Portable ultrasound patch monitors blood pressure

A new portable ultrasound patch, which non-invasively monitors blood pressure in deep arteries under the skin, could help people detect cardiovascular problems earlier and with greater accuracy.

In the tests, the patch was made as well as some clinical methods for measuring blood pressure.

Applications include real-time monitoring of changes in blood pressure in patients with heart or lung disease, as well as critically ill or undergoing surgery. The patch uses ultrasound, so it could be used to follow noninvasively other vital signs and physiological signals from locations inside the body.

A team of researchers led by the University of California at San Diego describes their work in an article published on September 11 Nature Biomedical Engineering.

"Until now, wearable devices were limited to detecting signals on the surface of the skin or just below it.But it's like seeing the tip of the iceberg," said Sheng Xu. , professor of nanoengineering at UC San Diego Jacobs School. of Engineering and the corresponding author of the study, said. "By integrating ultrasound technology into wearable devices, we can begin capturing a large number of other non-invasive signals, biological events, and activities that go below the surface. We add a third dimension to the detection range of portable electronic devices. . "

The new ultrasound patch can continuously monitor central blood pressure in the main arteries to a depth of up to four centimeters (more than one inch) under the skin.

Doctors involved in the study claim that the technology would be useful in various hospital procedures.

"This could be a great addition to cardiovascular medicine," said Brady Huang, co-author of the journal and radiologist at UC San Diego Health. "In the operating room, especially in complex cardiopulmonary procedures, accurate real-time assessment of central blood pressure is needed – it is there that this device has the potential to supplant traditional methods. "

A practical alternative to clinical methods

The device measures central blood pressure that differs from the measured blood pressure with an inflatable cuff attached around the arm, called 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 believe that central blood pressure is more accurate than peripheral blood pressure and also say that it is better to predict heart disease.

However, the measurement of central blood pressure is not usually done during routine examinations. The advanced clinical method is invasive and involves a catheter inserted into a blood vessel in the arm, groin or neck of a patient and guiding it to the heart.

A non-invasive method exists, but it does not produce accurate readings. It involves placing a pen-shaped probe, called tonometer, on the skin directly over a large blood vessel.

To get a good reading, the tonometer needs to be kept steady, just at the right angle and with the right amount of pressure each time. But this can vary between tests and different technicians.

"It depends a lot on the operator, even with the proper technique, if you move the tip of the tonometer only one millimeter, the data is distorted, and if you push the tonometer too hard, it will put too much pressure on the ship, which also affects the data, "said Chonghe Wang, co-first author and graduate student in nanoengineering at UC San Diego.

Tonometers also require the patient to remain seated, which makes monitoring difficult and not sensitive enough to get good readings through fat tissue.

The team led by UC San Diego has come up with a practical alternative: a flexible and extensible ultrasound patch that can be worn on the skin and provides accurate and precise readings of central blood pressure at each times, even when the user is moving. He can always have a good reading through the adipose tissue.

The patch was tested on a male subject, which focused on the forearm, wrist, neck and foot. The tests were performed while the subject was still and during exercise.

The recordings collected with the patch were more consistent and accurate than the recordings of a commercial tonometer. Patch recordings were also comparable to those collected with a traditional ultrasound probe.

Make ultrasound portable

"A major breakthrough in this work is to turn ultrasound technology into a portable platform, which is important because we can now begin to monitor the major blood vessels deep under the skin in a continuous and non-invasive way, not only in shallow tissues ". I said.

The patch is a thin sheet of silicone elastomer with a structure called "island-bridge" – a series of small electronic components (islands) each connected by spring-shaped cables (bridges). Each island contains electrodes and devices called piezoelectric transducers that produce ultrasonic waves when electricity passes through them. The bridges that connect them are made of fine copper wire and resembling springs. The island structure allows the entire room to adapt to the skin and stretch, bend and twist without compromising the electronic function.

The patch uses ultrasonic waves to continuously record the diameter of a pulsed blood vessel located four centimeters deep from the skin. This information is then translated into a waveform with the help of custom software.

Each peak, valley and notch of the waveform, as well as the general shape of the waveform, represent a specific activity or event in the heart. These signals provide many detailed information to doctors assessing the cardiovascular health of a patient. They can be used to predict heart failure, determine if the blood supply is correct, and so on.

Next steps

The researchers note that the patch still has a long way to go before reaching the clinic. Improvements include the integration of a power source, data processing units and a wireless communication capability in the patch.

"At the moment, these capabilities need to be provided by cables from external devices, so if we want to go from bench to bedside, we have to integrate all these components," Xu said.

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