Wearable Flexible Doppler Ultrasound May Allow for Long-Term Blood Flow Monitoring After Ischemic Events

  • March 18, 2022

The device may help prevent thrombosis and restenosis complications after surgery, particularly in patients with fragile skin.  Although thrombosis can occur within 72 hours, and patients are supposed to be checked every hour for capillary fill and skin color, these assessments might only happen sporadically in the hospital and not at all after discharge, wrote the study’s lead author Xue Feng, PhD, an Associate Professor in the Department of Electronic Engineering at Tsinghua University in Beijing, China, and colleagues.  “The device could be used for blood flow velocity monitoring after vascular reconstruction procedures or preventive home care exams of some chronic vessel diseases, such as diabetic foot,” the study authors wrote.  The wearable device addresses long-term monitoring issues and is non-invasive, the authors added.  “Compared to the clinical ultrasound machine, the device avoids complex imaging (for Doppler angle measuring), requires no experienced operator, applies much smaller pressure, and thus helps with long-term monitoring,” wrote the researchers.

Typically, the most common way to measure blood flow is to use a handheld ultrasound device, which is rigid and can need to be pressed against the skin.  Doppler probes can also be implanted for continuous monitoring; however, are limited by wired connection requirements.

This new flexible device is 1 mm thick, weighs .75 grams, and conforms to the skin, the study authors wrote.  It can also note rapid changes in real time, including the absolute mean and peak velocity of blood flow.  The device was first tested on an ultrasound phantom and then on human arteries.  To test the flexible device, investigators measured the pulse and frequency (stable at approximate 5 MHz) response of the transducer before and after it was bent 500 times.  They found that the performance remained unchanged.

Researchers also measured the device’s accuracy by monitoring the behavior of the brachial artery from the fully closed state to an open state using an inflatable cuff to close and open the blood flow.  They found that the signal as the artery opened was more obvious than the signal of the blood flow; however, could be addressed by increasing the transmit frequency or reducing the inclination angle.

The study also compared the pressure the device puts on the skin with that of a traditional probe and found that the flexible device applied minimal pressure compared with the traditional rigid device.  The additional pressure from the larger ultrasound might result in problems with long-term monitoring, particularly for postoperative patients with fragile skin, the study said.

One challenge with the device is that it requires people to keep still while taking readings.  In addition, future work will improve wireless communication and the power supply to improve the overall wearability and reduce power consumption.

The study was funded by the National Natural Science Foundation of China.

REFERENCE:  Neurology Today; 05 NOV 2021; Dawn Fallik

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