Device uses sound waves to gather blood pressure data from blood vessels, monitoring the response with ultrasound.
Solving a decades-old problem, a multidisciplinary team of Caltech researchers has figured out a method to noninvasively and continually measure blood pressure anywhere on the body with next to no disruption to the patient. A device based on the new technique holds the promise to enable better vital-sign monitoring at home, in hospitals, and possibly even in remote locations where resources are limited.
The new patented technique, called resonance sonomanometry, uses sound waves to gently stimulate resonance in an artery and then uses ultrasound imaging to measure the artery's resonance frequency, arriving at a true measurement of blood pressure. In a small clinical study, the device, which gives patients a gentle buzzing sensation on the skin, produced results akin to those obtained using the standard-of-care blood pressure cuff.
"We ended up with a device that is able to measure the absolute blood pressure -- not only the systolic and diastolic numbers that we are used to getting from blood pressure cuffs -- but the full waveform," says Yaser Abu-Mostafa (PhD '83), professor of electrical engineering and computer science and one of the authors of a new paper describing the technique and device in the journal PNAS Nexus. "With this device you can measure blood pressure continuously and in different sites on the body, giving you much more information about the blood pressure of a person."
"This team has been working for almost a decade, trying to build something that makes a difference, that is good enough to solve a real clinical problem," says Aditya Rajagopal (BS '08, PhD '14), visiting associate in electrical engineering at Caltech, research adjunct assistant professor of biomedical engineering at USC, and a co-author of the new paper. "Many groups, including tech giants like Apple and Google, have been working toward a solution like this, because it enables a spectrum of patient-monitoring possibilities from the hospital to the home. Our method broadens access to hospital-grade monitoring of blood pressure and cardiac health metrics."
Blood pressure 101
Blood pressure is simply the force of blood pushing on the walls of the body's blood vessels as it gets pumped around the body. High blood pressure, or hypertension, is related to risk of heart attack, stroke, chronic kidney disease, and other health problems. Low blood pressure, or hypotension, can also be a serious problem because it means the blood is not carrying enough oxygen to the organs. Taking regular measurements of blood pressure is considered one of the best ways to monitor overall health and to identify potential problems.
Most of us have experienced the cuff-style measurement of blood pressure. A nurse, doctor, or machine inflates a cuff that fits around the upper arm until blood can no longer flow, and then slowly releases the air from the cuff while listening for the sound that blood makes as it once again begins to flow. The pressure in the cuff at that point corresponds to the blood pressure in the patient's arteries. But this technique has limitations: It can only be performed periodically, as it involves occluding a blood vessel, and can only collect data from the arm.
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