Monitoring blood pressure by measuring changes in vessel diameter using ultrasound

Due to the regular stress-strain relationship of biomaterials such as blood vessel walls, the waveform changes of blood vessel diameter and blood pressure can be correlated through the arterial stiffness coefficient. Wearable ultrasound sensors measure the diameter of blood vessels and convert this data into blood pressure.

Figure | Schematic diagram of the working principle of wearable ultrasonic sensors. The ultrasound sensor fixed on the arm with transparent dressing is used for data validation through an arterial catheter on the same arm or a cuff type blood pressure monitor on the opposite arm (source:Nature Biomedical Engineering）

The working principle of wearable ultrasound sensors is shown in the figure above. By emitting ultrasound beams deep into the human body, ultrasound waves are emitted to the target artery, and the anterior and posterior walls of the artery display two peaks in the RF signal.

By tracking arterial wall pulsations through peak motion, arterial diameter waveforms are generated. These waveforms are converted and calibrated into blood pressure waveforms, which are continuous blood pressure measurements that need to be taken.

This measurement method directly focuses on arterial pulsation, does not require invasive measurement, and is not affected by changes in skin characteristics, which can improve the accuracy and stability of blood pressure measurement.

Despite the aforementioned advantages, even the most advanced wearable ultrasound devices currently in use face issues such as isolated acoustic windows leading to measurement errors and a lack of sufficient safety and performance validation.

The wearable ultrasonic sensor developed by the research group combines optimized acoustic and mechanical design, overcoming the limitations of traditional monitoring technology.

Continuous acoustic window and backing layer enhance measurement accuracy

This sensor adopts tightly connected acoustic windows and backing layers, effectively reducing the ringing effect of the transducer and improving the tracking accuracy and measurement stability of arterial wall motion.

It also uses a linear array of 20 ultrasound transducer elements arranged closely, with the spacing between each element reduced to 0.5 millimeters, forming a continuous acoustic window approximately 10 millimeters wide.

This compact structural design brings two significant advantages: comprehensive coverage of the target artery and reduced alignment requirements.

Due to the wider acoustic window, it can fully cover the target arteries, such as the radial and brachial arteries. Even if the sensor moves slightly during wearing, it can still keep the ultrasound beam focused on the target area, reducing signal loss caused by misalignment.

The wide sound window reduces the alignment sensitivity between the artery and the sensor, so in practical use, even if the sensor is not completely aligned with the artery, stable and reliable ultrasound imaging can be provided, reducing measurement deviation caused by position changes.

In addition, a backing layer with a thickness of 500 microns has been added to the sensor design, which plays an important damping role and can reduce the ringing effect of the transducer.

The ringing effect refers to the excess vibration remaining after the transducer is activated, which prolongs the length of the sound pulse and causes signal blurring, thereby affecting the accuracy of the measurement.

The backing layer significantly shortens the duration of the sound pulse by suppressing these excess vibrations, making the reflected signal clearer and sharper.

In addition, the shorter sound pulse length significantly improves the accuracy of arterial wall tracking. Ultrasound signals can therefore more accurately capture the subtle expansion and contraction of arterial walls, providing extremely high spatial resolution.

This improvement is particularly crucial in detecting peripheral arterial pulsations with small changes, ensuring the accuracy and reliability of blood pressure monitoring.

Sensors also have high mechanical flexibility and adhesion, which can firmly adhere to different skin surfaces, suitable for long-term wearing and continuous monitoring, meeting the needs of daily and clinical use.

Through optimized design and a series of experiments on wearable ultrasonic sensors, the research team has conducted detailed characterization of the acoustic characteristics, mechanical flexibility, and durability of the device, ensuring that the sensor can maintain excellent performance in various usage environments.

Multi scenario verification of high reliability in actual medical scenarios

To verify the performance of the sensor, researchers conducted large-scale and rigorous experiments in various clinical environments. Verified by healthy individuals, outpatient patients, intraoperative patients, and postoperative patients in the laboratory, testing scenarios include usage scenarios in daily activities, cardiac catheterization laboratory, and intensive care unit.

The study covers blood pressure monitoring from a static state to dynamic activity, and examines the device's response to posture changes (such as standing, sitting, and lying down) and various physiological stimuli (such as exercise, eating, meditation, etc.). In addition, researchers have conducted a systematic evaluation of stability and reliability in complex medical environments.

The results show that the blood pressure values measured by the sensor in different scenarios are highly consistent with standard clinical equipment, and all results meet international blood pressure monitoring standards, demonstrating the high reliability of the device under actual clinical conditions and supporting its future widespread medical applications.

According to Zhou Sai, wearable ultrasound sensors have a wide range of application prospects, which can be roughly divided into the following categories:

Home and portable health monitoring: It can provide round the clock, continuous blood pressure monitoring for patients with hypertension and those at risk of cardiovascular disease, replacing traditional cuff blood pressure monitors.

Intensive care and postoperative monitoring: In the intensive care unit, this device can serve as a non-invasive alternative to achieve non-invasive and accurate real-time blood pressure monitoring, providing a safer and more comfortable option for critically ill patients who need to monitor blood pressure for a long time, and reducing the risks of infection and thrombosis caused by arterial catheters.

In the field of sports and fitness: For athletes and fitness enthusiasts, this technology can provide real-time blood pressure data to help monitor the body's cardiovascular response during exercise, optimize training plans, and prevent cardiovascular problems caused by intense exercise.

Remote healthcare and health big data analysis: With the popularity of wearable devices and remote healthcare technology, this sensor can be seamlessly integrated into health monitoring systems, helping doctors obtain real-time blood pressure data from patients remotely.

Sleep Medicine and Nighttime Hypertension Monitoring: This wearable sensor can continuously monitor blood pressure during the user's sleep, providing accurate assessment tools for nighttime hypertension and related sleep disorders (such as sleep apnea), thereby optimizing diagnosis and treatment plans.

Chronic disease management and personalized treatment: Through continuous monitoring, equipment can help medical personnel track patients' reactions to medication, adjust treatment plans in real time, and provide more accurate and personalized chronic disease management strategies.

Promote the commercialization of technology

Looking back at the research process, Zhou Sai said that an elderly patient who had suffered from hypertension and cardiovascular disease for many years expressed gratitude to him. This patient said to him:& ldquo; If such devices could have been developed earlier, perhaps many patients could have discovered health hazards earlier without having to worry so much& rdquo;

This statement made Zhou Sai feel that his work is not only scientific research, but also has the potential to bring improvement to people's lives.

Next, the research group plans to continue conducting larger scale clinical trials to validate the performance of the device in different populations, and will cover a wider range of age groups and individuals with different health conditions.

Through these data, the research team hopes to further confirm the universality and performance stability of the device, and accumulate more solid evidence for future regulatory approvals and market promotion.

In addition, they also plan to further develop the device towards miniaturization, making it more lightweight and comfortable, suitable for all-weather wear, and continue to explore the potential applications of ultrasound sensors in other medical fields.

At the same time, the research group plans to use AI technology to improve the accuracy and efficiency of pulse wave analysis, in order to achieve automatic recognition and classification, automatically extract important features from pulse waves, such as rise time, reflection wave position, and peak valley, and enhance the accuracy of analysis.

In addition, personalized health predictions can be made based on each user's historical data, analyzing the trend of pulse wave changes and predicting future cardiovascular health risks.

Through AI technology, it is expected to further develop towards more intelligent remote medical applications. AI can analyze data uploaded from devices to the cloud in real-time and generate health reports or automatic alerts to alert users and doctors of potential health issues. This will help improve the response speed of medical services and enhance medical accessibility in remote areas.

At present, Zhou Sai is pushing wearable ultrasound technology towards commercial scale production and seeking strategic investors and partners.