Blood pressure is measured using an instrument called a sphygmomanometer. It consists of an inflatable cuff, an inflating bulb, and a gauge to show the blood pressure.
The cuff is wrapped around the upper arm, and inflated to a pressure where the pulse in the arm can no longer be heard or felt. The doctor then raises the cuff pressure slightly beyond this point, and then slowly lowers it in order to get a reading of the systolic and diastolic blood pressure.
The systolic reading (the first number of the two) indicates the pressure of blood within your arteries during a contraction of the left ventricle of the heart. The diastolic reading (the second number) indicates the pressure within the arteries when the heart is at rest. Blood pressure is measured in millimetres of mercury (mmHg), for example 120/80 mmHg (known as 120 over 80).
According to the Heart Foundation of Australia, blood pressure just below 120/80 mmHg can be classified as ‘normal’ and blood pressure between 120/80 and 140/90 mmHg is classified as ‘high-normal’.
A person is defined by the Heart Foundation as having high blood pressure (hypertension) if they have a systolic pressure greater than or equal to 140 mmHg and/or a diastolic pressure greater than or equal to 90 mmHg. Hypertension is further classified as mild, moderate or severe as the pressure increases above this level.
Low blood pressure, or hypotension, is not as easy to define as it is usually relative to a person’s normal blood pressure reading, and varies between different people. It generally refers to a blood pressure below an average of about 90/60 mmHg.
It is recommended that you do not smoke or drink caffeine-containing drinks for 2 hours before having your blood pressure monitored, as this can cause an increase in your readings.
It has also been estimated that about 15 per cent of people who have elevated blood pressure readings taken at the doctor’s surgery actually have acceptable levels outside the surgery, when under normal stress levels. This is known as ‘white coat’ hypertension. People with white coat hypertension may benefit from self-monitoring or monitoring of their blood pressure outside the clinic setting. This can be achieved by a person wearing a portable automatic blood pressure machine for 24 hours while they go about their usual daily routine.
Raised blood pressure is a major risk factor for cardiovascular disease, and the higher your blood pressure, the greater your chance of having heart disease or stroke. For this reason it is important that you have your blood pressure monitored regularly, and that you always take any medicine prescribed for hypertension.
Hypertension can also be controlled to a large extent by lifestyle modifications such as reducing excess weight, undertaking regular physical activity, and giving up smoking. Dietary interventions such as reducing your alcohol, salt and fat intake may also help to lower your blood pressure and reduce your absolute risk of cardiovascular disease.
Last Reviewed: 06 November 2009
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