High Blood Pressure: Measurements and Medications Blood doesn't flow in a steady stream, but moves through the circulatory system in spurts determined by your heart's beats. With each beat, about two ounces of freshly oxygenated blood is forced out of the left ventricle (the main pumping chamber) into the aorta and into the body's 60,000 miles of blood vessels. The tension or force that is placed on the inside walls of arteries to keep blood flowing is known as "blood pressure." Your blood pressure is constantly changing, depending on how hard the heart is working. During exercise, for instance, the heart can pump up to three times as fast as during periods of rest. Between heartbeats the heart muscle rests momentarily and gets ready for the next beat. Blood pressure is measured by two numbers, such as 110 over 70 or 110/70. The higher number, called the systolic pressure, is the highest pressure in your arteries when your heart contracts to exert maximum force on the walls of blood vessels during a heartbeat. The lower number, called the diastolic pressure, is the lowest pressure in your arteries when your heart relaxes momentarily between beats and fills with blood. How It's Measured Blood pressure is measured in millimeters of mercury (mm Hg). This unit refers to how high the pressure inside your arteries can raise a column of mercury. A typical normal blood pressure is considered to be 120/80 mm Hg, and high blood pressure is generally categorized as consistent readings of 140/90 mm Hg or higher; severe high blood pressure constitutes a reading of 200/115 mm Hg. A doctor shouldn't make a diagnosis of high blood pressure based on a single reading. Normal blood pressure refers to your pressure when you 're resting, but your blood pressure varies with exercise, strong emotion and stress. What's more, blood pressure increases gradually with age as the artery walls become less elastic. Blood pressure is usually measured with a sphygmomanometer, a device that consists of an inflatable rubber cuff, an air pump, and a column of mercury or a dial or digital readout reflecting pressure in the air column. The cuff is wrapped around the upper arm and tightened until blood flow through the large artery in the arm is stopped. As air is pumped into the cuff, it pushes up a column of mercury or air. The doctor or nurse places a stethoscope over the artery and listens first for the cessation of blood flow, then as the cuff is loosened, the first thumping sound of blood flow resuming in the vessels. The height of the mercury or air indicates the systolic pressure. The pressure when the thumping sound stops is the diastolic pressure. While doctors had thought that the presence of hypertension required both an elevated systolic (first number) and diastolic (second number), they now classify you as having high blood pressure if either your systolic pressure exceeds 140 or your diastolic is greater than 90. High blood pressure is not a condition to take lightly, because it can damage components of the circulatory system including the blood vessels of the heart, brain, eyes and kidneys. And the longer it goes undiagnosed and untreated, the worse the outlook, because it forces your heart to work harder than normal. Blood pressure is like a weight or load that the heart muscle must lift, and like any muscle, your heart gets larger with heavy work. Eventually, the muscle can no longer adapt to the excessive work load, and the heart's pumping efficiency decreases. If this occurs, the heart muscle may weaken and heart failure may develop. High blood pressure also accelerates the development of atherosclerosis in your arteries as you age, increasing the chances of a stroke or heart attack. And by putting increased pressure on your artery walls, high blood pressure also can lead to an aneurysm, a bulge in a weakened artery. Because high blood pressure is a risk factor for so many forms of heart disease, it's important to get it under control. Many studies have demonstrated a direct relationship between high blood pressure and stroke, coronary artery disease, heart failure and kidney failure. Compared with people whose high blood pressure is under control, those with uncontrolled high blood pressure are about 3 times more likely to have coronary artery disease, about 6 times more likely to have congestive heart failure, and about 7 times more likely to have a stroke. Know Your Numbers Systolic (first number) Less than 130 mm Hg: normal blood pressure; recheck within two years 130 to 139 mm Hg: High normal; recheck within one year 140 to 150 mm Hg: mild high blood pressure; recheck within two months 160 to 179 mm Hg: moderate high blood pressure; see your doctor within one month 180 to 209 mm Hg: severe high blood pressure; see your doctor within one week 210 mm Hg or higher: very severe high blood pressure; see your doctor immediately Diastolic (second number) Less than 85 mm Hg: normal blood pressure;  recheck within 2 years 85 to 89 mm Hg: high-normal blood pressure; recheck within 1 year 90 to 99 mm Hg: mild high blood pressure; recheck within 2 months 100 to 109 mm Hg: moderate high blood pressure; see your doctor within 1 month 110 to 119 mm Hg: severe high blood pressure; see your doctor within 1 week 120 mm Hg or higher: very severe high blood pressure; see your doctor immediately Treatment A kidney disorder, adrenal gland or pituitary tumor, defects or constriction of the aorta or thyroid disease are sometimes the underlying cause of high blood pressure; but in more than 90 percent of cases, no specific cause can be found. If you have high blood pressure, it's very important to work with your doctor to get your blood pressure down to safe levels. Treatment may include lifestyle changes (losing weight may be all that's necessary), drug therapy or some combination of both. In fact, one recent study called the Dietary Approaches to Stop Hypertension Trial (DASH) found that a diet high in fruits, vegetables and low-fat dairy products may be enough on its own to reduce blood pressure in some people. In the DASH trial, people with high blood pressure, (averaging 160/95) were split into two groups, each following a slightly different diet. One was the typical American diet, consisting of 3.5 pieces of fruit and vegetables a day, one-half serving of low-fat dairy products, and 3.5 servings of fish, poultry or meat. The second diet consisted of nine pieces of fruit or vegetables, 3.5 servings of low-fat dairy products and only about two servings of fish, poultry or meat. The study found that people who followed the second diet lowered their blood pressure to an average of 150/90, while blood pressure did not change in those following the typical American diet. Besides eating right, here's what experts generally recommend for controlling high blood pressure: Don't smoke. Smoking promotes artherosclerosis and contributes to high blood pressure. Lose weight (if necessary). Weight loss lowers blood pressure, eases the burden on your heart and may prevent diabetes and its complications. Reduce salt intake to about 2,500 milligrams a day. Cutting down on salt (actually the sodium it contains) may lower your blood pressure, as about two-thirds of Americans are sensitive to salt. Since it's hard to know whether your blood pressure is affected by salt, it pays to cut back if you have hypertension or are at risk for it. Excess sodium encourages the body to retain fluid. This excess fluid puts undo strain on the heart by increasing the volume of blood, leaving the heart with more to pump. Excess fluid in the body's tissues is a problem for people with congestive heart failure. It may also interfere with certain fluid-reducing medications, such as diuretics. Increase fiber in your diet, especially soluble fiber (found in oat bran, beans, pears and apples, for example). Soluble fiber binds with bile acids in the intestine so that they are excreted instead of being absorbed into the bloodstream. The result, increased formation of bile acids from cholesterol, can lower blood cholesterol levels. Limit alcohol to no more than one ounce a day. That's about the amount of alcohol in one mixed drink, a glass of wine or a bottle of beer. Larger amounts of alcohol can raise blood pressure. Increase physical activity to at least three times per week, for about 30 minutes per session. Exercises best for controlling blood pressure are aerobic activities like walking, running, swimming, bicycling or others that boost your heart rate and keep it high for an extended period of time. Practice a regular form of relaxation therapy, such as meditation, yoga or biofeedback. That's because blood pressure tends to increase during periods of uncontrolled stress. Medications There are many drugs that can control blood pressure effectively with different modes of action and different side effects. These medications are divided into seven categories: diuretics, vasodilators, alpha-blockers, beta-blockers, ACE inhibitors, angiotensin receptor blockers and calcium channel blockers. Within each category are a number of different drugs. Because of their variety, as well as their variable actions (age, race and severity of hypertension make a difference) and side effects, national consensus guidelines have been developed as a standardized approach to treating hypertension. The first step is to try to lower your blood pressure with lifestyle changes. If this effort doesn't reduce pressure sufficiently or if the level of blood pressure is very high, drugs are added. Your doctor may first prescribe a diuretic or beta-blocker. If these drugs aren't effective, your doctor has three treatment options: increase the dose, substitute another drug, or add a second drug from a different class of antihypertensives. If your blood pressure still is not controlled, a third drug may be added. It may take trying a number of different drug combinations before you and your doctor find the drug or drugs that work best for you. Don't get discouraged during this phase. It's important for you to follow your doctor's advice, return as advised to check your blood pressure and tell your doctor how you are adjusting to the medications. Working together, you'll find the best way to reduce your blood pressure and your risk of heart disease or a stroke.  Drug Category : Diuretics How they Work : By helping the kidneys remove sodium and extra water Some Common Agents: Chlorthalidone, chlorthiazide, hydrochlorthiazide  Drug Category : ACE inhibitors How they Work : By dilating arteries and decreasing the resistance of the blood pumped from the heart Some Common Agents: Captopril, Enalapril, Lisinopril  Drug Category : Angiotensin Receptor Blockers  How they Work: Like ACE inhibitors, by dilating arteries and decreasing the resistance to blood flow Some Common Agents: Losartan, Valsartan  Drug Category: Vasodilators How they Work : By relaxing the muscles in the walls of the blood vessels Some Common Agents: Hydralazine, Minoxidil  Drug Category : Calcium Channel Blockers How they Work : By slowing the flow of calcium into blood vessels, which in turn relaxes the vessels Some Common Agents: Diltiazem, Verapamil, Nifedipine  Drug Category : Alpha-blockers How they Work : By relaxing the nerves that are central to regulating blood pressure Some Common Agents: Terazosin, Doxazosin  Drug Category : Beta-blockers How they Work : By blocking receptors in the brain that are increasing blood pressure Some Common Agents: Metoprolol, Propranolol, Atenolol