Uncovering the mechanisms of high blood pressure

Hypertension

Researchers at King’s College London have found a new procedure to diagnose high blood pressure, as recently reported in the journal Hypertension. These findings could help reduce NHS spending on drugs as well as reducing the number of GP visits. The NHS currently spends over £8bn per year on drugs, and a large portion of this is blood pressure lowering drugs.

Cardiovascular disease is the number one cause of death globally: more people die annually from problems with their heart and blood vessels than from any other single cause. Most of these people suffer from high blood pressure, or hypertension. Around 30% of people in England have hypertension but many don’t know it. If left untreated, high blood pressure increases your risk of a heart attack or stroke. The main way of knowing there is a problem is to have your blood pressure measured.

The traditional understanding of hypertension is that is it caused by hyper-constricted muscles surrounding arteries increasing the resistance to flow, pushing blood pressure up. Many hypertension drugs target these muscles, relaxing them to decrease resistance and therefore blood pressure. The most common way to diagnose hypertension is using a cuff on your arm. However this is not completely reliable due to errors from devices we used to measure blood pressure, as well as hypertension masked as normal blood pressure variation. For example if you have cup of coffee or run up some stairs your blood pressure will rise temporarily but will return to your normal resting pressure.

More recently, the contribution from the stiffness of the artery wall has been shown that it perhaps more important impact upon blood pressure.  Pulse wave velocity (PWV) is the measure of the speed at which a pulse travels down the arteries every time the heart beats, and indicates stiffness. There are draw backs with PWV measurement too.  It too varies with varying blood pressure, meaning that this practice hasn’t been picked up by clinicians.

They set out to change the way aortic stiffness is measured such that there is no confounding effects of blood pressure.  While using a pressure sensor on the fingertip and one in a mouthpiece, they measured the PWV variations every heartbeat while subjects perform breathing manoeuvres. From this, they were able to obtain to characterise an individual’s arterial stiffness over a wide range of pressures upon the aorta wall.  Thus they were able to obtain a more complete assessment of the health of the arteries, and discern an individual with truly stiff arteries from a healthy individual, regardless of blood pressure confounding the measurement.

Professor Phil Chowienczyk, Professor of Cardiovascular Clinical Pharmacology who is leading on this study said “We know that there is room for improvement in the diagnosis and treatment of hypertension and this needs to start with a better understanding of what causes high blood pressure, and how to distinguish individuals at risk from those who are not.”

There has been continuing debate to whether the apparent increased stiffness in patients with hypertension is due to increased blood pressure stretching the aorta, making it appear stiff; or whether there has actually been a structural change.

These findings show that they can obtain an individual specific measure of arterial stiffness, and therefore cardiovascular risk. They also showed that arterial stiffening is a result of a structural change of the aorta wall, rather than just higher pressure making the aorta appear stiffer.

Dr Nicholas Gaddum, Clinical Research Fellow in the Division of Imaging Science & Biomedical Engineering at King’s College London added “We need to know if any drugs are truly assisting those who have stiffer aortas, and if not use a measure such as that used in our study to develop effective treatment.”

This research has the potential to reduce the burden on national health costs, improve the early detection of arterial disease in patients, and allow us to assess and develop drugs which focus on aortic stiffness.

Preliminary research was funded by the MRC. The EPSRC are funding the development of this work into a more comprehensive analysis of cardiovascular disease whereby patients can have a personalised assessment of what is causing their high blood pressure.

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