Updated: 05 Jan 2009

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Introduction

High blood pressure is often called "the silent killer". Our guide explains the basics.

We explain what high blood pressure is, look at ways to lower your blood pressure, and provide tips for buying and using a home monitor.

About high blood pressure

One in five adults know they have high blood pressure, but there are many more who don't recognise the problem.

If your blood pressure stays high for a long time, it can greatly increase your risk of heart disease, strokes and kidney failure.

Blood pressure is created by the force of the heart pumping blood around your body. It's measured as two numbers. The higher number (known as "systolic") is the pressure in your blood vessels when your heart contracts. The lower number ("diastolic") is the pressure when your heart is relaxed between heartbeats.

Normal adult blood pressure is around 120/80 millimeters of mercury (mmHg) or lower, though it'll vary. Your blood pressure will be higher if you're stressed, or if you've been exercising a lot. It'll be higher in the afternoon than in the morning. It also increases as you get older and after consuming certain food and drink, like caffeine and salt.

How high is too high?

There's no magic number that means your blood pressure is dangerously high - only your doctor can tell you. But as your blood pressure rises you increase your risk of heart disease and other health conditions.

In general, a doctor will consider it elevated if it's consistently over 140/90. But elevated blood pressure, also called hypertension, doesn't necessarily mean you're at high risk of heart disease. And, conversely, your doctor might think you're at risk even if only one of the two blood pressure measurements is elevated.

In weighing up your risk, your doctor will consider other factors such as your age, gender, family history, weight and whether you are a smoker.

High blood pressure may be inherited. It can also be brought on by illness, pregnancy or certain medicines.

Blood pressure monitors

Some people like to monitor their own blood pressure because it gives them a sense of control over their treatment for high blood pressure. It can also be a good motivator if you're trying to lower your blood pressure by changing your lifestyle.

Your doctor may recommend home monitoring to assess changes in your medication. It's important you take a range of readings over several months and interpret the results with your doctor.

Some people become so anxious when they visit the doctor, their blood pressure shoots up. This is called "white coat hypertension" and it affects about one in five people. Home monitoring can help identify these people and eliminate unnecessary treatment.

Others, however, become anxious when using a home blood pressure monitor. If that's the case for you, don't buy one.

Buying tips

• Get the shop to demonstrate the monitor before you buy.
• If you're buying an arm monitor, make sure the cuff is the correct size for your arm. A cuff that's too narrow may overestimate your blood pressure and a cuff that's too wide may underestimate blood pressure.
• Make sure the buttons and displays are easy to see and read.
• When you first get your monitor take it to your doctor to have its accuracy checked and your technique. Repeat this every six months or so.
• Before using your monitor, read the instruction manual to familiarise yourself with the monitor and recalibrate according to the manufacturer's instructions. If you drop it or readings change abruptly, get it checked.

Using your monitor

• Don't test your blood pressure within 30 minutes of eating, drinking caffeinated drinks, or exercising.
• Relax for a few minutes before testing.
• Remove any jewellery or clothing that interferes with the cuff.
• For arm monitors, rest your arm on a waist-high table. For wrist monitors, keep your wrist level with your heart. It's important to use the same arm position each time you check your blood pressure. If you are seated keep both feet on the floor.
• Take two readings, about one to two minutes apart. If results differ by more than five points take a third reading and record an average of the results.
• Keep a record of all results and discuss these with your doctor.

Home monitors are not a substitute for the regular measurement of blood pressure by your doctor. Don't change your medication based on home readings - check with your doctor first. And talk to your doctor about the most appropriate monitoring regime.

Lowering your blood pressure

Some people can lower or control their blood pressure with a combination of diet, exercise and other lifestyle changes.

• Eat a diet high in fruit, vegetables and wholegrains, and low in fat, especially saturated fat. Reduce the amount of sodium in your diet.
• Be active. On most days, try to spend at least 30 minutes being active. But check with your doctor before you start any vigorous exercise.
• Try to lose excess weight and maintain a healthy weight.
• Limit the amount of alcohol you drink.
• Don't smoke.
• Consider stress-reducing techniques such as yoga, pilates, and meditation or prayer.

If lifestyle changes aren't enough to lower your blood pressure, your doctor may prescribe medication. Medication falls into four main groups - you may be prescribed one or a combination.

Diuretics reduce the amount of salt and water in your blood. This reduces the strain on your heart because there is a smaller volume of fluid to pump around.

Beta-blockers stop the action of the hormone adrenalin. This reduces the workload of the heart by reducing your pulse rate and blood pressure. It also limits the amount your heart rate increases when you exercise.

Calcium channel blockers prevent the movement of calcium through the muscle cells of the blood vessel walls. This causes the arteries to relax, widening the blood vessels, and reducing the pressure inside them.

ACE inhibitors block the production of angiotensin, an enzyme that narrows blood vessels. This allows the artery walls to relax and dilate, which helps reduce the pressure in your blood vessels.

All drugs can have side effects and some should not be used if you have certain conditions. Tell your doctor if you think yours have side effects. Always check with your doctor or pharmacist before you take any new medication, including herbal remedies.

Low blood pressure

If you have low blood pressure, you probably won't need to do anything about it. Though some people faint or feel tired, most people with low blood pressure don't have any associated health problems.

More help

• The National Heart Foundation: ph (09) 571-9191