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WHAT IS HYPERTENSION? ? Hypertension is a medical term for high blood pressure. Blood pressure refers to the pressure exerted by circulating blood on the inner walls of the arteries that carry blood from the heart. It is measured based upon two values for arterial pressure: the systolic pressure as the heart contracts and the diastolic pressure as it relaxes between beats.

Blood pressure varies naturally over a person's lifetime (normally increasing with age) as well as over the course of a day. In addition, activity affects blood pressure, which rises as a normal response to physical exertion and stress. However, patients with hypertension have high blood pressure even at rest. Untreated hypertension puts strain on the heart and arteries, eventually damaging such tissues, and is a key risk factor for heart failure, heart attack (myocardial infarction), and stroke.

The standard classification for high blood pressure suggested by the seventh Jo int National Committee (JNC) on Detection, Evaluation, and Diagnosis of High Blood Pressure is listed below. It is based on the average of two or more blood pressure readings at each of two or more visits after an initial screen.

Stage 1: systolic 140 to 159 mmHg OR diastolic 90 to 99 mmHg
Stage 2: systolic >160 mmHg OR diastolic >100 mmHg

These definitions apply to adults who are not taking medications for hypertension and who are not acutely ill. If the two pressures fall in different categories, the higher one is used to determine the severity of the hypertension.

The term prehypertension was chosen because patients with blood pressures in this range are at increased risk of progressing to hypertension and of developing cardiovascular complications.

Most adults with hypertension have what is called essential or primary hypertension, because the cause is not known. A small subset of adults have secondary hypertension, in which an underlying and potentially correctable cause can be identified.

HOW COMMON IS HYPERTENSION? ? Hypertension is a common health problem. According to a national health survey in the United States, hypertension (systolic >140 mmHg and/or diastolic >90 mmHg) was present in 32 percent of African-Americans and 23 percent of whites and Mexican-Americans.

Hypertension is more common as people grow older. As an example, among people over age 60, it occurs in 65 percent of African-American men, 80 percent of African-American women, 55 percent of white men and 65 percent of white women ( show figure 1 and show figure 2 ).

Unfortunately, even though increasing numbers of people are being diagnosed with hypertension, many people still are not controlling it adequately. According to the same national survey, control of hypertension was achieved by only 25 percent of African-Americans and whites and 14 percent of Mexican-Americans.

DIAGNOSIS OF HYPERTENSION ? The diagnosis of hypertension is made by measurement of the blood pressure, An individual's blood pressure varies with time and some are anxious on a visit to a doctor's office. As a result, an individual should not be labeled as having hypertension unless their blood pressure is persistently high after at least three office visits over several weeks to months. The only exceptions are if the blood pressure is very high or if there is evidence of damage from elevated blood pressure, such as heart, eye, or kidney injury (also called "target organ damage"). During the initial evaluation period before a treatment decision is made, patients should also be encouraged to measure their blood pressure at home or work.

WHY SHOULD HYPERTENSION BE TREATED? ? Untreated hypertension can lead to a variety of vascular complications, such as heart disease and stroke. There is a gradually increasing rate of these two medical conditions as blood pressure rises above 110/75, which is still in the healthy range. ( See "Patient information: Therapy for essential hypertension" ).

A summary of the results of 17 studies of mild to moderate hypertension in adults under age 65 shows the benefits of treatment. Compared to people who did not receive treatment, there was a significant reduction in the number of coronary events and stroke among those who were given blood pressure lowering medications for four to five years.

A report from the Framingham Heart Study also confirmed the benefit of long-term treatment for hypertension on the number of cases of heart disease and deaths. In patients aged 50 to 59, deaths from all causes as well as from heart disease were significantly reduced when the number of patients being treated doubled. Equal if not greater benefits have been shown for the treatment of people with hypertension who are over age 65.

WHO SHOULD BE GIVEN WHAT TREATMENT? ? Treatment of hypertension usually begins with nondrug strategies. These include moderate restriction on salt in the diet, weight reduction in those who are overweight, avoidance of excess alcohol intake, and regular aerobic exercise ( show table 1 ). Making these lifestyle changes involves little or no risk, and is also recommended by the JNC for patients with prehypertension who are also at increased risk compared to those with normal blood pressure. ( See "Patient information: Hypertension and diet and weight" ).

Treatment with antihypertensive medications may be expensive and is often associated with side effects. Thus, there should be clear evidence of likely benefit before medications are used.

The following tables show how the Joint National Committee has divided people with high blood pressure into several different groups according to their risk factors, evidence of target organ damage, and blood pressure levels ( show table 2 and show table 3 ).

The indication for antihypertensive drug therapy in most patients is a blood pressure that is persistently 140/90 mmHg or higher. On the other hand, drug treatment is warranted in patients with diabetes or chronic renal failure who have a blood pressure that is greater than 130/80 mmHg. Certain antihypertensive drugs are used in patients with other conditions, such as heart failure or a heart attack, independent of the need to lower the blood pressure.

The choice of antihypertensive drugs is discussed elsewhere. ( See "Patient information: Therapy for essential hypertension" ).

WHERE TO GET MORE INFORMATION ? Your doctor is the best resource for finding out important information related to your particular case. Not all patients with hypertension are alike, and it is important that your situation is evaluated by someone who knows you as a whole person.