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Last Updated: Sunday, 8 August, 2004, 23:20 GMT 00:20 UK
War plane test can check arteries
Image of Mr Calvert with a duplicate aneurysm
Mr Calvert is holding a model of an aneurysm
A wartime test used to gauge stress on the superchargers of Spitfire planes can monitor stress on the body's main artery, researchers have shown.

This could help surgeons assess how much pressure they can safely put on the body's main artery the aorta, says the University of Warwick team.

The test works out stress levels by looking at patterns of coloured light reflected from an object's surface.

The team worked with a UK heart surgeon to adapt the test.

Photoelasticity is a technique that has been used since the 1930s in industry to look at stress levels.

Stress test

Modern devices use high tech light sources and computer analysis to get an even more precise idea of the stresses involved.

Mr Geoff Calvert from Warwick University's manufacturing group, along with heart surgeon Dr Arindam Chaudhuri at University College London, set out to see whether this technique could be used to model the stress that surgical procedures would put on blood vessels.

This is particularly important in aneurysm surgery, where the blood vessel has a dangerous bulge that needs to be repaired before the pressure inside the vessel becomes too great and it bursts.

If an aneurysm in the aorta bursts it can be fatal because this is the vital vessel that carries all of the blood from the heart to the body.

Previously, surgeons have tried placing mechanical strain gauges on an aortic aneurysm as they manipulated it but found the gauges themselves placed unwanted additional physical strain on the aneurysm.

Mr Calvert and Dr Chaudhuri instead took a 3D scan of a patient's aneurysm to make an exact copy out of latex.

I do see a huge practical use, if it works, for it in predicting whether an individual is at high risk of rupture
Consultant vascular surgeon Mr Mark Whiteley

They then covered this latex copy with a reflective covering and used photoelastic stress analysis to examine the stress on the model aneurysm as the surgeon manipulated it.

This can help surgeons work out the safest way to correct the defect, say the researchers.

Mr Calvert explained: "What we have got is a stress plot of where high stress areas are likely to be and where potential problems can occur with bursting of the aneurysm.

"And, more importantly, when the surgeons put the stent pipe in, which actually bridges the aneurysm and repairs it, how far up the artery you need to continue that stent in order to avoid stress concentration and make the stent a long term good repair so there's no risk to the patient," he said.

Dr Chaudhuri said: "It will actually allow surgeons to explore a greater range of possible interventions and manipulations of an aneurysm and get a clear picture of the stresses created without the obvious risks that testing less conservative interventions would bring if they were tried out on the actual patient."

The researchers hope they will soon be able to carry out tests on human tissue inside living patients without having to make a model.

Future hopes

Mr Calvert said: "You may not need the model. You would just need the light source and the camera."

He has been working with other researchers at the University using the same technology for looking directly at eye conditions like glaucoma, where there is increased pressure in the eye, without having to use a model.

"It's at a very early stage. But we have done some early trials and it looks promising. It could be a way of measuring pressure in the eye in a completely non-invasive way."

Mr Mark Whiteley, consultant vascular surgeon in Guildford, said it might have potential for identifying which patients should be operated on early.

"Some aneurysms grow very big before they rupture, some rupture when they are very small. We do not know which of our patients with small aneurysms are at risk.

"I do see a huge practical use, if it works, for it in predicting whether an individual is at high risk of rupture.

"If we can actually correlate a certain configuration with stress and rupture we might well be able to predict which aneurysms are most at risk of rupture and then fast track them through to surgery," he said.

The researchers will present their findings at a meeting of the British Society for Strain Measurement and are seeking funding to continue their research.


SEE ALSO:
Doctors hail heart defect test
07 May 04  |  Gloucestershire
Aneurysm screening possible
13 Jul 03  |  Health


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