New Insights Into Cerebrovascular Pathophysiology and Hypertension

Abstract

Despite advances in acute management and prevention of cerebrovascular disease, stroke and vascular cognitive impairment together remain the world's leading cause of death and neurological disability. Hypertension and its consequences are associated with over 50% of ischemic and 70% of hemorrhagic strokes but despite good control of blood pressure (BP), there remains a 10% risk of recurrent cerebrovascular events, and there is no proven strategy to prevent vascular cognitive impairment. Hypertension evolves over the lifespan, from predominant sympathetically driven hypertension with elevated mean BP in early and mid-life to a late-life phenotype of increasing systolic and falling diastolic pressures, associated with increased arterial stiffness and aortic pulsatility. This pattern may partially explain both the increasing incidence of stroke in younger adults as well as late-onset, chronic cerebrovascular injury associated with concurrent systolic hypertension and historic mid-life diastolic hypertension. With increasing arterial stiffness and autonomic dysfunction, BP variability increases, independently predicting the risk of ischemic and intracerebral hemorrhage, and is potentially modifiable beyond control of mean BP. However, the interaction between hypertension and control of cerebral blood flow remains poorly understood. Cerebral small vessel disease is associated with increased pulsatility in large cerebral vessels and reduced reactivity to carbon dioxide, both of which are being targeted in early phase clinical trials. Cerebral arterial pulsatility is mainly dependent upon increased transmission of aortic pulsatility via stiff vessels to the brain, while cerebrovascular reactivity reflects endothelial dysfunction. In contrast, although cerebral autoregulation is critical to adapt cerebral tone to BP fluctuations to maintain cerebral blood flow, its role as a modifiable risk factor for cerebrovascular disease is uncertain. New insights into hypertension-associated cerebrovascular pathophysiology may provide key targets to prevent chronic cerebrovascular disease, acute events, and vascular cognitive impairment.

Keywords: blood pressure; hemorrhage; hypertension; pathology; stroke; vascular stiffness.

Figure 1. Radiological manifestations of small vessel disease.

A) An acute small subcortical infarct on DWI imaging; B) Deep and periventricular white matter hyperintensities (arrowed); C) Dilated perivascular spaces bilaterally in the basal ganglia (arrowed on the left); D) a slit-like haemosiderin-lined cavity due to a chronic right intracerebral haemorrhage, subcortical (deep) cerebral microbleeds (white arrow) and a cortical (lobar) (black arrow) microbleed.

Figure 2. Relationship between ‘Usual’ diastolic and systolic blood pressure and white matter hyperintensities in the UK Biobank Study, stratified by age group.

Severity of white matter hyperintensities is expressed as the ratio of their volume to the average volume in the youngest patients with the lowest blood pressure, plotted on a logarithmic scale. Wartolowska K, Webb AJS. EHJ (2020).

Figure 3. Rate of progression of aortic pulse wave velocity (PWV) and middle cerebral pulsatility (PI) over 5 years in 188 patients after TIA or minor stroke, stratified by quartiles of age.

Individual changes are show, with summary results derived from a mixed effect linear model, stratified by quartiles of age and subdivided into men (red) and women (blue).

Figure 4. Major mechanisms of cerebrovascular adaptation to changes in blood pressure and demand for blood flow to control cerebral perfusion.