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.
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. 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.