What is Blood Pressure

Blood pressure is the amount of force your blood exerts against the walls of your arteries. Normal blood pressure effectively and harmlessly pushes the blood from your heart to your body's organs and muscles so they can receive the oxygen and nutrients they need. Blood pressure is variable—it rises and falls during the day. When blood pressure stays elevated over time, however, it is called high blood pressure or hypertension.
According to the most recent estimates, about 73 million Americans age 20 and older have hypertension and nearly half are women, according to the American Heart Association. High blood pressure killed nearly 54,707 Americans in 2004 and was listed as a primary or contributing factor in 300,000 deaths. Hypertension can occur in both children and adults, but it is more common in adults, particularly African Americans and the elderly.
People with other conditions such as diabetes and kidney disease are likely to become hypertensive. In addition, being overweight, drinking alcohol excessively (defined as more than two drinks a day for men and one drink a day for women), and taking oral contraceptives may increase blood pressure. Overall, nearly one in three American adults has hypertension. About half of the 73 million Americans with high blood pressure are women. More men than women have hypertension, until women reach menopause, when their risk becomes greater than men's. An estimated 27 percent of women have high blood pressure.
Blood pressure is typically expressed as two numbers, one over the other, and is measured in millimeters of mercury (noted as mm Hg). The first number is the systolic blood pressure, the pressure used when the heart beats. The second number, diastolic blood pressure, is the pressure that exists in the arteries between heartbeats.Depending on your activities, your blood pressure may increase or decrease throughout the day. If you are not acutely ill, are over 18 years of age and are not taking antihypertensive drugs, a blood pressure reading of 119 mm Hg or below systolic and/or 79 mm Hg or below diastolic (119/79) is considered normal. If your systolic blood pressure is 120 to 139 mm Hg systolic and/or your diastolic pressure is 80 to 89 mm Hg, you have prehypertension. This means that you don't have high blood pressure now but are more likely to develop it in the future, and you have increased risk factors for cardiovascular disease and other conditions related to hypertension.
A blood pressure level of 140/90 mm Hg or higher is considered high. You have stage 1 hypertension if your systolic pressure is 140 to 159 and/or diastolic is between 90 and 99. If your systolic pressure is 160 or above and/or your diastolic is100 or more, you have stage 2 hypertension. Only one of the numbers needs to be above normal for a diagnosis of high blood pressure; that is, you can have isolated systolic or diastolic hypertension. Isolated systolic hypertension (ISH) is the most common form of high blood pressure in older Americans. The National Heart, Lung, and Blood Institute (NHLBI) estimates that 65 percent of people with hypertension over age 60 have ISH. The cause of approximately 90 to 95 percent of all hypertension isn't known. This type of hypertension is called primary or essential high blood pressure. Secondary hypertension is somewhat different because it represents all of the specific diseases that cause elevated blood pressure.