Off the cuff: a revolutionary new blood pressure monitoring device
For more than a hundred years, blood pressure has been measured in largely the same way. You’ve probably experienced it yourself: your doctor will inflate a cuff around your upper arm, temporarily interrupting the flood of blood in your brachial artery. From this, they will take a reading of the pressure when your heart beats (systolic pressure) and when it is between beats (diastolic pressure) – which is why blood pressure (BP) is given as ‘this number over that number’.
But this is not ideal because blood pressure is amplified as it travels away from the heart. Being able to measure blood pressure near the heart, specifically in the aorta – called ‘central aortic systolic pressure’ or CASP - is important because this is where high blood pressure can cause damage. But obviously your aorta is much harder to reach than your upper arm, what with that whole rib cage and so on. It can be done - but only using a surgical procedure.
Clearly what is needed is some way to measure CASP indirectly using blood vessels we can actually get at. Now, if the relationship between brachial BP and CASP was constant, there would be no problem – you could just use a multiplication factor. But the ratio between the two measurements varies not only between individuals but also within each person as they get older and their artery walls become stiffer.
A wristwatch from Singapore
The new approach, developed by scientists at the University of Leicester, uses technology invented by Singapore-based medical device company HealthSTATS International: a device worn on the wrist which can accurately record a patient’s pulse. Not just the pulse rate but the actual pulse wave.
Professor Bryan Williams from our Department of Cardiovascular Sciences is part of the team at the Leicester Cardiovascular Biomedical Research Unit (BRU), a collaboration between the University of Leicester and University Hospitals of Leicester NHS Trust. Based at Glenfield Hospital, the BRU was opened last year by Health Minister Andrew Lansley. When Professor Williams was in Singapore a few years ago he came across the HealthSTATS device and realised that this might be the missing piece of the blood pressure puzzle.
In short, your pulse wave provides enough data to be able to determine your aortic blood pressure from a measurement of your brachial blood pressure – without having to cut you up or poke anything into you. The non-invasive procedure uses a device which not only looks like a wristwatch and is worn like a wristwatch but, in some versions, actually is a wristwatch. A carefully positioned pad presses on the radial artery on the inside of your wrist; it’s a bit tight but not uncomfortable. Wearing this device for 24 hours provides an average which flattens out pulse-raising factors such as excitement or exercise.
Working with colleagues from HealthSTATS, the Leicester researchers have built up an extensive collection of patient data from which they have derived an effective algorithm for calculating CASP. Direct comparison with traditional CASP measurements obtained using the old-fashioned, invasive method shows a 99% correlation. The results of all this research have now been published in the prestigious Journal of the American College of Cardiology.
The future of blood pressure measurement
It is worth stressing that the new system is not designed to replace the old inflatable cuff that we all know and love; you need the cuff and the wristwatch to calculate CASP (although you don’t need to wear the cuff for 24 hours). What it will do is let doctors measure CASP much more easily; you could potentially have your aortic blood pressure measured by your GP.
The importance of all this is that brachial BP can be unreliable, especially in young people whose more flexible blood vessel walls can give misleadingly high blood pressure, leading to unnecessary medical interventions. Conversely, old people with stiffer blood vessels may give a misleadingly low reading of brachial BP, disguising dangerous high blood pressure which can be a precursor to heart attack or stroke.
It may be some time before this technology reaches the majority of patients but the scientists hope that you see it soon because you’ll be helping them determine whether CASP really can become the standard measurement for blood pressure. And that could save lives.
How you can help our research
This development was borne from the internationally renowned expertise in our Department of Cardiovascular Sciences, where life-changing and life-saving research goes on every day. The University of Leicester has recently launched an urgent appeal to raise £4 million to complete a £12.6 million Cardiovascular Research Centre at the Glenfield Hospital to provide our researchers with the labs and equipment to keep doing that. Please take a look at the short video about the Cardiovascular Research Centre Appeal on our Alumni and Supporters site, where you can find out how you can help make it a reality.