Blood pressure is a measurement of the pressure within the arteries when your heart beats. As your heart beats the pressure in your arteries rises and falls. A rise corresponds with the heart contracting forcing blood through and the falls are when the heart is relaxed, waiting for the next heartbeat. When your blood pressure is taken, the measurement is expressed as two numbers e.g. 120/80 mmHg. The first number related to the pressure at the peak of the rise (systolic), and the second as the base of the fall (diastolic). All blood pressures are measured in millimetres of mercury.
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