Understanding Blood Pressure

What the numbers mean, why they matter and how to measure blood pressure accurately

Blood pressure is one of the most useful measurements in preventive healthcare.

It is also one of the easiest to misunderstand.

A single high reading does not necessarily mean you have hypertension. A “normal” result does not guarantee that your cardiovascular risk is low. Blood pressure changes naturally with activity, stress, pain, sleep, medicines and the way it is measured.

The aim is not to chase a perfect number. It is to establish whether your usual blood pressure is healthy for you and, when it is raised, reduce the risk of heart attack, stroke, heart failure and kidney disease.

What is blood pressure?

Blood pressure is the force of blood pushing against the walls of your arteries.

It is written as two numbers, such as 120/80 mmHg.

The first number is the systolic blood pressure. It measures the pressure in your arteries when your heart contracts and pumps blood.

The second number is the diastolic blood pressure. It measures the pressure when your heart relaxes between beats.

The unit mmHg means millimetres of mercury, reflecting the traditional method used to measure pressure.

Your blood pressure rises and falls throughout the day. Exercise, emotion, caffeine, smoking, temperature, pain and even a full bladder can temporarily affect the result.

What do the numbers mean?

For most adults, Australian patient guidance describes blood pressure broadly as:

• Optimal: below 120/80 mmHg
• Normal: systolic 120–129 and/or diastolic 80–84
• High-normal: systolic 130–139 and/or diastolic 85–89
• High blood pressure: persistent readings of 140/90 mmHg or higher

These ranges are useful, but they are not a personalised treatment plan.

Your ideal blood pressure depends on factors such as age, frailty, diabetes, kidney disease, cardiovascular disease, pregnancy, falls risk and how well you tolerate treatment.

Why high blood pressure matters

High blood pressure is also called hypertension.

It often causes no symptoms. Many people feel completely well while raised pressure gradually damages their arteries and organs.

Over time, hypertension can increase the risk of:

• Heart attack
• Stroke
• Heart failure
• Chronic kidney disease
• Peripheral vascular disease
• Some forms of cognitive decline
• Eye damage

Because it is usually silent, regular measurement matters more than waiting for symptoms. Australian adults should generally have their blood pressure checked at least every two years, with more frequent checks when readings are elevated or cardiovascular risk is higher.

One high reading is not always hypertension

Blood pressure varies, and the circumstances of measurement matter.

Some people develop white-coat hypertension, where their readings are raised in a clinic but lower at home. Anxiety, rushing to the appointment, pain or talking during the measurement may contribute.

The opposite can also occur. Masked hypertension means clinic readings appear acceptable while readings at home or during daily life are consistently high.

For this reason, your GP may confirm an elevated result using:

• Repeated clinic measurements
• Home blood-pressure monitoring
• A 24-hour ambulatory blood-pressure monitor

A 24-hour monitor records readings regularly through the day and night and can show how your pressure changes during normal activities and sleep.

How to measure blood pressure properly

Small errors in technique can produce misleading results.

For a reliable home reading:

1. Avoid smoking, vaping, caffeine and strenuous exercise for at least 30 minutes beforehand.
2. Empty your bladder.
3. Sit quietly for five minutes.
4. Sit with your back supported.
5. Keep both feet flat on the floor and your legs uncrossed.
6. Support your bare arm so the cuff is near heart level.
7. Use an automatic, validated upper-arm monitor with the correct cuff size.
8. Remain still and do not talk during the reading.
9. Take two readings about one minute apart.
10. Record both results.

Your GP may ask you to measure your blood pressure morning and evening for seven days, or for at least five days when seven is not practical. Follow the specific instructions provided by your clinician.

The cuff size matters

A cuff that is too small can give a falsely high result. A cuff that is too large may also affect accuracy.

The inflatable part of the cuff should fit your upper arm correctly. People with larger or smaller arms may need a different cuff from the one supplied as standard.

Wrist and finger monitors are generally more sensitive to positioning and are usually not the first choice when an appropriate upper-arm device can be used.

Look for a monitor that has been independently validated for accuracy rather than choosing only by price, brand or online reviews.

What causes high blood pressure?

In most people, there is no single identifiable cause. This is called primary or essential hypertension.

Risk tends to increase with age and may be influenced by:

• Family history
• Excess dietary salt
• Low physical activity
• Excess body weight
• Regular heavy alcohol use
• Smoking
• Poor sleep
• Obstructive sleep apnoea
• Diabetes
• Kidney disease

A smaller proportion of people have secondary hypertension, meaning another condition or substance is contributing.

Possible causes include:

• Kidney disease
• Narrowing of a kidney artery
• Hormonal conditions
• Obstructive sleep apnoea
• Pregnancy-related hypertension
• Certain prescription medicines
• Anti-inflammatory medicines
• Decongestants
• Stimulants or illicit drugs

Your GP may investigate secondary causes when hypertension begins unusually young, becomes suddenly worse, is very difficult to control or is accompanied by other concerning findings.

How can blood pressure be lowered?

The most effective plan depends on your readings and your overall cardiovascular risk.

Reduce excess salt
Much of the salt in an Australian diet comes from packaged, processed and takeaway food rather than salt added at the table.

Checking labels, choosing lower-sodium options and eating more minimally processed food can help.

Be physically active
Regular aerobic activity and strength exercise can reduce blood pressure and improve cardiovascular health.

Build gradually if you have been inactive or have significant health conditions.

Work towards a healthier weight
Where excess weight is contributing, even modest weight loss may improve blood pressure.

Limit alcohol
Alcohol can raise blood pressure, particularly when intake is frequent or heavy. Alcohol-free days and smaller serves can help.

Stop smoking
Smoking may not be the sole cause of persistent hypertension, but it substantially increases the damage associated with cardiovascular risk.

Prioritise sleep and assess sleep apnoea
Loud snoring, witnessed pauses in breathing, morning headaches and excessive daytime sleepiness can suggest obstructive sleep apnoea, which is associated with hypertension.

Several measures together usually have a greater effect than one change alone.

When are medicines needed?

Lifestyle measures remain important, but they are not always enough.

Your GP may recommend blood-pressure medicine when:

• Blood pressure remains persistently high
• Your overall cardiovascular risk is elevated
• You have diabetes, kidney disease or established cardiovascular disease
• Your readings are markedly elevated
• Organ damage related to hypertension is suspected

Australian cardiovascular-risk guidance recommends treatment for very high blood pressure, such as systolic pressure of at least 160 mmHg or diastolic pressure of at least 100 mmHg, even when calculated overall cardiovascular risk is otherwise low.

Common medicine groups include ACE inhibitors, angiotensin receptor blockers, calcium-channel blockers and diuretics. Some people need more than one medicine because different medicines lower blood pressure in complementary ways.

Do not stop treatment simply because your readings have improved. They may be controlled because the medicine is working.

Speak with your GP if you develop dizziness, ankle swelling, cough, fatigue, erectile difficulties or another possible adverse effect. Treatment can often be adjusted.

Can blood pressure be too low?

A relatively low reading can be normal when you feel well.

Low blood pressure becomes more important when it causes:

• Dizziness
• Fainting
• Blurred vision
• Weakness
• Falls
• Confusion

A fall in blood pressure after standing is called orthostatic or postural hypotension. It may be related to dehydration, medicines, illness or problems with the body’s automatic blood-pressure control.

New, worsening or recurrent symptoms deserve assessment, particularly in older adults or people taking several medicines.

When is high blood pressure urgent?

A very high number alone needs prompt medical advice, but the presence of symptoms is especially important.

Call 000 for severe or sudden symptoms such as:

• Chest pain
• Severe shortness of breath
• Collapse
• New weakness or numbness
• Difficulty speaking
• Confusion
• Seizure
• Sudden severe visual disturbance

Do not delay emergency care to repeat the reading multiple times at home.

Start with one change

Choose one useful first step:

• Have your blood pressure checked
• Ask whether you need home monitoring
• Check that your cuff fits correctly
• Reduce one regular high-salt food
• Walk for ten minutes most days
• Arrange help to stop smoking
• Take your prescribed medicine consistently

A reliable series of readings is more useful than becoming anxious about one isolated number.

The bottom line

Blood pressure is not a fixed number and should not be judged from one rushed measurement.

Persistent readings of 140/90 mmHg or higher generally require assessment, but your GP will interpret them alongside home readings, medical history and overall cardiovascular risk.

Measure carefully, look for the pattern and act early when blood pressure remains elevated. Good control can substantially reduce the risk of heart attack, stroke, kidney disease and heart failure.