“How does high blood pressure cause a stroke?”

There are two main types of stroke. One is an ischemic due to a blood clot either forming in a vessel supplying the brain with oxygen or a blood clot that travels to the vessel and blocks it depriving the part of the brain supplied by the vessel of oxygen.
Less commonly a piece of cholesterol may break off and travel to the brain. These strokes are called thrombotic or embolic respectively. Thrombotic strokes are almost always due to partial blockages in the artery that are caused by cholesterol build up and hypertension. The arterial wall is damaged and a blood clot forms.

The other main type of stroke is hemorrhagic. The arterial wall is damaged by longstanding hypertension and finally bursts. Bleeding in the brain is a serious problem because the brain is in an enclosed space, the skull, and pressure builds up rapidly causing even more damage. Occasionally there may be a small aneurysm in the brain that ruptures due to high pressure.

The high BP puts more stress on the carotid and other arteries going to the brain. This can accelerate the development of blockages (plaque), which can fly off and cause a stroke. If the BP is very high, sometimes the arteries in the brain can burst, causing a cerebral hemorrhage type of stroke, but this is rare. 

Regards,

Gerald Lewis, MD