Hypertension.

Hypertension. I INTRODUCTION Hypertension or High Blood Pressure, medical condition in which constricted arterial blood vessels increase the resistance to blood flow, causing an increase in blood pressure against vessel walls. The heart must work harder to pump blood through the narrowed arteries. If the condition persists, damage to the heart and blood vessels is likely, increasing the risk for stroke, heart attack, and kidney or heart failure. Often called the "silent killer," hypertension usually causes no symptoms until it reaches a life-threatening stage. Hypertension affects 20 percent of people living in the United States. Of these, almost a third are unaware of their condition. Until the age of 55, more men than women have hypertension. After that age, the condition becomes more prevalent in women. Hypertension is significantly more common in African Americans of both sexes than in other racial or ethnic groups. Physicians use two measurements to describe blood pressure. Systolic pressure measures blood pressure as the heart contracts to pump out blood. Diastolic pressure measures blood pressure as the heart relaxes to allow blood to flow into the heart. An instrument called a sphygmomanometer measures systolic and diastolic pressure using units of millimeters of mercury (abbreviated mm Hg). Blood pressure is classified in four categories: normal, prehypertension, stage 1 hypertension, and stage 2 hypertension. Normal blood pressure in an adult is less than 120/80 mm Hg, in which 120 describes systolic pressure and 80 describes diastolic pressure. Prehypertension is defined as a systolic pressure of 120 to 139 mm Hg or a diastolic pressure of 80 to 89 mm Hg. People with prehypertension are likely to develop hypertension at some point during their life. Stage 1 hypertension is defined as a systolic pressure of 140 to 159 mm Hg or a diastolic pressure of 90 to 99 mm Hg. Stage 2 hypertension is defined as 160/100 mm Hg or higher. II HOW HYPERTENSION DEVELOPS Two factors determine blood pressure: the amount of blood the heart pumps and the diameter of the arteries receiving blood from the heart. When the arteries narrow, they increase the resistance to blood flow. The heart works harder to pump more blood to make sure the same amount of blood circulates to all the body tissues. The more blood the heart pumps and the smaller the arteries, the higher the blood pressure. The kidneys play a major role in the regulation of blood pressure. Kidneys secrete the hormone renin, which causes arteries to contract, thereby raising blood pressure. The kidneys also control the fluid volume of blood, either by retaining salt or excreting salt into urine. When kidneys retain salt in the bloodstream, the salt attracts water, increasing the fluid volume of blood. As a higher volume of blood passes through arteries, it increases blood pressure. Scientists do not fully understand the causes of hypertension. In up to 95 percent of cases no clear cause can be identified. This type of high blood pressure is known as essential hypertension, and scientists suspect that genetic factors may play a role in its development. In about 5 percent of cases high blood pressure develops as a result of another medical disorder, such as kidney or liver disease, or as a side effect of certain medications. This type of high blood pressure is known as secondary hypertension. Other factors that may contribute to elevated blood pressure in some people include a diet high in salt, physical inactivity, obesity, and heavy alcohol consumption. III COMPLICATIONS If hypertension is not detected and treated, life-threatening complications develop over a course of years. Increased pressure on the inner walls of blood vessels makes the vessels less flexible over time and more vulnerable to the buildup of fatty deposits in a process known as atherosclerosis (see Arteriosclerosis). Weakened portions of the blood vessel wall may balloon, forming an aneurysm. If an aneurysm ruptures, internal hemorrhaging (bleeding) results. Both atherosclerosis and a ruptured aneurysm in the brain can lead to a stroke. Hypertension forces the heart to work harder to pump adequate blood throughout the body. This extra work causes the muscles of the heart to enlarge, and eventually the enlarged heart becomes inefficient in pumping blood. An enlarged heart may lead to heart failure, in which the heart can not pump enough blood to meet the body's needs. Increased blood pressure may damage the small blood vessels within the kidney. The kidney then becomes unable to filter blood efficiently, and waste products may build up in the blood in a condition known as uremia. Without medical treatment, kidney failure will result. IV TREATMENT Physicians recommend that people with prehypertension undergo diet and lifestyle changes, such as losing weight and quitting smoking, in order to prevent a rise in blood pressure. Some patients can lower their blood pressure by limiting salt in their diet. Increasing physical activity and reducing alcohol consumption to less than two drinks per day for men and one drink per day for women may also lower blood pressure. For those with stage 1 and stage 2 hypertension, a physician may prescribe diet and lifestyle changes, as well as one or more drugs known as antihypertensives. Diuretics are antihypertensives that promote excess salt and water excretion, reducing the amount of fluid in the bloodstream and relieving pressure on blood vessel walls. Beta blockers reduce heart rate and the amount of blood the heart pumps. ACE inhibitors prevent the narrowing of blood vessel walls to control blood pressure. Calcium channel blockers slow heart rate and relax blood vessels. Studies show that two drugs are more effective than one drug at lowering blood pressure to less than 140/90 mm Hg. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.