How hypertension damages your health

 | January 1, 2007

How hypertension damages your health

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 5) — those most likely to be affected by the disease.

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.

African Americans are particularly at risk: Not only are they more likely to develop hypertension, but they are also more apt to suffer from its complications. African Americans with hypertension have higher rates of stroke, heart disease, kidney disease, and diabetes compared with whites with hypertension. African Americans are also more likely to die as a result of hypertension than whites are.

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Stroke

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.

More than 80% 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.

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.

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Coronary artery disease

By making your blood vessel walls more susceptible to atherosclerosis, hypertension increases not only your likelihood of having a stroke, but also your risk of heart attack. When coronary arteries become completely blocked by a clump of platelets or by debris such as fats, cholesterol, and dead cells, a heart attack results.

Fragments from these deposits, called emboli, can also break away from large blood vessels such as the aorta, travel through the bloodstream, and eventually block other vessels, such as those supplying the legs (causing circulatory problems) or the brain (causing stroke). Having high cholesterol in addition to hypertension only exacerbates this process and increases your risk of cardiovascular complications.

In addition to making atherosclerosis more likely, hypertension also forces the heart to work increasingly harder to drive blood through the body. As a result, the left ventricle, the heart's main pumping chamber, becomes thicker and more muscular in order to contract with greater force. This compensation — known as left ventricular hypertrophy (LVH) — eventually becomes counterproductive. As the heart muscle enlarges, it needs progressively more oxygen, but the arteries, which are also thickened and narrowed as a result of hypertension, become less able to deliver it. The lack of oxygen can cause angina (chest pain) and, if severe enough, a heart attack.

The combination of LVH and diseased coronary arteries — spurred on by hypertension — may also lead to congestive heart failure (the inability of your heart to pump blood efficiently throughout your body). In fact, if you have uncontrolled high blood pressure, you're twice as likely to develop heart failure as someone without hypertension.

Unlike your biceps, the thickness of your heart muscle doesn't translate into strength. With LVH, your heart muscle thickens, but your blood supply usually can't swell to the same degree, especially if your arteries are damaged. Without an adequate supply of blood, your heart weakens, and this in turn can lead to either of the two primary kinds of congestive heart failure — systolic or diastolic. Systolic heart failure arises when your heart cannot pump forcefully enough to push a sufficient amount of blood into circulation. Diastolic heart failure occurs when your heart can't properly fill with blood because it's stiff and has trouble relaxing.

Symptoms of heart failure include weakness and fatigue (because your muscles aren't getting enough blood), shortness of breath, and the accumulation of fluid in your lungs, feet, ankles, and legs (known as edema).

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Dementia

By accelerating atherosclerosis, hypertension can contribute to dementia. Atherosclerosis interferes with circulation, and a lack of blood supply can produce areas of dead tissue in the brain called small infarcts. Multi-infarct dementia, a well-recognized cause of memory loss in older people, is caused by a series of these tiny strokes. Each one affects such a small area of the brain that symptoms may not be apparent until a substantial amount of tissue has been destroyed.

The link between multi-infarct dementia and hypertension escaped attention for many years because people suffering from dementia often have normal or low blood pressure. But long-term studies now show that blood pressure in midlife may predict brain function years later. One example is the Honolulu-Asia Aging Study, which began in the mid-1960s and evaluated the health of Japanese American men over nearly three decades. The participants' average age was 53 at the beginning of the study and 78 at final evaluation. When the researchers compared performance on cognitive function tests and midlife blood pressure, they found a link between poor mental function late in life and high systolic pressure 25 years earlier. There was no link between mental function and diastolic pressure, a finding that underscores the importance of treating isolated systolic hypertension.

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Kidney disease

The kidneys play a crucial role in the body's natural control of blood pressure by regulating the amount of water and sodium in circulation. When blood pressure rises, the kidneys excrete water and sodium. This action helps bring pressure back down by stimulating the loss of body fluids (through urination, for example), thereby reducing the volume of circulating blood. When blood pressure falls, the kidneys retain water and sodium to conserve blood volume and raise pressure.

Sustained high blood pressure damages the structures in the kidneys, called glomeruli, which filter waste products, sodium, and water from the bloodstream. Glomerular destruction due to hypertension is one of the most common causes of renal failure (loss of kidney function). People with renal failure become bloated with excessive fluid and weakened by the accumulation of toxic chemicals normally excreted by the kidneys. Uncontrolled hypertension is second only to diabetes as a cause of renal failure, accounting for about one in four new cases.

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Eye damage

The eye works by focusing visual images onto the retina, a sheet of nerve tissue at the back of the eyeball. Immediately behind the retina lies a network of tiny blood vessels that keeps this tissue richly supplied with oxygen and nutrients. Hypertension can cause these arteries to narrow or break and bleed into the retina. It can also lead to swelling of the optic nerve, which carries images to the brain. In patients with longstanding, untreated hypertension, the result can be impaired vision and even blindness.

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Review Date: 2007-01-01

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