Thursday, 30 October 2014
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Monitor offers more accurate blood-pressure readings

Scientists have unveiled a new, more accurate blood-pressure monitor that calculates the flow close to the heart.

The wrist-mounted device, developed at Leicester University, uses computer modelling to convert readings taken at the arm to a measurement of blood pressure in the aorta, the body’s main artery.

Doctors hope the technology will better identify patients with high central aortic systolic pressure (CASP) because readings at the wrist can be significantly different from those at the heart, especially for young people.

Being able to measure blood pressure in the aorta is also important because it is closer to the heart and brain where hypertension can cause damage.

‘It is difficult to argue against the proposition that the pressure near to your heart and brain is likely to be more relevant to your risk of stroke and heart disease than the pressure in your arm,’ said research team leader Prof Bryan Williams.

‘It is not going to replace what we do overnight, but it is a big advance. Further work will define whether such measurements are preferred for everybody or whether there is a more defined role in selective cases to better decide who needs treatment.’

The blood pressure in large vessels close to the heart is lower than in the arm because of the amplification of the pressure wave as it moves away from the heart.

This amplification can change with ageing, blood-vessel disease and medication, meaning that routine measurements of blood pressure at the arm are not a good predictor of the pressure near the heart.

The amplification is also greater in younger people with healthy arteries, meaning some people can appear to have high blood pressure based on readings at the arm, when their aortic pressure is normal.

The new device records a pulse wave and measures the blood pressure at the wrist at the same time and then uses mathematical modelling to filter out the amplified portion of the pulse wave to reveal the CASP.

The Leicester team collaborated with Singapore-based medical technology company HealthSTATS International, which developed a simple wrist-strap device that uses a skin contact sensor to record the pulse wave.

Combined with a traditional blood-pressure monitoring cuff, the device then calculates the CASP within a few minutes.

Dr Choon Meng Ting, chairman and chief executive officer of HealthSTATS, said: ’It will empower doctors and their patients to monitor their central aortic systolic pressure easily, even in their homes, and modify the course of treatment for blood-pressure-related ailments.

‘Pharmaceutical companies can also use CASP devices for clinical trials and drug therapy. All these will ultimately bring about more cost savings for patients, reduce the incidences of stroke and heart attacks and save more lives.’

The government’s National Institute for Health Research (NIHR) invested £3.4m in the project, while the Department of Health provided £2.2m capital funding to establish a Biomedical Research Unit at Glenfield Hospital in Leicester.


Readers' comments (5)

  • It would be better to measure the pulse train on the carotid and thus circumvent the variables thrown up by measuring BP on the arm or wrist.

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  • Might be hard to get people to wear a collar though :D The risk of a band around your arm might be less than the risk of one around your neck.

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  • I have doubts about / great admiration for the mathematics which can cope with pressure wave magnification in a curving, branching system of varying elasticity and cross-sectional area and shape, driven by a pump of varying stroke volume and oscillation rate.
    In the end the doctor does not actually need to know the absolute value of the large vessel pressures, so much as the epidemiological implications of the pressures he/she can and does measure.
    We (I write as a retired GP) had to resist the onslaught of science pushing for blood pressure to be measured in kPa, after a century and a half of "mmHg" when there is never a need to convert and interact with the "real world" that uses kPa.
    Similarly here, a blood pressure of 130/80 has epidemiological implications, which vary with age, but are understood.
    Many current fundamental technologies were derided at the outset, so this must be allowed to flourish, but needs to run alongside established practice for a long time, before its (currently expensive and complex) devices replace the the simple consulting room kit + brain.

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  • Taylor's constant
    ==========

    Re-reading my earlier post prompted the generation of a theorem:

    Dc x Mb = T

    where Dc = device complexity
    Mb = medical brainpower
    and T = Taylor's constant

    This explains the (observed) phenomenon that the outcome (represented by T) is unchanged; as Dc rises, so Mb falls, to maintain this equilibrium.
    Explanations vary as to the prime mover in this system - whether Dc has to rise to meet a falling Mb (blame MMT {Modern Medical Training} for this) or whether Mb falls as a consequence of reliance on an increasing (and fashionable) Dc.

    I wish this were a joke, but there are real world examples of clinical acumen being lost as better imaging and algorithm-assisted diagnosis nudge bedside expertise, keen observation and perceptiveness out of mainstream medical activity.

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  • Alas, Dr Taylor, you are so right.

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