Measuring your own blood pressure

High Blood Pressure or 'Hypertension' is a very common medical condition that in many cases is completely 'silent' - hence the term 'silent killer'.  It is one of the commonest risk factors linked to stroke as well as heart failure in later life, and it is thought to affect up to 1 in 4 people over 50 years of age.

The medical professional acknowledges the fact that in one half of all cases of hypertension it is either undiagnosed or it is poorly controlled which makes Hypertension one of the largest public health issues in developed countries.

Hypertension can be therefore be regarded as one of the largest single most important causes of preventable heart disease and stroke.

To make matters more difficult, many people are affected by  ‘white coat’ hypertension, meaning that the blood pressure (BP) recordings in clinic are higher than the recordings measured at home, so it can be difficult for their physician to know whether the blood pressure is 'high', 'low' or 'adequately controlled'.

It is for this reason that many physicians will recommend that anyone at risk of hypertension should simply measure it for themself.

Obtaining your own BP machine

Your GP Surgery may have a device you can borrow. For those people who need to make regular measurements it may well be worth purchasing your own relatively inexpensive device. There are hundred of models to choose from, but a good model can usually be obtained from your local chemist or online store. Not all are the same in terms of accuracy, so it might be wise to buy one that has been tested and approved by the British Hypertension Society

Follow our Instructions narrated by Anthea Turner

 

My BP measurements are all different, which one is correct?

Nobody has a static Blood Pressure; it varies like a car's engine speed, depending on what it/you are doing and how much adrenaline and stress hormone is being released; it is therefore somewhat pointless to measure your blood pressure when stressed, aggrevated or during exercise.

In addition we all have a natural circadian variation or rhythm in our blood pressure - which describes the phenomenon whereby  a natural fall in BP occurs during the night/ afternoon and a rise as part of the 'wake up call'  starting shortly before rising in the morning.

This means that if you average morning and evening recordings you may well be under-estimating your true blood pressure.

Tip: Download and print our Patient Information sheet, which reiterates NICE guidance, which is to assess your BP at rest, usually first thing in the morning when first rising and (perhaps) last thing at night.  For those people who enjoy a morning cup of tea or hot drink, why not put the kettle on and while it boils, sit at the kitchen table so that you are always at the same height in relation to the monitor, then measure it three times. Repeat each day for a week and then, if it is satisfactory put the thing away for 12 weeks!

Averaging results

Home Blood Pressure monitors are not quite as accurate as human measurement. This factor introduces a variation in measurement, or error which, when added to natural day to day variation and diurnal variation can make it hard to know which value to believe.

This problem can be got around using the law of averages - or more technically regression to the mean.

It is very important this is done correctly, variations that I have heard of which are NOT Correct include:

  1. Taking the BP several times and taking the lowest value!
  2. Measuring the BP at various points of the day and averaging them all- because the BP naturally drops in most people during the day the average may produce a false sense of security.
  3. Measuring BP when active, stressed or ill. The BP that needs to be measured is the resting or basal BP- not what it goes to when ill or stressed.

The correct method is to average several recordings taken a few minutes apart, and then repeat each day of the week at the same time, so that machine measurement errors and natural variation are averaged out.  In most people the morning average will be higher than the evening recordings, so should be then focussed on- since if you get the morning average below 135/85 mmHg and have no side effects from low BP at other times, you have succeeded.

Our spreadsheet (which performs the calculation for you) or form that helps you to calculate the average is quite helpful and can be shown or sent to your Physician.

Related Stories and links

Download Blood Pressure Spreadsheet
Download Blood pressure Form 
Roger Taylor, Anthea Turner and Peter Alliss Launch Stroke Prevention DVD
Reducing Salt to lower your blood pressure
NICE press release 2012Update Blog Entry
British Hypertension Society
Home BP Measurement - Patient information Leaflet
What is the 'best' blood Pressure?
Other things you can do to reduce your risk of stroke
Stroke prevention: Helping yourself
Why do I need to take so many tablets to control it?



Written by

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Edward Leatham is a Consultant Cardiologist in Surrey and a Trustee of Haste and Haste Academy.

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