The heart beats, and a pressure wave travels through the arteries, like ripples spreading from a stone thrown into water. The shape of this wave tells us about the stiffness of the vessels: if arteries lose flexibility, the wave changes. But capturing it without a catheter or a bulky blood pressure cuff has been tricky. Now, researchers in Budapest have made a sensor from a flexible conductive thread. The thread is stretched in a zigzag pattern inside an elastic band that presses against the radial artery at the wrist. As the pressure wave passes, the thread deforms, and its electrical resistance changes. That signal is the pulse wave.

First, the sensor was tested on a mechanical pulse simulator — a device that reproduces the pressure wave using a rotating 3D-printed cam. The thread responded to every movement with a repeatability of 0.9999—almost perfect. Then, the sensor was worn on a volunteer's wrist and compared with an optical force sensor, OptoForce. The correlation was 0.988, meaning the wave shapes nearly matched. All key features (the systolic peak, the dicrotic notch, the second rise) appeared at the right times. Only the amplitude of the second peak came out slightly muted: the thread, like taffy, slowly returns to its original state after stretching, which blurs sharp details.

Previously, it was unclear whether such a simple thread could capture the subtle details of the pulse wave that matter for diagnosis. It turns out it can. Now the sensor can be integrated into smartwatch bands to continuously monitor vascular health and catch problems early. Next steps include restoring the true amplitude of the second peak and translating the wave shape into precise blood pressure numbers.