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T-shirt with integrated electronics set to monitor cardiac health

The spiralling cost of healthcare is prompting governments around the world to change the emphasis from treating patients in hospital once something has happened to attempting to prevent those conditions developing.

This approach is seeing the development of a range of devices intended for use by people in their own homes.

Using what are essentially consumer devices, patients can supply information to medical professionals from their homes, rather than attend at surgeries or hospitals. That information can be reviewed and, if necessary, action taken.

One of the attractions of the approach is that, because the devices will be used in the home, they are not subject to the same stringent conditions as the instruments used in medical facilities. That makes them much cheaper and more widely available. Some of the first types of these devices measure blood pressure, blood sugar levels and, in some cases, heart rhythm.

When it comes to heart and circulatory problems, the numbers are staggering. In the UK, more than 80,000 people die each year from coronary heart disease (CHD) and more than 25,000 are younger than 75. Meanwhile, more than 100,000 people a year have heart attacks. In the US, the figures are even starker. Each year, 600,000 people die of heart disease – 25% of all deaths – and almost 1million people will have a heart attack. The costs are equally huge. CHD is said to cost the US more than $100billion a year. In the UK, some £2bn is spent by the NHS on treating and dealing with heart disease.

Steve LaJeunesse, strategic marketing manager for the medical equipment segment with Maxim Integrated, has recently been involved in the development of wearable electronics for health applications. "Why should we do it?," he asked. "A lot of people in the US are older than 60 and live alone. Many have heart issues. If they could wear something 24/7, the data could be captured and events such as heart attacks predicted before they happen – this is all about preventive medicine and wellness."

Maxim cites statistics that claim 80% of heart related deaths can be prevented through information being available and awareness raised. It also believes the 5% of the US population affected by coronary issues consumes $3trillion in annual healthcare costs, while connected home health could be available for as little as $10 a day.

One of Maxim's projects is the FIT telemonitoring shirt, which integrates a three lead ECG, body temperature and motion sensors, as well as processing technology, into a comfortable to wear shirt. LaJeunesse said the idea for the shirt came out of a brainstorming session early in 2012 at the Stanford Design School – ' a very creative environment'. "We built a mock up out of paper to describe how it would work and decided we could do the electronics with what's in the Maxim portfolio."

Partnering with Maxim on the FIT shirt is the National University of Singapore (NUS), which LaJeunesse said has been heavily involved with wearable electronics, and Clearbridge Vital Signs, an NUS spin out. "We started the project in June 2012," LaJeunesse recalled, "and had it working by the end of July."

According to LaJeunesse, he was 'surprised, but then again, not surprised' by the progress. "We've been involved with start ups before and they move more quickly than larger companies like Maxim."
He said the main issues related to mechanical and industrial design. "We had to work out how to get sensors into the shirt and then to get good contact with the body."

The solution to that problem came from Orbital Research, which has developed FDA approved sensors that improve signal pick up by a factor of four.

According to Orbital, ECG electrodes tend to rely on an electrolytic gel to conduct bioelectrical signals from the skin to the electrode, which means you only get good signals when there is a high hydration level at the electrode.

It has developed electrodes which feature surface microstructures that function as the sensing element, removing the need for the electrolytic gel and aggressive skin preparation. These 'features' are embedded in the upper layers of the skin, allowing ion transduction. Signal quality, it claims, is maintained irrespective of the type or duration of activity while the electrodes are being worn.

LaJeunesse said industrial design was important. "The shirt has to be comfortable to wear and has to fit and the mechanical design of the sensors needs to give good skin contact." The top layers of the skin, known as the stratum corneum, comprise dead cells. "We need to penetrate to the layers beneath, where there is a lot of electrical activity," he said. "The little bumps on the electrodes do a good job in getting better signal pick up."

The main aim of the FIT shirt is to provide medical professionals with a three lead ECG. This works by recording the electrical activity that triggers contraction in the heart muscle. The approach is suitable for continuous monitoring of heart rate and its basic rhythm.

Alongside the three lead ECG, which requires four contacts, are sensors which capture temperature and activity related data. All of this information passes through an analogue front end developed by Clearbridge. "It's an ultra low power front end," LaJeunesse asserted, "which produces a digital output and passes that to a microcontroller, where additional filtering is performed, alongside some motion artefact rejection."

The first iteration of the FIT shirt uses a device from Maxim's 16bit MAXQ risc microcontroller portfolio, but the next version of the device – FIT TWO – will be based on an ARM Cortex-M3 core.
"MAXQ mcus have a lot of I/O," LaJeunesse pointed out, "and one of the lowest power consumptions. But, because it's a special core, it hasn't been adopted widely, so we're moving to an ARM based device."

Power is an important element of the design. While the first iterations use batteries, the plan is to take advantage of energy harvesting in the future. "We are working to understand how to use it," LaJeunesse admitted. "Energy harvesting is ahead of its time, but it's getting closer."

One possibility is to use the body's heat, but solar, vibrational and even rf energy are also candidates. "We can use the difference between the body's temperature and the environment to generate power," LaJeunesse said. "With a delta of just 5C, we can generate mWs; enough to power FIT TWO."

But research underway at Wake Forest University in the US is looking at energy harvesting fabrics. In its Power Felt concept, carbon nanotubes encased in plastic fibres are impregnated into the fabric, creating power from the difference between body and ambient temperatures.

However, the biggest problem is physics. "It's the radio," LaJeunesse noted. "We have to put a certain amount of energy into the air for it to be received by a smartphone or a laptop; that's the biggest element."

The advent of more energy efficient Bluetooth protocols has helped the project. "Bluetooth Low Energy (LE) brings the energy consumption down by an order of magnitude," LaJeunesse said. "This allows the FIT shirt to run for 14hours from one charge."

Work is now underway to cut Bluetooth LE consumption further. "Today, it draws a maximum of 50mA and an average of 5mA. In the future, " LaJeunesse said, "it will have a peak of 5mA and an average of 50µA."

Another option is IEEE802.15.6, a standard for short range communication near or inside the body. While potentially supporting data rates of up to 10Mbit/s, this standard needs to take a number of issues into account, including the wearer and the effects of portable antennas. According to LaJeunesse, the Continua Health Alliance in the US – which brings together healthcare providers and technology developers – is backing both approaches.

The technology in the FIT shirt may have wider application. "Clinical and consumer applications are possible," LaJeunesse suggested. "A consumer product wouldn't need the ECG functionality, but would need heart rate, oxygen saturation and activity monitoring, as well as temperature. Clinical applications would need all of those, as well as the ECG function and blood pressure, if we can measure that without a cuff."

But there is one overriding issue for all medical devices – security. "It's important," LaJeunesse asserted, "particularly if there's a diagnosis involved. We've included several layers of encryption: Bluetooth; the underlying data; and the connection. Underlying data is encrypted 'on the fly'," he continued, "using a Maxim patented approach."

While the electronics in the FIT shirt are included in a palm sized snap off module, FIT TWO will feature integrated electronics. "The electronics will be button sized," LaJeunesse predicted. "They will be waterproof so the shirt can be worn and washed." Other sensor technologies are also being explored that LaJeunesse believes will be 'even more wearable' than those currently used.

Eventually, all such devices will take advantage of energy harvesting. "They'll last for life," LaJeunesse said. "Even with today's semiconductor technology, the necessary power consumption levels are within our grasp. We have to be smart, but we are doing it. We now have a small form factor, with invisibility as the goal." he concluded.

Flexible circuit targets cot deaths
German research organisation Fraunhofer is using wearable electronics to address the issue of sudden infant death syndrome; also known as cot death. It believes that, by integrating stretchable pcbs into the romper suits of newborn babies, their breathing can be monitored.

The stretchable pcb, which fits the contours of the body, has been developed by researchers at the Fraunhofer Institute for Reliability and Microintegration IZM in Berlin. The polyurethane based pcb, which stretches to fit the contours of the body, has been fitted with two commercially available sensors and attached to the romper suit, allowing breathing in the chest and stomach areas to be monitored.

"The circuit board we have developed can be manufactured using routine industrial processes," said IZM scientist Manuel Seckel. "Components can be positioned just as precisely as on a standard pcb, thanks to the stability of the stretchable substrate during processing." He claimed textile based electronics may see an offset of up to 5mm over a 0.5m area.

Graham Pitcher

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