Monitoring of heart performance during daily life or exercise may be possible in due course with a postage stamp-sized ultrasound device affixed to the body. Researchers from the University of California San Diego, United States, demonstrated a first version of their flexible, wearable heart monitor Nature.
Echocardiography is a common technique to visualize the performance of the heart and the blood flows in and around the heart. With existing equipment for echocardiography, this can almost only be done in specialist environments such as the hospital, while abnormal heart activity is often visible at unexpected times or during exercise. The portable devices that are now used for long-term monitoring in daily life only record the heart rate, the information from which is much more limited.
The prototype is stuck to the body like a plaster. It is 1.9 by 2.2 centimeters and 0.9 millimeters thick. When the body moves, the sticker moves with it: it can both bend and stretch. It consists of several layers, including liquid metal electrodes and flexible and stretchable piezoelectric conductors (where pressure produces electrical voltage) that activate echo sensors. The echo sensors are arranged in a cross to visualize the heart in different dimensions.
The patch has been tested at rest and in action. The latter on a test subject on an exercise bike. Compared to traditional ultrasound equipment, the prototype produces images of comparable quality, the researchers report. Although until now only the volume of one of the heart chambers has been looked at, not the entire heart and the blood flows around it.
“The fact that they manage to generate this image with flexible and stretchable materials is very clever,” says Massimo Mischi, professor of Signal Processing Systems at Eindhoven University of Technology. “Echo images are reconstructed from the echo signals by determining the relative position to the echo equipment. With flexible and stretchable materials, the position keeps changing, and they still managed to generate a good image.”
Not wireless yet
“It is really a first prototype, there is still a lot missing,” says Mischi. “The sticker is not yet wireless, but that must of course be done in order to be able to use it in everyday life and during exercise. And they have now only measured the volume of the heart chamber, which is a relatively simple application.”
The group that publishes this research is at the forefront of this technology worldwide, Mischi knows. “We are also working on ultrasound stickers in the Netherlands, albeit via a different approach. I don’t know what technology it will ultimately be, for example it must also be cheap to produce, but I strongly believe in the development towards highly mobile ultrasound.”
“It can pay off a lot,” says Mashi. “Images can be taken outside the hospital, largely by patients themselves or by a GP. You free up space in the hospital and a specialist who now has to make recordings manually. That specialist can then focus on assessing the images. In addition to cardiology, it can also be very useful for pregnancy monitoring, for example. And if it becomes as cheap as we envision, it will also significantly improve healthcare in poorer countries.”
A version of this article also appeared in the newspaper of February 7, 2023