Blood pressure basics

What is blood pressure?

Blood pressure is simply the pressure inside blood vessels (arteries). It is created by the pumping action of the heart and the ease with which the blood flows through the blood vessels.

Why is it important?

High blood pressure is not a disease, but it is a risk factor for heart disease and strokes.

High blood pressure is also usually silent meaning that people cannot normally feel it. This means that it is important to have it checked on a regular basis especially as you get over age 40.

How is it measured?

Blood pressure is measured by using a machine called a sphygmomanometer.

Previously, blood pressure machines used columns of mercury. The blood pressure reading was given by the height of the column of mercury in millimetres. Since Hg is the symbol for mercury, the units of blood pressure even now are mmHg.

Mercury is a poisonous substance so it was banned for medical use in blood pressure machines and thermometers. The new digital automatic blood pressure machines work by sensing the vibrations in the blood vessel walls. They are very accurate and are often used in clinics and hospitals.

What do the blood pressure readings mean?

Blood pressure machines will give you 2 numbers. For example 120/80. Some also give a third number which is the pulse or your heart rate per minute.

The first or top number is always the higher one of the 2 numbers. It is called the systolic pressure and is caused by the actual pumping action of the heart. In the example above the systolic pressure is 120 mmHg.

The second or bottom number is always lower than the first one. It is called the diastolic pressure and is the pressure in the blood vessels when the heart muscle is relaxing between pumping actions. In the example above the diastolic pressure is 80 mmHg.

Some blood pressure machines also give a third number which is the pulse or your heart rate per minute.

You can see these 3 numbers: systolic pressure, diastolic pressure and pulse from top to bottom in the image below.

What is a normal blood pressure reading?

Blood pressure varies with age, gender and weight to name a few things. Many people quote 120/80 as a normal blood pressure but that is the average for a 21 year old, 70 kg man. Currently, guidelines say that anyone with a blood pressure regularly over 140/90 needs to adjust their lifestyle and may need medicine.

Blood pressure also changes with the time of day. It is usually lowest at night when we are sleeping and then rises sharply in the morning and gets steadily higher during the course of the day. It then starts getting less in the evening. Take a look at the graph below which gives you a good idea of what you can expect.

Monitor your own blood pressure

You can check your own blood pressure using machines at your local clinic in the waiting room and at many pharmacies. People who suffer from high blood pressure often buy their own machines so that they can keep an eye on it.

If you are considering buying your own blood pressure machine, then make sure to get the ones where the cuff goes around the upper arm rather than the wrist. You do not usually need to spend a lot of money on them because they are all pretty accurate. The more expensive ones have various bells and whistles but do not measure the blood pressure with any greater accuracy.

I have selected a couple below from the Omron range that we use in UK general practice. However, feel free to choose any other brand as they have all passed tests for accuracy to enable them to be sold in the UK market.

Get the right size cuff for your arm

You just need to make sure that the machine comes with a cuff which is the right size for your upper arm. The first machine below (M2) has a standard size cuff up to 32 cm diameter. The second machine in this list (M6) has a cuff big enough for people with large arms up to 42cm diameter.

Read next:

How to manage your blood pressure