Wearable ultrasound patch tracks blood pressure in a deep artery or vein. (Credit: Chonghe Wang/Nature Biomedical Engineering)

A new wearable ultrasound patch that non-invasively monitors blood pressure in arteries deep beneath the skin could help people detect cardiovascular problems earlier on and with greater precision. In tests, the patch performed as well as some clinical methods to measure blood pressure.

Applications include real-time, continuous monitoring of blood pressure changes in patients with heart or lung disease, as well as patients who are critically ill or undergoing surgery. The patch uses ultrasound, so it could potentially be used to non-invasively track other vital signs and physiological signals from places deep inside the body.

The new patch can continuously monitor central blood pressure in major arteries as deep as four centimeters (more than one inch) below the skin. The patch is a thin sheet of silicone elastomer patterned with what’s called an island-bridge structure — an array of small electronic parts (islands) that are each connected by spring-shaped wires (bridges). Each island contains electrodes and devices called piezoelectric transducers, which produce ultrasound waves when electricity passes through them. The bridges connecting them are made of thin, spring-like copper wires. The island-bridge structure allows the entire patch to conform to the skin and stretch, bend and twist without compromising electronic function.

The patch uses ultrasound waves to continuously record the diameter of a pulsing blood vessel located as deep as four centimeters below the skin. This information then gets translated into a waveform using customized software. Each peak, valley and notch in the waveform, as well as the overall shape of the waveform, represents a specific activity or event in the heart. These signals provide a lot of detailed information to doctors assessing a patient’s cardiovascular health. They can be used to predict heart failure, determine if blood supply is fine, etc.