Wearable Patch to Monitor Blood Pressure Deep Inside Your Body

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

A team of researchers led by the University of California San Diego describe their work in a paper published in Nature Biomedical Engineering. Sheng Xu, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering and the corresponding author of the study, said in a statement:

The new ultrasound patch can continuously monitor central blood pressure in major arteries as deep as four centimeters (more than one inch) below the skin. Physicians involved with the study say the technology would be useful in various inpatient procedures. Dr. Brady Huang, a co-author on the paper and radiologist at UC San Diego Health, said:

A convenient alternative to clinical methods

The device measures central blood pressure — which differs from the blood pressure that’s measured with an inflatable cuff strapped around the upper arm, known as peripheral blood pressure. Central blood pressure is the pressure in the central blood vessels that send blood directly from the heart to other major organs throughout the body.

Medical experts consider central blood pressure more accurate than peripheral blood pressure and also say it’s better at predicting heart disease. Measuring central blood pressure isn’t typically done in routine exams, however. The state-of-the-art clinical method is invasive, involving a catheter inserted into a blood vessel in a patient’s arm, groin, or neck and guiding it to the heart.

A non-invasive method exists, but it can’t consistently produce accurate readings. It involves holding a pen-like probe, called a tonometer, on the skin directly above a major blood vessel. To get a good reading, the tonometer must be held steady, at just the right angle and with the right amount of pressure each time. But this can vary between tests and different technicians.

Co-first author Chonghe Wang, a nanoengineering graduate student at UC San Diego, added:

Tonometers also require the patient to sit still — which makes continuous monitoring difficult — and are not sensitive enough to get good readings through fatty tissue. The UC San Diego-led team has developed a convenient alternative — a soft, stretchy ultrasound patch that can be worn on the skin and provides accurate, precise readings of central blood pressure each time, even while the user is moving. And it can still get a good reading through fatty tissue.

When worn on the neck, the device records central blood pressure in the carotid artery (CA), internal jugular vein (Int JV) and external jugular vein (Ext JV)

When worn on the neck, the device records central blood pressure in the carotid artery (CA), internal jugular vein (Int JV), and external jugular vein (Ext JV). (Image: courtesy of Chonghe Wang / Nature Biomedical Engineering)

The patch was tested on a male subject, who wore it on the forearm, wrist, neck, and foot. Tests were performed both while the subject was stationary and during exercise. Recordings collected with the patch were more consistent and precise than recordings from a commercial tonometer. The patch recordings were also comparable to those collected with a traditional ultrasound probe.

Making ultrasound wearable

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). Wang said:

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.

he island-bridge structure allows the patch to be flexible and stretchable.

The island-bridge structure allows the patch to be flexible and stretchable. (Image: courtesy of Chonghe Wang / Nature Biomedical Engineering)

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.

Next steps

Researchers note that the patch still has a long way to go before it reaches the clinic. Improvements include integrating a power source, data processing units, and wireless communication capability into the patch, Xu said:

The team is looking to collaborate with experts in data processing and wireless technologies for the next phase of the project.

Provided by: University of California — San Diego [Note: Materials may be edited for content and length.]

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