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Because it was, at one time, measured with a device using a column of mercury, blood pressure measurements are expressed in millimeters of mercury, or mm Hg.

High blood pressure, also called hypertension, is defined as a systolic blood pressure reading greater than 140 mm Hg or a diastolic blood pressure reading greater than 90 mm Hg.

The systolic blood pressure is the top number of a blood pressure reading. It indicates the peak pressure in the blood vessels, when the heart contracts and circulates blood throughout the body.

The diastolic blood pressure is the bottom number of a blood pressure reading. It indicates the lowest pressure in the blood vessels, between heartbeats when the heart is at rest.

The National Institutes of Health has further defined high blood pressure, in the form of the JNC 7 Guidelines. These categories are for people 18 years and older who do not take medication for high blood pressure and do not have a short-term serious illness.

These categories are as follows.

• Normal blood pressure is a systolic blood pressure of less than 120, and a diastolic pressure of less than 80.
• High-normal blood pressure is a systolic blood pressure of 120-139, and a diastolic pressure of 80 to 89.
• Stage 1 high blood pressure is a systolic blood pressure of 140 to 159, and a diastolic pressure of 90 to 99.
• Stage 2 high blood pressure is a systolic blood pressure of equal to or greater than 160, and a diastolic pressure of equal to or greater than 100.

What is going on in the body?

The heart, blood vessels, brain, and kidneys control blood pressure. Blood pressure is also influenced by the amount of fluid and salt in the body. Certain hormones in the body can affect both blood vessels and body fluids.

The force of the contraction of the heart, the heart rate and the elasticity of the arteries are other factors that affect blood pressure. In most people who have high blood pressure, the cause is unknown. When this is the case, high blood pressure is called primary, or essential, hypertension.

What are the signs and symptoms of the condition?

Often, a person will have high blood pressure without any symptoms.

• chest pain
• dizziness
• headaches
• shortness of breath
• visual impairments, such as blurred vision

Either the systolic, or the diastolic, or both blood pressure readings can be elevated. Blood pressure tends to rise with stress or exercise. It should return to normal when the person is at rest.

What are the causes and risks of the condition?

Ninety to 95% of the time, high blood pressure is labeled as essential hypertension, meaning that the cause is unknown. The American Heart Association has identified both controllable and noncontrollable risk factors for high blood pressure.

Uncontrollable risk factors for high blood pressure include age, heredity, and race. In men, high blood pressure occurs most often between 35 and 50 years of age, whereas in women, it generally starts after menopause.

An individual is more likely to develop high blood pressure if his or her parents or close relatives have it. Certain races have a higher incidence of high blood pressure. For example, African Americans develop high blood pressure earlier and more often than Caucasians.

Controllable risk factors for high blood pressure include the following:

• diet high in sodium
• excess or frequent consumption of alcohol
• lack of exercise
• obesity
• smoking
• stress that is not well-managed

Secondary high blood pressure is caused by one or more other medical conditions, such as the following:

• acute lead poisoning
• alcohol abuse
• cocaine and other illegal drugs
• congenital heart disease, such as coarctation of the aorta
• hormonal abnormalities, such as a hyperactive condition of the adrenal glands known as Cushing's syndrome
• injury or radiation therapy to the kidneys
• kidney disease, such as glomerulonephritis and polycystic kidney disease
• medications, such as corticosteroids
• oral contraceptives, or birth control pills
• pregnancy with preeclampsia
• tumors of the adrenal gland, such as a pheochromocytoma

What can be done to prevent the condition?

The American Heart Association guidelines to reduce high blood pressure include:

• for those who smoke, quitting smoking
• moderate sodium intake
• moderation in alcohol intake
• physical activity
• weight control

How is the condition diagnosed?

Adults should have their blood pressure measured at least every two years. The diagnosis of high blood pressure is made on the basis of two or more blood pressure readings. It is diagnosed if two or more readings show a systolic blood pressure greater than 140 or a diastolic blood pressure greater than 90. Other tests may be ordered to look for conditions causing the high blood pressure.

What are the long-term effects of the condition?

Uncontrolled high blood pressure can lead to many serious long-term effects. Damage can occur in the brain, kidneys, and heart. There can also be blood vessel damage to the eye.

High blood pressure can lead to serious health issues, including the following:

• arrhythmias, or irregular heartbeats
• atherosclerosis, which is hardening of the arteries
• chronic kidney failure that requires dialysis or a kidney transplant
• congestive heart failure, in which a weakened heart fails to pump blood effectively
• heart attack
• stroke, or a brain attack

What are the risks to others?

High blood pressure is not contagious and poses no risk to others.

What are the treatments for the condition?

Secondary high blood pressure can sometimes be controlled by treating the underlying condition. Effective treatment of Cushing's syndrome may lower blood pressure. If the high blood pressure is due to coarctation of the aorta, open heart surgery can correct it.

Medications are recommended if the person's blood pressure is greater than 140/90 after 3 months of lifestyle modifications. They are also used if the initial blood pressure is greater than 160/100.

There are many types of medications used to treat high blood pressure. The medications are classified as follows:

• Angiotensin-converting enzyme inhibitors, or ACE inhibitors, block the production of a body chemical that constricts the arteries. ACE inhibitors include benazepril hydrochloride (i.e., Lotensin), enalapril maleate (i.e., Vasotec), and quinapril hydrochloride (i.e., Accupril).
• Angiotensin II receptor blockers block the effect of a body chemical that constricts the arteries and are similar ACE inhibitors. This group of medications includes valsartan (i.e., Diovan), losartin potassium (i.e., Cozaar), and candesartan (i.e., Atacand).
• Beta-blockers reduce blood pressure by lowering the heart rate and decreasing the force of each heartbeat. Common beta-blockers include atenolol (i.e., Tenormin), propranolol hydrochloride (i.e., Inderal, InnoPran), and nadolol (i.e., Corgard).
• Calcium channel blockers are divided into two types. Some calcium channel blockers relax the blood vessels. These include amlodipine besylate (i.e., Norvasc) and nifedipine (i.e., Adalat, Procardia). The calcium channel blockers diltiazem hydrochloride (i.e., Cardizem, Cartia, Dilacor, Diltia, Tiazac) and verapamil (i.e., Calan, Covera, Isoptin, Verelan) work by lowering the heart rate.
• Diuretics, or water pills, help the body get rid of extra fluid and sodium. Common diuretics include furosemide (i.e., Lasix), hydrochlorothiazide (i.e., Esidrix, HydroDIURIL, Microzide, Oretic, HCTZ), and chlorthalidone.
• Sympathetic nerve inhibitors keep the nervous system from constricting arteries. This group includes clonidine hydrochloride (i.e., Catapres), guanabenz acetate (i.e., Wytensin), and alpha methyldopa (i.e., Aldomet).
• Vasodilators relax the muscles in the blood vessel walls and allow the vessels to dilate. Common vasodilators include isosorbide dinitrate (i.e., Dilatrate, Isordil) and hydralazine.

The American Heart Association recommends discussing the risks and benefits of the medication with the healthcare professional. The choice of medication varies depending on a person's medical history. For example, beta-blockers usually are avoided in someone with breathing problems such as asthma. ACE inhibitors and diuretics are especially useful for people with kidney disease or diabetes.

A person who has high blood pressure may be on multiple medications. In fact, the JNC 7 guidelines recommend 2 drugs be used as initial therapy in patients with stage 2 hypertension. The goal of treatment is to keep the systolic pressure below 130 and the diastolic below 85. In a person with diabetes, the goal is a systolic less than 120 and a diastolic below 80.

For an individual with heart disease or kidney disease, the goal is to get the blood pressure as low as can be tolerated.

What are the side effects of the treatments?

The side effects of treatment of high blood pressure vary according to the medications used. Beta-blockers can worsen asthma and may cause dizziness and fatigue. Diuretics can cause dehydration as well as salt and potassium imbalance. Calcium channel blockers can cause swelling of the legs. ACE inhibitors may lead to chronic dry cough. Vasodilators can cause headache and fluid retention. Clonidine, if stopped abruptly, can cause significantly worsened hypertension.

What happens after treatment for the condition?

A person who has high blood pressure needs to continue to take the prescribed medications daily. Blood pressure may return to normal as a result of lifestyle changes. These changes include weight loss, increased physical activity, reduction of alcohol intake, and a diet low in sodium. In most cases, a person will need to continue to take blood pressure medications for life.

How is the condition monitored?

High blood pressure is monitored through frequent visits to a healthcare professional. A person who has high blood pressure should also record blood pressure readings between office visits. Any new or worsening symptoms should be reported to the healthcare professional.