Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels and is one of the principal vital signs. During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure. The mean blood pressure, due to pumping by the heart and resistance to flow in blood vessels, decreases as the circulating blood moves away from the heart through arteries. Blood pressure drops most rapidly along the small arteries and arterioles, and continues to decrease as the blood moves through the capillaries and back to the heart through veins. Gravity, valves in veins, and pumping from contraction of skeletal muscles, are some other influences on blood pressure at various places in the body. Hypertension (high blood pressure) may be divided into three types:
- Mild Hypertension: The systolic blood pressure ranges between 140 and 160 and the diastolic blood pressure ranges between 90 and 100.
- Moderate Hypertension: The systolic blood pressure ranges between 160 and 200 and the diastolic blood pressure ranges between 100 and 120.
- Severe Hypertension: The systolic blood pressure is above 200 and the diastolic blood pressure is above 120.