Hypertension, or high blood pressure, affects approximately 20% of the human population at sometime in their lives. Generally a person is considered hypertensive if his systolic blood pressure is greater than 140 mm Hg and his diastolic blood pressure is greater than 90 mm Hg. However, current methods of evaluation take into consideration combinations of diastolic and systolic blood pressure in determining if a person is suffering from hypertension. In addition, normal blood pressure is age dependent, and classification of an individual as hypertensive depends on the person' age.

Chronic hypertension has an adverse effect on the function of both the heart and the blood vessels. Hypertension requires the heart to perform a greater-than-normal amount of work. This extra work leads to hypertrophy of the cardiac muscle, especially in the left ventricle, and can lead to heart failure. Hypertension also increases the rate at which arteriosclerosis develops. Arteriosclerosis, in turn, increases the probability that blood clots or thromboemboli may form and that blood vessels will rupture. Common conditions associated with hypertension are cerebral hemorrhage, coronary infarction, hemorrhage, coronary infarction, hemorrhage of renal blood vessels, and poor vision caused by burst blood vessels in the retina.

Some conditions leading to hypertension include a decrease in functional kidney mass, excess aldosterone or angiotensin production, and increased resistance to blood flow in the renal arteries. All of these conditions cause an increase in the total blood volume, which causes the cardiac output to increase. The increased cardiac output forces blood to flow through tissue capillaries, causing the precapillary sphincters to constrict. Thus increased blood volume increases the cardiac output and the peripheral resistance, both of which result in a greater blood pressure.

Although these conditions result in hypertension, roughly 90% of the diagnosed cases of hypertension are called either idiopathic or essential, hypertension, which means the cause of the condition is not know. Drugs that dilate blood vessels called vasodilators, drugs that increase the rate of urine production called diuretics, or drugs that decrease cardiac output normally are used to treat essential hypertension. The vasodilator drugs increase the rate of blood flow through the kidneys and thus increase urine production, and the diuretics also increase urine production. Increased urine production reduces the blood volume, which reduces the blood pressure. Substances that decrease cardiac output, such as beta-blocking agents, decrease the heart rate and the force of contraction. In addition to these treatments, low-salt diets normally are recommended to reduce the amount of sodium chloride and water absorbed from the intestine into the bloodstream.