrast MRI. Whether hypoperfusion causally precedes dementia or co-occurs with it remains unresolved.