Age, hypertension, diabetes, and smoking all cause damage within the microvasculature. These damaged vessels may leak protein that deposits in the walls, producing stiffness and hardening. Microvascular damage makes it difficult for the vessels to dilate and constrict. When flow through these small vessels is sufficiently diminished, a small (lacunar) stroke or silent stroke may result. Risk factor modification is the key to preventing microvascular disease and subsequent stroke. Microvascular disease of the brain affects half of all people aged 70 or older, according to large MR studies that have been done. These areas of MR signal abnormality may be due to demyelina-tion or ischemic damage, and the demyelinating lesions are thought to have an ischemic basis as well (i.e., ischemic demyelination). Microvascular disease of the brain also relates in part to impaired blood flow during periods of relative hypotension, which leads to ischemia in brain areas with disturbed autoregulation. Stroke leads to a breakdown in cerebral autoregulation within the ischemic zone, and vascular damage from hypertension, amyloid angiopathy, atherosclerosis, and other disorders may compromise cerebral autoregulation as well. Research is under way to determine the ischemic threshold in a clinically useful way so that hypotensive ischemia within compromised vascular territories might be avoided. Currently, there is no way to know when blood pressure has been lowered sufficiently to compromise susceptible vascular territories.
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