Blood pressure measured with breakthrough technology

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Blood pressure measured with breakthrough technology

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Engineers Edge - In a major scientific breakthrough, a new blood pressure measurement device is set to revolutionise the way patients' blood pressure is measured.

The new approach, invented by scientists at the University of Leicester and in Singapore, has the potential to enable doctors to treat their patients more effectively because it gives a more accurate reading than the current method used. It does this by measuring the pressure close to the heart – the central aortic systolic pressure or CASP.

Blood pressure is currently measured in the arm because it is convenient however this may not always accurately reflect what the pressure is in the larger arteries close to the heart.

The new technology uses a sensor on the wrist to record the pulse wave and then, using computerised mathematical modelling of the pulse wave, scientists are able to accurately read the pressure close to the heart. Patients who have tested the new device found it easier and more comfortable, as it can be worn like a watch.

Being able to measure blood pressure in the aorta which is closer to the heart and brain is important because this is where high blood pressure can cause damage. In addition, the pressure in the aorta can be quite different from that traditionally measured in the arm. The new technology will hopefully lead to better identification of those who will most likely benefit from treatment by identifying those who have a high central aortic systolic pressure value. This will be especially important for younger people in whom the pressure measured in the arm can sometimes be quite exaggerated compared to the pressure in the aorta.

A key question is whether measurement of central aortic pressure will become routine in clinical practice. Professor Williams said: "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 and who doesn't and whether the treatment is working optimally"

The University's close collaboration with the Singapore-based medical device company HealthSTATS International ("HealthSTATS") has led to the development of this world-first technique for more accurate blood pressure measurement.

The research work carried out by the University of Leicester was funded by the Department of Health's National Institute for Health Research (NIHR). The NIHR has invested £3.4million with a further £2.2million Capital funding from the Department of Health to establish a Biomedical Research Unit at Glenfield Hospital, Leicester, dedicated to translational research in cardiovascular research. The work, led by Professor Bryan Williams, Professor of Medicine at the University of Leicester and consultant physician at University Hospitals of Leicester NHS Trust, has the promise to change the way we measure blood pressure.

Professor Williams, who is based in the University of Leicester's Department of Cardiovascular Sciences at Glenfield Hospital, said: "I am under no illusion about the magnitude of the change this technique will bring about. It has been a fabulous scientific adventure to get to this point and it will change the way blood pressure has been monitored for more than a century. The beauty of all of this, is that 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.

"Leicester is one of the UK's leading centres for cardiovascular research and is founded on the close working relationship between the University and the Hospitals which allows us to translate scientific research into patient care more efficiently. Key to our contribution to this work has been the support from the NIHR without which we would not have been able to contribute to this tremendous advance. The support of the NIHR has been invaluable in backing us to take this project from an idea to the bedside. Critical to the success of this project has been the synergies of combining clinical academic work here with HealthSTATS and their outstanding medical technology platform in Singapore. This has been the game-changer and I really do think this is going to change clinical practice."

Dr. Choon Meng Ting the Chairman and CEO of HealthSTATS said: "This study has resulted in a very significant translational impact worldwide as 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 BP-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."

Health Secretary Andrew Lansley said:

"I saw this new technique in action in Leicester when I visited a few months ago. This is a great example of how research breakthroughs and innovation can make a real difference to patients' lives. We want the NHS to become one of the leading healthcare systems in the world and our financial commitment to the National Institute for Health Research reflects this.

"I believe patients deserve the best treatments available and science research like this helps us move closer to making that happen."

Professor Dame Sally Davies, Director General of Research and Development and Interim Chief Medical Officer at the Department of Health, said:

"This is fantastic work by Professor Williams and his team and I am delighted to welcome these findings. I am particularly pleased that the clinical research took place at the NIHR Biomedical Research Unit in Leicester. NIHR funding for Biomedical Research Centres and Units across England supports precisely this type of translational research, aimed at pulling-through exciting scientific discoveries into benefits for patients and the NHS by contributing to improved diagnostics and treatments."

Notes:

1. Results from the research have been published in the Journal of the American College of Cardiology. The research publication describes a novel method to measure aortic pressure non-invasively. The study reports that using this approach, central aortic systolic pressure can be measured non-invasively with an accuracy of 99% when compared to the pressure measured by inserting a catheter directly into the aorta close to the heart during a cardiac catheter procedure. The Singapore based medical devices company HealthSTATS has embedded this new and validated method into a range of blood pressure measurement devices that are enabled to measure central aortic systolic pressure (CASP), namely A-PULSE CASP®, CASPro® and CASPal®, which are designed for hospital, clinical and home use respectively. All three medical devices have attained the FDA 510(k) listing and CE (MDD) Mark. For the purpose of this research, the A-PULSE CASP® was used.

2. Professor Williams, is an NIHR Senior Investigator led the work in close collaboration with Dr. Ting and team from HealthSTATS in Singapore. Dr Ting, and his team have worked with Professor Williams and Dr. Peter Lacy in Leicester for over 4 years on this project. In that time, the idea has gone from concept into production of new clinical devices.

3. About the Research team in Leicester: Professor Bryan Williams is Professor of Medicine at the University of Leicester and Consultant Physician at the University Hospitals of Leicester NHS Trust. Professor Williams is also an NIHR Senior Investigator and conducts his research at the NIHR-funded Biomedical Research Unit in Cardiovascular Diseases in Leicester. Professor Williams has led research into central aortic pressure and with Dr Ting, the development of the novel method for its measurement.

About the NIHR

The National Institute for Health Research provides the framework through which the research staff and research infrastructure of the NHS in England is positioned, maintained and managed as a national research facility. The NIHR provides the NHS with the support and infrastructure it needs to conduct first-class research funded by the Government and its partners alongside high-quality patient care, education and training. Its aim is to support outstanding individuals (both leaders and collaborators), working in world class facilities (both NHS and university), conducting leading edge research focused on the needs of patients.

About HealthSTATS International :

Based in Singapore and founded in 2000, HealthSTATS International Pte Ltd is a bio-monitoring medical device company dedicated to technology research and product development of innovative medical devices to provide doctors with an evidence-based approach to monitoring and management of hypertension. The Company's proprietary EVBP® technology was developed by a multi-disciplinary team, in collaboration with several institutions like Nanyang Technological University, National University Hospital and the National Heart Centre. The ground-breaking EVBP technology is highly versatile and has a multitude of clinical applications, which include ambulatory blood pressure monitoring (ABPM) and continuous non-invasive blood pressure (CNIBP) monitoring, as well as Pulse Waveform analysis (PWA). In December 2006, HealthSTATS was conferred the Technology Pioneer 2007 status by the World Economic Forum in its Technology Pioneers 2007 programme, under the Biotechnology & Health category.

BACKGROUND Q&A

ABOUT BLOOD PRESSURE:

When the heart beats it generates a pressure in the arteries to pump blood around the body. In some people, the pressure generated is too high and this is called high blood pressure or hypertension. High blood pressure is a major risk factor for strokes, heart disease and premature death. It is also linked to an increased risk of kidney disease and dementia. High blood pressure becomes much more common as people age. In the UK high blood pressure affects about 1 in 4 adults and 1 in 2 over the age of 65 years. In most cases, no underlying cause is identified but it is common for relatives of those affected to also have had a high blood pressure. High blood pressure has been called the "silent killer" because it usually causes no symptoms and can only be detected by measurement of blood pressure. This is why blood pressure measurement is commonly undertaken when people visit their doctor. The treatment of high blood pressure involves a combination of lifestyle changes and medicines. Lifestyle changes that have been shown to reduce blood pressure include regular exercise and maintaining an ideal body weight, eating a healthy diet and reducing salt intake and avoiding excessive alcohol consumption. Most people eventually need medication to lower their blood pressure and there is very good evidence from many clinical studies that treating high blood pressure reduces the risk of developing strokes and heart disease. The NHS spends over £1 billion per year on medications to treat high blood pressure and analyses by NICE has shown this to be highly cost-effective.

Measuring Blood pressure: The standard way to diagnose high blood pressure is to inflate a cuff around the upper arm. When the cuff pressure exceeds the pressure of the blood in the arteries, the flow of blood in the arteries of the arm is temporarily interrupted. As the cuff deflates, the flow of blood is restored and this can be detected by listening over the arteries with a stethoscope or by automated devices attached to the cuff. This gives two readings, the highest pressure called "systolic pressure" which is the peak pressure in the arteries when the heart pumps and the lowest pressure "diastolic pressure" which is the pressure in the arteries when the heart is between beats. This is usually written as a value such a 120/80 where the higher number is the systolic pressure and the lower the diastolic pressure. A truly normal pressure when measured in the arm in this way is less than 120/80. High blood pressure is diagnosed when the systolic pressure is above 140 or the diastolic pressure is above 90. Blood pressure is quite variable so the diagnosis of high blood pressure is only made when repeated readings, usually on two or more visits to the doctor, confirm that a person's blood pressure is consistently elevated.

Why is the pressure close to the heart, i.e. in the central aortic pressure, different from the pressure that is measured in the arm using a conventional blood pressure device?

It has been known for a long time that the pressure in the large vessels close to the heart (e.g. the aorta) is lower than the corresponding pressure on the arm. This may seem surprising but it is due to amplification of the pressure wave as it moves away from the heart to the arm. If this amplification was fixed, then measuring pressure in the arm would always be a good measure of pressure in the aorta – but it is not fixed. The amplification of the pressure wave as it moves from the heart to the arm can vary with ageing, disease of the blood vessels and with medication. This means that the pressure we measure routinely in the arm is not always a good predictor of the pressure in the large arteries which we call central aortic pressure. This is important because the central aortic pressure is the true pressure that the heart, the brain and other major organs actually sees and as such, is likely to be a better indicator of the pressure that can cause damage if it is too high. Another interesting aspect of this pressure amplification is that it is paradoxically greater in younger people with healthy arteries. This means that some people with a high blood pressure when measured in their arm may actually have a completely normal central aortic pressure. This amplification effect is greatest for systolic pressure and can result in a difference between central systolic aortic pressure and systolic pressure in the arm as great as 30mmHg. So the only way to really know what the central aortic pressure is, is to actually measure it in some way.

Is it known whether central aortic pressure is a better predictor of clinical outcomes than conventional blood pressure measurement?

Central aortic pressure has not been measured as often as pressure in the arm for obvious reasons. Whenever the two different measurements have been made in patients, central aortic pressure appears to be a stronger predictor of risk of damage to the heart, blood vessels and the kidneys and also a better predictor of clinical outcomes but more studies are needed in this area. This simple and inexpensive technology will allow this to happen. In fact such studies are already underway.

How does this new method work?

We needed a way to eliminate the amplification that increases the pressure in the arm so that we could get back to the original central aortic pressure. To do this we used mathematical modelling, similar to the kind of modelling that is undertaken to remove distortion of waves in many other applications. The process acts like a filter, filtering out the amplified portion of the pulse wave to reveal the central aortic pressure. We had to do a lot of validation studies, including measurements of the actual pressure in the central aorta near the heart in volunteer patients who were already undergoing a procedure to investigate their heart known as cardiac catheterisation. We showed that our new method produce almost identical central aortic pressures to those being measured directly in the heart, confirming that this method works very well.

A key element of the breakthrough is incorporation of this novel method to measure central aortic pressure into a simple device that would make this practical and feasible to use in clinical practice. Thus, this work is founded on a scientific discovery and direct application to new technology. The collaboration involved close working on all aspects of the project, between clinical scientists at the University of Leicester led by Professor Bryan Williams and a bio-monitoring medical device company in Singapore (HealthSTATS), led by Executive Chairman and CEO Dr Choon Meng Ting.

To make the measurement of central aortic pressure, it is necessary to record a pulse wave at the wrist at the same time as blood pressure is measured in the arm. It is the mathematical computation of information in the pulse wave that allows the measurement of central aortic pressure. Dr Ting had invented a simple wrist strap device that incorporated a sensor that sits on the skin overlying the wrist and records the pulse wave, in the same way as you can easily feel your pulse at the wrist. The information in that pulse wave is instantaneously computed by the new method we have discovered to accurately derive central aortic pressure. The measurement process takes only a few minutes longer than normal blood pressure measurement and is completely non-invasive.

The device looks like a normal blood pressure monitor, with one important difference. There is an additional strap attached to the monitor that is placed around the wrist. This contains the sensor that captures the pulse wave. Once the blood pressure cuff and wrist strap are in place – a button is pressed which blows up the cuff like a normal blood pressure measurement, but also captures the pulse wave at the wrist. The device contains the programme that we developed that uses the blood pressure and the pulse wave form to derive central aortic pressure. The pulse sensor has also been incorporated into the strap of a wrist watch that allows ambulatory measurements of blood pressure to be recorded day and night.

Will doctors soon be using this new technology to routinely measure blood pressure?

The technology is now available and ready to use. However, it is not quite ready for it to replace the standard methods of measuring blood pressure. It will take some time to gather all of the information needed to better define the normal values for central aortic pressures and its predictive value for clinical outcomes. However, having this new method and its incorporation into easy to use technology has brought the science much closer to the patient and in the view of the research team, "it will not be long before central aortic pressure enters routine clinical practice". But don't expect your doctor to be able to measure it for you today.

Professor Williams notes; "the beauty of all of this, is that 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!"

Image: Professor Bryan Williams (center) and Health Minister Andrew Lansley (right) with Ph.D. student Daniel Timms (left) are at the opening of the University of Leicester Cardiovascular Biomedical Research Unit. Credit: University of Leicester.

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