High blood pressure, also called hypertension, is elevated pressure of the blood in the arteries. Hypertension results from two major factors, which can be present independently or together:
- The heart pumps blood with excessive force.
- The body's smaller blood vessels (known as the arterioles) narrow, so that blood flow exerts more pressure against the vessels' walls.
Blood pressure is the force applied against the walls of the arteries as the heart pumps blood through the body. The pressure is determined by the force and amount of blood pumped and the size and flexibility of the arteries.
Although the body can tolerate increased blood pressure for months and even years, eventually the heart may enlarge (a condition called hypertrophy), which is a major factor in heart failure.Click the icon to see an image of hypertrophic cardiomyopathy.
Such pressure can also injure blood vessels in the heart, kidneys, the brain, and the eyes.
Two numbers are used to describe blood pressure: the systolic pressure (the higher and first number) and the diastolic pressure (the lower and second number). Health dangers from blood pressure may vary among different age groups and depending on whether systolic or diastolic pressure (or both) is elevated. A third measurement, pulse pressure, may also be important as an indicator of severity.
Systolic Blood Pressure. The systolic pressure (the first and higher number) is the force that blood exerts on the artery walls as the heart contracts to pump out the blood. High systolic pressure is a greater risk factor than diastolic pressure for brain, heart, kidney, and circulatory complications and for death, particularly in middle-aged and elderly adults.
Diastolic Blood Pressure. The diastolic pressure (the second and lower number) is the measurement of force as the heart relaxes to allow the blood to flow into the heart. High diastolic pressure is a strong predictor of heart attack and stroke in young adults.
Pulse Pressure. Pulse pressure is the difference between the systolic and the diastolic readings. It indicates stiffness and inflammation in the blood-vessel walls. The greater the difference between systolic and diastolic numbers, the greater the risk to health.Click the icon to see an animation about blood pressure.
There are a number of ways to categorize or describe hypertension.
- Essential Hypertension. Essential hypertension is also known as primary or idiopathic hypertension. About 90% of all high blood pressure cases are this type. The causes of essential hypertension are unknown but are based on complex processes in all major organs and systems, including the heart, blood vessels, nerves, hormones, and the kidneys.
- Secondary Hypertension. Secondary hypertension comprises about 5% of high blood pressure cases. In this condition, the cause has been identified.
Other doctors categorize hypertension based on what portion of the blood pressure reading is abnormal:
Click the icon to see an image of atherosclerosis.
- Isolated Systolic Hypertension. Elevated systolic pressure may pose a significant danger for heart problems and stroke even when diastolic is normal -- a condition called isolated systolic hypertension. This occurs when systolic hypertension is over 140 mm Hg but diastolic pressure is normal. It is related to arteriosclerosis (hardening of the arteries). Isolated systolic hypertension is the most common form of hypertension in people older than age 50.
- Diastolic Hypertension. Diastolic hypertension refers to an elevated diastolic blood pressure reading. This subtype is most common in middle-aged adults age 30 - 50.
Blood Pressure Guidelines
Blood pressure is measured in millimeters of mercury (mm Hg). According to current adult guidelines, blood pressure is categorized as normal, prehypertensive, and hypertensive (which is further divided into Stage 1 and 2, according to severity).
- Normal blood pressure is below 120/80 mm Hg.
- Prehypertension blood pressure readings (120 -139 systolic or 80 - 89 diastolic) indicate an increased risk for developing high blood pressure.
- High blood pressure is greater than or equal to 140 mm Hg (systolic) or greater than or equal to 90 mm Hg (diastolic).
Current guidelines for children are based on percentile ranges for a child’s body size. Hypertension in children is defined as average systolic and diastolic readings that are greater than the 95th percentile for gender, age, and height on at least three occasions.
Prehypertension in children is diagnosed when average systolic or diastolic blood pressure levels are at least in the 90th percentile but less than the 95th percentile. For adolescents, as with adults, blood pressure readings greater than 120/80 are considered prehypertensive. Increasing rates of childhood obesity have led to higher rates of hypertension and prehypertension among children and adolescents.
Blood Pressure Ranges
Blood Pressure Category
Ranges for Most Adults (systolic/diastolic)
Normal Blood Pressure (systolic/diastolic)
Systolic below 120 mm Hg
Diastolic below 80 mm Hg
Systolic 120 - 139 mm Hg
Diastolic 80 - 89 mm Hg
(NOTE: 139/89 or below should be the minimum goal for everyone. People with heart disease, peripheral artery disease, diabetes or chronic kidney disease should strive for 130/80 or less.)
Mild Hypertension (Stage 1)
Systolic 140 - 159 mm Hg
Diastolic 90 - 99 mm Hg
Moderate-to-Severe Hypertension (Stage 2)
Systolic over 160 mm Hg or
Diastolic over 100 mm Hg
Note: If one of the measurements is in a higher category than the other, the higher measurement is usually used to determine the stage. For example, if systolic pressure is 165 (Stage 2) and diastolic is 92 (Stage 1), the patient would still be diagnosed with Stage 2 hypertension. A high systolic pressure compared to a normal or low diastolic pressure should be a major focus of concern in most adults.