Blood pressure is the pressure exerted by the blood against the inner walls of the blood vessels, especially the arteries (see the chapter on Blood Pressure). The blood pressure changes from minute to minute and is influenced by many factors such as activity, age, health, emotional tension, and so on. With each heartbeat, about 70 ml of blood is ejected from the heart and propelled through approximately 100,000 km of blood vessels. Constriction of the blood vessels (arteries) causes high blood pressure and greatly increases the work of the heart. Arteries are traumatized by high blood pressure and this increases the development of hardening of the arteries owing to plaques of atheroma (atherosclerosis). The heart may enlarge, arteries may become gradually blocked, and circulation to the heart muscle, the brain, and other organs may slowly become impaired until one day there will be an emergency situation such as a sudden heart attack or stroke. It is true that hypertension maims and kills millions through preventable complications.
Clinical trials during the past 20 years have revolu¬tionized the treatment of hypertension with and without drugs. Many familiar (old) drugs have been rendered obsolete because of newer, safer, and more effective alternatives.

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• I. MEASUREMENT OF BLOOD PRESSURE
  The instrument used to measure blood pressure is called a sphygmomanometer. It measures the air pressure needed to raise a column of mercury (Hg). The instrument consists of an inflatable cuff connected to a small bulb pump and a pressure gauge. By means of the inflatable cuff, which encircles the limb (usually the upper arm), air pressure within the cuff is balanced against the pressure in the artery (usually the brachial artery at the elbow). The pressure is estimated by means of a mercury or aneroid manometer. The mercury manometer is the most accurate pressure gauge. The aneroid gauge is frequently used instead of the mercury manometer because it is more compact and is convenient as a portable instrument. Some electronic instruments may give falsely high diastolic readings, but manufacturers will improve these to meet market demands.
• II. HOW HIGH IS HIGH?
  The World Health Organization (WHO) and many experts agree that in individuals under age 65, a systolic blood pressure equal to or greater than 140 mmHg and a diastolic blood pressure of 90 mmHg or above is ab¬normal. Optimal systolic blood pressure is less than 120 mmHg and optimal diastolic blood pressures are less than 80 mmHg. In patients age 65–80 a systolic pressure greater than 165 on three or more readings weeks or months apart is considered hypertension. The Framingham Study and other studies indicate a significant increase in car¬diovascular risk in individuals with a blood pressure in the borderline range. An individual is considered to have high blood pressure if several readings exceed 140/90, especially if three consecutive readings are elevated. The risk at any level of hypertension, including borderline hypertension, is greatly increased by smoking or a high blood cholesterol. Mild hypertension is extremely common, and over a 10- to 15-year period increases the risk of stroke, heart attack, and heart failure. Clinical studies have documented that blacks develop organ damage (stroke, heart failure, and damage to the kidneys) much quicker than whites at the same level of hypertension.
• III. CAUSES OF HYPERTENSION A. Primary (Essential) Hypertension
  In the majority of cases of hypertension, no detectable underlying disease is present. There are several theories as to why the blood pressure may be increased. This type
• IV. PATHOGENESIS OF PRIMARY ESSENTIAL HYPERTENSION
  A. Salt Hypothesis
• V. COMPLICATIONS
  A. Effects on Arteries and Heart
• VI. SYMPTOMS
  There is little doubt that hypertension either leads to early death or inflicts serious physical handicaps to millions. Blood pressure may be mildly or moderately elevated for several years without symptoms until the occurrence of stroke, heart attack, or heart failure.
• VII. INVESTIGATIONS
  Blood, urine, and other tests are performed to determine if hypertension is primary, that is, without a cause, or secondary to diseases of organs, especially the kidney. These tests will also serve as a baseline for future com¬parison and as a means for detecting side effects of some antihypertensive drugs. The tests and the reasons for their use are listed below.
• VIII. NONDRUG TREATMENT
  The majority of patients with mild primary hypertension are advised to persist with a one-year trial of nondrug treatment. It is important to understand the essential requirements of the program. The hypertensive must be aware of the dangers of the so-called silent killer to become sufficiently motivated to comply with self-imposed treatment. Individuals who persist with nondrug treatment
• IX. DRUG TREATMENT
  A. Number of Drugs Available
• BIBLIOGRAPHY
  ALLHAT: Officers and Coordinators for the ALLHAT Collabo¬rative Research Group. JAMA, 288:2981–2997, 2002. ALLHAT: The Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial. Major cardiovascular events in hypertensive patients randomized to doxazosin vs. chlorthalidone. The ALLHAT