Functional Transcranial Doppler in Stroke Risk

Brain's high metabolic demand requires that cerebral blood vessels have a fine tune regulation of vascular resistance, controlling blood flow distribution. Two fast regulating principles of cerebral perfusion are well accepted: cerebral autoregulation maintains a stable cerebral blood flow for a wide range of systemic blood pressure variation, and cerebral neurovascular coupling adapts local cerebral blood flow to the metabolic needs and activity of the underlying cortex. Transcranial Doppler (TCD) allows a continuous and non-invasive monitoring of cerebral blood flow velocities in the basal cerebral arteries, which change according to distal arterioles vasomotor variations. Functional TCD is a tool designed to measure the increase of local cerebral blood flow due to regional cortical neuronal activation, accomplished by the neurovascular coupling. As endothelial dysfunction affects neurovascular coupling, it disturbs the dynamics of the evoked blood flow response to cortical activation, as assessed by functional TCD. Vascular risk factors, including age, diabetes and smoking habits, have been shown to interfere with neurovascular coupling. Functional TCD can also be useful for evaluating presymptomatic and even prelesional subjects with genetic diseases afecting the endothelial function. Fabry disease patients, without prior history of stroke or transient ischemic attack, had disturbed neurovascular coupling in the visual cortex. Interesting findings seem to show that cerebral blood flow regulation may reflect the neurological dysfunction caused by cerebral microvascular disease, namely associated with slow gait speed and risk of falls. A better understanding of the relationship between cerebral hemodynamics and structural changes in the aging brain is an essential step towards identifying preventive and therapeutic strategies for age related cerebrovascular disease.