First noninvasive method to continually measure true blood pressure
Solving a decades-old problem, a multidisciplinary team of 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 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 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 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.
Physicians would very much like to have continuous readings that provide full waveforms of a patient's blood pressure, and not only peripheral measurements from an arm but also central measurements from the chest and other parts of the body. To get the full information they need, intensive care physicians and surgeons sometimes resort to inserting a catheter directly into the artery of critical patients (a practice known as placing an arterial line, or "a-line"). This is invasive and can be risky, but, until now, it has been the only way to get a continuous readout of true blood pressure. In some cases, such as problems with heart valves, full blood-pressure waveforms can provide physicians with diagnostic information that they cannot get any other way.
"There's a lot of information in that waveform that is really valuable," says a co-author of the paper. And other blood pressure devices developed over the last decade or two require a calibration step that emergency physicians simply do not have time for, the author says. "I need to be able to put something on a patient and have it work immediately."
The new device fits the bill. The current prototype, built and tested by a spin-off company called Esperto Medical, is housed in a transducer case smaller than a deck of cards and is mounted on an armband, though the researchers say it could eventually fit within a package the size of a watch or adhesive patch. The team aims for the device to first be used in hospitals, where it would connect via wire to existing hospital monitors. It could mean that doctors would no longer have to weigh the risks of placing an a-line in order to get the continuous monitoring of real blood pressure for any patient.
Eventually, the author says their device could replace blood pressure cuffs as well. "Blood pressure cuffs only take one measurement as often as you run the cuff, so if you're asking patients to monitor their blood pressure at home, they have to know how to use the device, they have to put it on, and they have to be motivated to record the information, and I would say a majority of patients do not do that,” says the author. "Having a device like ours, where it is just place and forget, you can wear it all day, and it can take however many measurements your provider wants, that would allow for better, precision dosing of medication."
https://academic.oup.com/pnasnexus/article/3/7/pgae252/7717708
