Smart clothes check your heart

With electrodes sewn into your clothes, it will be simple to
check that your heart is working as it should. “As the population gets older, we are going to need to measure more things at home,” says Linda Rattfält, who has just earned her doctorate in Physiological Metrology.

Imagine smart wristlets, or a girdle around your waist, that can send information about your pulse directly to the health care clinic to check if your heart is working as it should, for example after a heart attack.

“There are smart clothes for sports applications, but the smart textiles I’m working with must be both extremely dependable and so simple that they can be used and managed at home without needing medical training,” Dr Rattfält, of the Linköping University Department of Biomedical Engineering, tells us.

She is researching “smartware”, or intelligent textiles, conductive yarn and fabrics where electrode materials are woven into the fabrics or spun into the yarn. The goal is to find a sufficiently simple and dependable technology that makes it possible to safely manage a larger part of health care at home without trained personnel.

To transport data rather than people, as Dr Rattfält puts it.

Different types of electrodes

“This is not about technology for continual monitorin - then perhaps people shouldn’t perhaps be tended to at home – but for running regular check-ups, like putting yourself on the scale at regular intervals,” Dr Rattfält says.Linda RattfältFoto: Monica Westman

She has studied several different types of electrodes and compared them with electrodes that are put on the body when an EKG is conducted as part of treatment. She has studied both textile electrodes, developed at the Swedish School of Textiles in Borås and which are used in protective clothing, for example, and also specially designed electrodes made from printed electronics from Acreo in Norrköping.

“The innovative thing about our work, really, is that we are combining electrodes with printed electronics; the printed electronics are also more stable and the variation in performance is not that great.”

There are many technical challenges to this: the electrode cannot be stuck to the body; it also needs to tolerate sweat; and the signal cannot be affected to greatly; the point is to be able to take measurements during movement. They may perhaps want to see how a heart responds to exertion – a walk up a hill or up a flight of stairs - and if the pulse increases as it should.

“Since we want to measure small differences in potential, it’s also a matter of finding good, sensitive amplifiers and this requires proper signal processing,” Dr Rattfält argues.

Variations in the heart´s rhythm

The amplifier used was specially developed for research purposes by Bengt Ragnemalm, research engineer at the Department of Biomedical Engineering. And one-half of Dr Rattfält’s thesis deals with methods for finding out which out of all the body’s signals is the one coming from the heart.

“We want to see variations in the heart’s rhythm and don’t need any precise EKG curves, but I’ve looked at two different methods for signal processing and both work pretty well,” she says.

But the one method records all the body’s signals, and statistical methods are then used to separate one signal from another. With the other method, you look for an expected signal; when the system finds it, the position is marked with a weight, the size of which depends on how similar the signal is to the one expected.

Dr Rattfält has shown that the technology works, that the electrodes can for example be put into the strap of a brassiere, in the waistband of underwear or in wristlets, but will it be used?

“There’s a bit left to go; the technical problems are relatively simple and concrete but a new, supplementary infrastructure is needed – someone has to provide the technology and utilise the measurement values that are collected. It’s easier with sport products, where it’s clear who is going to pay for it. But as the population ages, we are going to need to measure more things at home,” Dr Rattfält responds.

Thesis: Smartware electrodes for ECG measurements, design evaluation and signal processing, Linda Rattfält, Department of Biomedical Engineering, Linköping University, 2013.

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