Blood pressure (BP) varies with every heartbeat and in response to stimuli such as exercise, emotion, and physical activity.
There are various ways to measure blood pressure during daily life. The techniques used can be invasive or non-invasive, continuous or intermittent.
Early research studies measured BP beat-to-beat during daily life with devices which were invasive – with a plastic tube in the artery at the elbow – and a fluid pump to keep it from clotting. We still use invasive monitoring in ICU and Critical Care Units but not as an ambulatory test. Invasive measurements are used in patients confined to a hospital bed and measure blood pressure continuously.
A non invasive device to measure blood pressure continuously (Finapres or Portapres) is available but is a research tool not used widely in clinical practice.
Non invasive, intermittent BP measurement during daily life – ambulatory BP – is readily available & widely used.
Nowadays we use a non-invasive technique with a standard sized BP cuff placed on the upper arm and connected by tubing to a small pump which records BP intermittently during normal daily life over 24 hours. These devices are much more accurate and reproducible than the standard home BP monitors. The devices are small, sophisticated, battery operated and lightweight. The number of measurements varies but may be up to 72 in 24 hrs.
We can diagnose high blood pressure (hypertension) more accurately, so that patients whose BP is actually normal are not treated unnecessarily (‘white coat hypertension’). It is the best way of looking at the effects of lifestyle changes, drug treatment and newer treatments such as renal artery denervation. The long term effects of hypertension are better predicted by 24hr BP monitoring. These devices can also detect unusual BP patterns such as ‘non-dippers’ whose BP does not fall at night. Such patterns are more common in complicated BP patients such as those with kidney failure, heart failure and hypertension of pregnancy (’pre-eclampsia’)
Download Patient Information Sheet for this test here.
Frequent self-measurements of BP using simple home BP recorders which you can purchase from a pharmacy can be a very good alternative to Ambulatory BP testing. But these home devices are much less sophisticated than ABP machines and tend to be less accurate, more so for diastolic than systolic BP.
The patient measures their BP at set times of the day over several days, typically at least a week, and records the average of the systolic (highest) and diastolic (lowest) readings. The average can be obtained by recording the information in a spread sheet program which can calculate it. Some devices automatically record and average the readings taken.
Simple computer programs such as iPad or Android apps are increasingly used to record BP measurements on phones or tablet computers. There are also devices which connect directly to a smart phone or tablet computer (withings.com)