Hypertension operates with great stealth. Although it seldom produces symptoms, the intense pounding of blood gradually damages the artery walls. Small arteries are especially vulnerable. The walls respond by thickening and losing their elasticity and strength. As a result, less blood can pass through them, depriving surrounding tissues of oxygen and nutrients. The vessel walls are also more prone to rupture. Eventually, hypertension damages not just the blood vessels themselves, but also the heart, brain, kidneys, and eyes. These are the “target organs” of hypertension (see Figure 1).
The longer you have hypertension, the greater your chances of developing target-organ damage and, consequently, major diseases such as heart disease, stroke, kidney disease, and eye damage.
Figure 1. Danger Zones
Untreated hypertension is the leading cause of stroke, which is the third leading killer in the United States. Two-thirds of people having a first stroke have blood pressures that are higher than 160/95 mm Hg.
An analysis of nine studies, involving a total of more than 420,000 participants, found that the people with the highest diastolic blood pressure (105 mm Hg) were 10 times more likely to have a stroke than those with the lowest diastolic pressure (76 mm Hg). If you have a blood pressure of 160/95 mm Hg, you’re about four times more likely to have a stroke than someone with normal blood pressure.
Hypertension can lead to either of the two types of stroke: ischemic stroke, which is caused by a blockage of a brain artery, and hemorrhagic stroke, which occurs when a vessel in or near the brain ruptures.
Scars blood vessels
About 88% of strokes are ischemic in origin, and atherosclerosis plays an important role in most of these cases. Atherosclerosis is the thickening of the inner layer of artery walls from the buildup of debris — such as fats, cholesterol, and dead cells — from the bloodstream. This buildup narrows the passageway, diminishing or obstructing blood flow (see Figure 6). A stroke occurs when blood supply to part of the brain becomes cut off by either a clot that has developed on the walls of a brain artery (thrombosis) or a clot that has been swept into the brain artery from somewhere else in the body (embolism).
Hypertension is one cause of the initial damage that leads to atherosclerosis. Increased blood pressure damages the vessel walls, causing inflammation. This inflammation, in turn, encourages plaque buildup and narrowing of the arteries. In addition, Framingham Heart Study researchers found an association between high blood pressure and substances that make blood “sticky” and more apt to form stroke-causing clots.
Weakens vessel walls
In hemorrhagic stroke, the walls of small arteries become weakened and eventually burst, causing blood to leak into a portion of the brain, ultimately damaging or destroying it. Because hypertension is the most frequent cause of weakened vessel walls, hemorrhagic stroke is most likely to occur in people with high blood pressure. Although every stroke is dangerous, hemorrhagic events are often the most devastating.
A stroke’s severity depends on which part of the brain is affected and how large the damaged area is. A mild stroke may cause few or no lasting problems. But approximately one-third of major strokes are fatal, and another third cause permanent damage, such as weakness or paralysis on one side of the body, vision disturbances, impaired speech, and diminished intellect.
Figure 2. How Plaque Buildup Narrows the Arteries
High blood pressure can lead to inflammation of the walls of your arteries, which in turn encourages fat to accumulate. This accumulation of fat is known as plaque. As this debris is deposited on artery walls, your arteries become narrower and blood flow is reduced. This thickening of artery walls is known as atherosclerosis.