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Diastolic and systolic blood pressure: Know your numbers

Have you ever wondered what the top and the bottom blood pressure numbers mean? Doctors call them systolic (the top number) and diastolic (the bottom number) blood pressure.

Knowing them both is important and could save your life.

What does the systolic blood pressure number mean?

When your heart beats, it contracts and pushes blood through the arteries to the rest of your body. This force creates pressure on the arteries. This is called systolic blood pressure.

A normal systolic blood pressure is 120 or below. A systolic blood pressure of 120-139 means you have normal blood pressure that is higher than ideal, or borderline high blood pressure. Even people with this level are at a greater risk of developing heart disease.

A systolic blood pressure number of 140 or higher, on repeated measurements, is considered to be hypertension, or high blood pressure.

What does the diastolic blood pressure number mean?

The diastolic blood pressure number or the bottom number indicates the pressure in the arteries when the heart rests between beats.

A normal diastolic blood pressure number is 80 or less. A diastolic blood pressure between 80 and 89 is normal but higher than ideal.

A diastolic blood pressure number of 90 or higher, on repeated measurements, is considered to be hypertension or high blood pressure.

How is blood pressure measured?

Blood pressure is measured with a simple painless test usually using an electronic blood pressure monitor. This consists of an inflatable cuff that is wrapped around the upper arm and is attached to an electronic monitor that gives a digital readout of the blood pressure and pulse. Some blood pressure cuffs wrap around the forearm or wrist.

The systolic blood pressure number is always said first, and then the diastolic blood pressure number is given. For example, your blood pressure may be read as “120 over 80” or written 120/80.

Blood pressure is measured in millimetres of mercury (mmHg). However, usually the “mmHg” is not used when reporting the blood pressure.

How often should I get my blood pressure checked?

  • If your blood pressure is normal (less than 120/80), get it checked at least once every five years – unless advised to have it measured more frequently. However, as you get older your blood pressure is likely to increase and you should be checked more often, as frequently as your doctor suggests.
  • If your blood pressure is borderline high - systolic blood pressure between 120 and 139 or diastolic blood pressure between 80 and 89 - get it checked at least once a year, or more often as your doctor suggests.
  • If your blood pressure is 140/90 or higher, talk to your doctor as this is high blood pressure and requires a doctor’s attention.
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