Blood is carried from the heart to all the body's tissues and organs in pipes, called arteries and veins. Blood pressure is the force of the blood pushing against the walls of those pipes. The unit for measuring blood pressure is millimeters of mercury (mmHg).
In most people, hypertension, or high blood pressure, is defined as either:
- a systolic pressure consistently at 140 or higher or
- a diastolic pressure consistently at 90 or higher.
In some groups, such as those with diabetes or kidney disease, a high blood pressure is
- a systolic blood pressure (top number) of 130 or higher or
- a diastolic blood pressure (bottom number) of 80 or higher.
Each time the heart beats (about 60 to 70 times a minute at rest) it pumps blood out into the blood vessels.
When the heart is pumping the blood, it is called systolic pressure.
When the heart is relaxing in between beats, your blood pressure falls; this is the diastolic pressure.
A normal blood pressure is less than 120 (systolic)/80 (diastolic). If the blood pressure is slightly above this, but not yet high enough to be called true hypertension, it is currently called “pre-hypertension.” This term implies that there is a risk of such mild elevation of blood pressure. Although this risk is not as great as with higher blood pressure, the lowering of the pressure is still important.
The higher the pressure over 120/80, the higher the risk of developing cardiovascular complications. Studies show that the association of risk of dying of a heart attack with different levels of blood pressure rises as blood pressure rises. The higher your blood pressure, the higher your risk.
Many people develop high blood pressure during their lifetime. Left untreated, high blood pressure can damage the eyes, kidneys, heart and brain. High blood pressure is a factor in 68 percent of all first heart attacks and 75 percent of all first strokes.
If high blood pressure is left untreated, it can cause:
Enlarged and thickened heart - If the heart has to work harder and longer, it tends to become larger and thicker. Eventually, the heart muscles stretch too much or get too thick. The blood supply to the heart itself, which travels through tiny pipes, called coronary arteries, has difficulty reaching the enlarged and thickened heart. As the heart’s own blood supply falls, the heart begins to suffer and fail.
Much like a body builder who has thick muscles and looks very “stiff” after exercising, the heart also becomes stiff as it thickens. Unfortunately for the heart, this thickening prevents it from relaxing, dilating, and filling with blood. This eventually can also lead to heart failure.
Stroke - As the blood pressure in the brain increases, damage can occur in the lining of blood vessels, forming aneurysms (weakened areas in the blood vessel that may balloon or rupture). When an aneurysm ruptures, this causes a stroke. Possible paralysis, loss of bodily function and motor skills often result.
Uremia(failure of the kidneys to function properly) - Continued high blood pressure causes damage to blood vessels in the kidneys. This reduces the amount of fluid that the kidney can filter out and thus, a build up of waste products occurs.
Atherosclerosis (hardening of the arteries) - The higher the blood pressure, the faster the plaque (collections of fatty material) accumulates in the artery walls.
Heart attack - If one of the coronary arteries that supplies blood to the heart is closed off due to atherosclerosis, portions of the heart muscles are damaged and a heart attack can occur.
Vision loss - High blood pressure can cause blood clots or ruptures in the arterioles in the retina, leading to reduced vision or blindness.
In more than 90 percent of all high blood pressure cases, the exact cause is unknown. This is called primary or "essential" hypertension, and it can be associated with the following factors:
- Race - African-Americans develop high blood pressure more often than Anglo-Americans, and it tends to occur earlier and be more severe.
- Sex - men are more likely to develop high blood pressure than women.
- Age - high blood pressure occurs most often in people over the age of 35.
- Obesity - people who weigh 30 percent or more above their ideal body weight are more likely to develop high blood pressure.
- Sodium sensitivity
- Alcohol consumption
- Oral contraceptives
- Physical inactivity
- Certain drugs such as diet pills or amphetamines
In the remaining 10 percent of all cases, high blood pressure is attributed to kidney disease, a hormonal imbalance, a narrowing of the artery to a kidney, a tumor of one of the adrenal glands, severe snoring while sleeping (called obstructive sleep apnea) or some other anatomic or physiologic abnormality. These cases are called "secondary hypertension," and the blood pressure usually normalizes when the primary problem is treated.
Since there are usually no symptoms, the diagnosis of high blood pressure is made when doing a physical examination for a routine physical or other medical reasons. The medical staff will use an instrument called a sphygmomanometer or “blood pressure cuff”. It consists of a cuff that is wrapped around the upper arm and inflated with air to stop the blood flow in the artery for a few seconds. A valve is opened and air is then released from the cuff. The sounds of the blood rushing through an artery is heard through a stethoscope or other listening device attached to the cuff. The first sound heard is the systolic pressure and the last sound is the diastolic pressure.
The cut-offs from normal levels to high blood pressure, with varying degrees of severity, are as follows:
- Normal: systolic less than 120; diastolic less than 80
- Pre-hypertension: systolic 120-139, diastolic less than 80-90
- High blood pressure
- Stage 1 hypertension: systolic 140-159, diastolic 90-99
- Stage 2 hypertension: systolic above 160, diastolic above 99
Source: Source: The Seventh Report of the Joint National Committee on the Prevention, Detection, Evaluation and Treatment of Hypertension, 2004.
Most clinicians would consider some type of treatment for patients whose systolic pressure (the top number) is above 140 and/or whose diastolic pressure (the bottom number) is above 90. For patients with pressures immediately below these figures (120-139/80-90), the doctor will take into account age and other individual factors before recommending treatment.
A variety of non-pharmacologic approaches to managing hypertension are useful. In some cases of mild hypertension, these approaches are enough to reach satisfactory levels of blood pressure:
- Quit smoking.
- Trim down if you are overweight. Obese people are 2-6 times more likely to develop high blood pressure (and even a small weight loss can improve blood pressure).
- Eat a healthy diet and avoid salty foods.
- Reduce alcohol consumption.
- Begin a program of regular physical activity.
- Get adequate dietary calcium.
- Control your stress.
Acupuncture and biofeedback have been found to be helpful in lowering blood pressure for some people.
If lifestyle changes do not lower your blood pressure enough, the doctor will begin drug therapy. Prescribing diuretics, or water pills, is the first line of treatment for hypertension without any complicating problems, such as heart disease.
Diuretics or "water pills" (thiazide, hydrochlorothiazide, chlorathalidone and indapamide) increase the elimination of salt and water through urination, thereby lessening blood volume and pressure.
Beta-blockers (such as propranolol, atenolol, nadolol, pindolol and labetolol) lower blood pressure by reducing the amount of blood pumped by the heart.
Angiotensin converting enzyme (ACE) inhibitors (captopril, enalapril and lisinopril) lower blood pressure by blocking the production of a hormone known as angiotensin, which increases blood pressure.
Angiotensin receptor blockers (ARB) (candesartan, irebesartan, losartan, olmesartan, telmisartan, vlsartan) lower blood pressure by blocking the effect of angiotensin.
Calcium-channel blockers (nifedipine, nicardipine, verapamil and diltiazem) relax blood-vessel walls, thereby lowering pressure.
Vasodilators (hydralazine and minoxidil) relax the smooth muscle of the peripheral arteries, which causes them to dilate and so reduce the resistance to blood flow.
Centrally acting drugs (clonidine and guanabenz) block the transmission of nerve impulses with the autonomic nervous system, which controls the involuntary action of the heart and blood vessels among other organs.