Everything you need to know about your blood pressure

04 February 2019

''In order for blood to go round the body and supply your vital organs with oxygen and nutrients it must be kept under pressure – much like the water in your central heating system at home. Blood moves from higher pressures in the arteries – the vessels which take the blood away from the heart – to low pressure in the veins. Your heart acts as a pump to keep the blood moving round but it can’t work without pressure in the system – just like your boiler stops working if a pipe bursts at home.

When we talk about your blood pressure, we mean the pressure in the arteries and we can measure this easily with a blood pressure cuff – you can even do this at home yourself with a relatively cheap machine. Generally we talk about two figures – the systolic value, which is the higher number, and the diastolic value, which is the lower number. So you will be given a value for your blood pressure of one number over another number e.g. 130/80. The units for this are millimetres of mercury (mmHg) because old-fashioned blood pressure machines measured the pressure according to the height of a column of mercury – like in a thermometer.

The systolic number is normally over 100 and the diastolic number is normally less than 100. The systolic pressure is higher because it represents the highest pressure in the arteries, which is generated when the heart is squeezing to pump blood around the body. The diastolic number represents the lowest pressure in the arteries, when the heart is completely relaxed and full of blood.

High blood pressure – called hypertension by doctors – is a very common problem, but it isn’t something that you can necessarily feel or notice. Extremely high blood pressure can cause symptoms, such as headaches or blurred vision, but this is very much the exception. Indeed, it is estimated that as many as 7 million people in the UK could be living with high blood pressure without knowing it. It is therefore really important to have your blood pressure checked so that you can understand if you are at risk of the problems associated with having high blood pressure in the long-term.

We think that most of the risk from high blood pressure in otherwise healthy people comes from having a blood pressure consistently higher than 140/90mmHg. People with values routinely higher than this are at an increased risk of developing heart failure or having a heart attack or a stroke in the future. In people with other medical problems – especially those with diabetes – doctors suggest that people should aim for blood pressures lower than 130/80.

Lots of things determine what your blood pressure is. Everyone is different and there is no one explanation for why some people have high blood pressure and other people don’t. Knowing that other people in your family have had high blood pressure makes it more likely that you could have it too, and is a good reason to go and get it checked.

We know that there are some common things which people can change about their lifestyles which can help lower the blood pressure. These include:

  • Regular exercise
  • Maintaining a healthy weight
  • Reducing salt in your diet
  • Not drinking too much alcohol

Even with these measures some people may be advised to start on medication to bring their blood pressure down to protect them against heart disease and strokes in the future. Your doctor can help you make decisions about whether that is the right thing for you.

Some people always have very high blood pressure when it is checked by a doctor or a nurse. Repeated measurements will demonstrate that a certain number of these people only have high blood pressure because it is being checked. This is called ‘white coat syndrome’ and can be tricky to diagnose. Your doctor may recommend a 24 hour blood pressure monitor to try and work this out.

Some people may be told that they have low blood pressure. This is unlikely to be a problem unless you have symptoms of dizziness or blackouts. If you feel well then don’t worry if someone says your blood pressure is low – it is probably just normal for you. Common reasons for having low blood pressure are:

  • Dehydration
  • Medication use
  • Acute illness
  • Chronic heart failure

If you are worried about low blood pressure be sure to talk to your doctor before stopping any medicines that are prescribed for you.''


Dr Paul M Haydock MBBS, MA(Cantab.), MD(Res), MRCP

Consultant Cardiologist


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