Blood pressure (BP)

Blood pressure (BP) refers to how hard the blood is pushing on the major blood vessels as it is pumped around the body by the heart. It is measured in millimetres (mm) of mercury (a liquid silver metal, which has the chemical symbol Hg), so blood pressure measurements are expressed as a number followed by mmHg. The images below remind you how to measure the blood pressure at two points in time: when the heart contracts and when it relaxes.

A healthworker measuring blood pressure

A healthworker measuring blood pressure. (Photo: Basiro Davey)

Diagram showing blood pressure measurement

The pressure in the cuff is increased until the blood flow stops, and then the flow gradually returns as the cuff is slowly deflated. This enables you to measure the blood pressure when the artery is closed by pressure from the cuff, and when the artery is fully open.

A blood pressure measurement is two numbers written one above the other. The top number tells you the systolic pressure, which is the pressure at the moment the heart beats and pushes blood into the body. The bottom number tells you the diastolic pressure when the heart relaxes between each beat so it can refill with blood. Healthy blood pressure stays at or above 90/60 mmHg, but should not reach as high as 140/90 mmHg.

Last modified: Friday, 4 July 2014, 10:05 AM