Blood Pressure Overview
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels. During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure. The blood pressure in the circulation is principally due to the pumping action of the heart. Differences in mean blood pressure are responsible for blood flow from one location to another in the circulation. The rate of mean blood flow depends on the resistance to flow presented by the blood vessels. Mean blood pressure decreases as the circulating blood moves away from the heart through arteries and capillaries due to viscous losses of energy.
| Category |
Systolic (Top number) |
|
Diastolic (Bottom number) |
| Normal |
Less than 120 |
and |
Less than 80 |
| Pre-hypertension |
120–139 |
or |
|
| High blood pressure |
|
|
|
| Stage 1 |
140–159 |
or |
90–99 |
| Stage 2 |
160 or higher |
or |
100 or higher |
The ranges in the table apply to most adults (aged 18 and older) who don't have any serious history of illnesses.
Blood pressure rises with each heartbeat and falls when heart relaxes between beats. While BP can change from minute to minute with changes in posture, exercise, stress or sleep, it should normally be less than 120/80 mm Hg (less than 120 systolic AND less than 80 diastolic) for an adult age 20 or over.
Typically more attention is given to the top number (the systolic blood pressure) as a major risk factor for cardiovascular disease for people over 50 years old. In most people, systolic blood pressure rises steadily with age due to increasing stiffness of large arteries, long-term build-up of plaque, and increased incidence of cardiac and vascular disease.
