What is high blood pressure?

High blood pressure (HBP) or hypertension means high pressure (tension) in the arteries. Arteries are vessels that carry blood from the pumping heart to all the tissues and organs of the body. High blood pressure does not mean excessive emotional tension, although emotional tension and stress can temporarily increase blood pressure. Normal blood pressure is below 120/80; blood pressure between 120/80 and 139/89 is called "pre-hypertension", and a blood pressure of 140/90 or above is considered high.

The top number, the systolic blood pressure, corresponds to the pressure in the arteries as the heart contracts and pumps blood forward into the arteries. The bottom number, the diastolic pressure, represents the pressure in the arteries as the heart relaxes after the contraction. The diastolic pressure reflects the lowest pressure to which the arteries are exposed.

An elevation of the systolic and/or diastolic blood pressure increases the risk of developing heart (cardiac) disease, kidney disease, hardening of the arteries (atherosclerosis or arteriosclerosis), eye damage, and stroke (brain damage). These complications of hypertension are often referred to as end-organ damage because damage to these organs is the end result of chronic (long duration) high blood pressure. For that reason, the diagnosis of high blood pressure is important so efforts can be made to normalize blood pressure and prevent complications.

It was previously thought that rises in diastolic blood pressure were a more important risk factor than systolic elevations, but it is now known that in people 50 years or older systolic hypertension represents a greater risk.

The American Heart Association estimates high blood pressure affects approximately one in three adults in the United States - 73 million people. High blood pressure is also estimated to affect about two million American teens and children, and the Journal of the American Medical Association reports that many are under-diagnosed. Hypertension is clearly a major public health problem.

How is the blood pressure measured?

The blood pressure usually is measured with a small, portable instrument called a blood pressure cuff (sphygmomanometer). (Sphygmo is Greek for pulse, and a manometer measures pressure.) The blood pressure cuff consists of an air pump, a pressure gauge, and a rubber cuff. The instrument measures the blood pressure in units called millimeters of mercury (mm Hg).

The cuff is placed around the upper arm and inflated with an air pump to a pressure that blocks the flow of blood in the main artery (brachial artery) that travels through the arm. The arm is then extended at the side of the body at the level of the heart, and the pressure of the cuff on the arm and artery is gradually released. As the pressure in the cuff decreases, a health practitioner listens with a stethoscope over the artery at the front of the elbow. The pressure at which the practitioner first hears a pulsation from the artery is the systolic pressure (the top number). As the cuff pressure decreases further, the pressure at which the pulsation finally stops is the diastolic pressure (the bottom number).

Blood pressure can be affected by several factors, so it is important to standardize the environment when blood pressure is measured. For at least one hour before blood pressure is taken, avoid eating, strenuous exercise (which can lower blood pressure), smoking, and caffeine intake. Other stresses may alter the blood pressure and need to be considered when blood pressure is measured.

Even though most insurance companies consider high blood pressure to be 140/90 and higher for the general population, these levels may not be appropriate cut-offs for all individuals. Many experts in the field of hypertension view blood pressure levels as a range, from lower levels to higher levels. Such a range implies there are no clear or precise cut-off values to separate normal blood pressure from high blood pressure. Individuals with so-called pre-hypertension (defined as a blood pressure between 120/80 and 139/89) may benefit from lowering of blood pressure by life style modification and possibly medication especially if there are other risk factors for end-organ damage such as diabetes or kidney disease (life style changes are discussed below).

For some people, blood pressure readings lower than 140/90 may be a more appropriate normal cut-off level. For example, in certain situations, such as in patients with long duration (chronic) kidney diseases that spill (lose) protein into the urine (proteinuria), the blood pressure is ideally kept at 130/80, or even lower. The purpose of reducing the blood pressure to this level in these patients is to slow the progression of kidney damage. Patients with diabetes (diabetes mellitus) may also benefit from blood pressure that is maintained at a level lower than 130/80. In addition, African Americans, who have an increased risk for developing the complications of hypertension, may decrease this risk by reducing their systolic blood pressure to less than 135 and the diastolic blood pressure to 80 mm Hg or less.

In line with the thinking that the risk of end-organ damage from high blood pressure represents a continuum, statistical analysis reveals that beginning at a blood pressure of 115/75 the risk of cardiovascular disease doubles with each increase in blood pressure of 20/10. This type of analysis has led to an ongoing "rethinking" in regard to who should be treated for hypertension, and what the goals of treatment should be.

Isolated systolic high blood pressure

Remember that the systolic blood pressure is the top number in the blood pressure reading and represents the pressure in the arteries as the heart contracts and pumps blood into the arteries. A systolic blood pressure that is persistently higher than 140 mm Hg is usually considered elevated, especially when associated with an elevated diastolic pressure (over 90).

Isolated systolic hypertension, however, is defined as a systolic pressure that is above 140 mm Hg with a diastolic pressure that still is below 90. This disorder primarily affects older people and is characterized by an increased (wide) pulse pressure. The pulse pressure is the difference between the systolic and diastolic blood pressures. An elevation of the systolic pressure without an elevation of the diastolic pressure, as in isolated systolic hypertension, therefore, increases the pulse pressure. Stiffening of the arteries contributes to this widening of the pulse pressure.

Once considered to be harmless, a high pulse pressure is now considered an important precursor or indicator of health problems and potential end-organ damage. Isolated systolic hypertension is associated with a two to four times increased future risk of an enlarged heart, a heart attack (myocardial infarction), a stroke (brain damage), and death from heart disease or a stroke. Clinical studies in patients with isolated systolic hypertension have indicated that a reduction in systolic blood pressure by at least 20 mm to a level below 160 mm Hg reduces these increased risks.

White coat high blood pressure

A single elevated blood pressure reading in the doctor's office can be misleading because the elevation may be only temporary. It may be caused by a patient's anxiety related to the stress of the examination and fear that something will be wrong with his or her health. The initial visit to the physician's office is often the cause of an artificially high blood pressure that may disappear with repeated testing after rest and with follow-up visits and blood pressure checks. One out of four people that are thought to have mild hypertension actually may have normal blood pressure when they are outside the physician's office. An increase in blood pressure noted only in the doctor's office is called 'white coat hypertension.' The name suggests that the physician's white coat induces the patient's anxiety and a brief increase in blood pressure. A diagnosis of white coat hypertension might imply that it is not a clinically important or dangerous finding.

However, caution is warranted in assessing white coat hypertension. An elevated blood pressure brought on by the stress and anxiety of a visit to the doctor may not necessarily always be a harmless finding since other stresses in a patient's life may also cause elevations in the blood pressure that are not ordinarily being measured. Monitoring blood pressure at home by blood pressure cuff or continuous monitoring equipment or at a pharmacy can help estimate the frequency and consistency of higher blood pressure readings. Additionally, conducting appropriate tests to search for any complications of hypertension can help evaluate the significance of variable blood pressure readings.

Borderline high blood pressure

Borderline hypertension is defined as mildly elevated blood pressure higher than 140/90 mm Hg at some times, and lower than that at other times. As in the case of white coat hypertension, patients with borderline hypertension need to have their blood pressure taken on several occasions and their end-organ damage assessed in order to establish whether their hypertension is significant.

People with borderline hypertension may have a tendency as they get older to develop more sustained or higher elevations of blood pressure. They have a modestly increased risk of developing heart-related (cardiovascular) disease. Therefore, even if the hypertension does not appear to be significant initially, people with borderline hypertension should have continuing follow-up of their blood pressure and monitoring for the complications of hypertension.

If, during the follow-up of a patient with borderline hypertension, the blood pressure becomes persistently higher than 140/ 90 mm Hg, an anti-hypertensive medication is usually started. Even if the diastolic pressure remains at a borderline level (usually under 90 mm Hg, yet persistently above 85) treatment may be started in certain circumstances.

Blood pressure persistently higher than 140/ 90 mm Hg usually is treated with lifestyle modifications and medication. More aggressive treatment may be recommended in certain circumstances if the diastolic pressure remains at a borderline level (usually less than 90 mm Hg, yet persistently above 85). These circumstances include borderline diastolic pressures in association with end–organ damage, systolic hypertension, or factors that increase the risk of cardiovascular disease, such as age over 65 years, African American decent, smoking, hyperlipemia (elevated blood fats), or diabetes.

Any one of the several classes of medications may be started, except the alpha-blocker medications. The alpha-blockers are used only in combination with another anti-hypertensive medication in specific medical situations. (See the next section for a more detailed discussion of each of the several classes of anti-hypertensive medications.)

In some situations, certain classes of anti–hypertensive drugs are preferable to others as the first line (preferred first choice) drugs. Angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blocking (ARB) drugs are the drugs of choice in patients with heart failure, chronic kidney failure (in diabetics or non–diabetics), or heart attack (myocardial infarction) that weakens the heart muscle (systolic dysfunction). Also, beat-blockers are sometimes the preferred treatment in hypertensive patients with a resting tachycardia (racing heart beat when resting) or an acute (rapid onset, current) heart attack.

Patients with hypertension may sometimes have a co–existing, second medical condition. In such cases, a particular class of anti–hypertensive medication or combination of drugs may be chosen as the first line approach. The idea in these cases is to control the hypertension while also benefiting the second condition. For example, beta–blockers may treat chronic anxiety or migraine headache as well as hypertension. Also, the combination of an ACE inhibitor and an ARB drug can be used to treat certain diseases of the heart muscle (cardiomyopathies) and certain kidney diseases where reduction in proteinuria would be beneficial.

In other situations, certain classes of anti–hypertensive medications should not be used (are contraindicated). Dihydropyridine calcuium channel blockers used alone may cause problems for patients with chronic renal disease by increasing proteinuria. However, an ACE inhibitor will blunt this effect. The non–dihydropyridine type of calcium channel blockers should not be used in patients with heart failure. However, these drugs may be beneficial in treating certain arrhythmias. Some drugs, such as minoxidil, since it is so powerful, usually are relegated to second or third line choices for treatment. Clonidine is an excellent drug but has side effects such as fatigue, sleepiness, and dry month making it a second or third line choice. See the section below on pregnancy for the anti–hypertensive drugs that are appropriate or inappropriate for use in pregnant women.