A Blood Pressure Monitor to Wear on Your Wrist

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THURSDAY, April 16 (HealthDay News -- Imagine being able to check your blood pressure with a quick glance at your wrist.

Engineers at the Massachusetts Institute of Technology (MIT) have produced a prototype of such a device, which they hope will overcome the limitations of current blood pressure-monitoring systems.

"A wearable blood pressure monitor can get data regularly," said H. Harry Asada, an MIT mechanical engineer who has led the development of the device. "If you are taking medication to lower your blood pressure, it can tell you if you are taking too much or too little."

Most people now have their blood pressure checked only when they visit a doctor. However, there are worries that office readings might not be accurate because of "white coat hypertension," higher-than-normal blood pressure caused by the nervousness of being in a doctor's office.

Blood pressure measurements at home usually require putting on an inflatable cuff, a procedure that many people find annoying. By contrast, the prototype device developed at MIT is a device about the size of a cell phone, worn on the wrist and hooked up to a sensor that is a simple finger ring.

"It's a combination of wristwatch and ring, a little larger than a standard wristwatch," said Asada, director of MIT's d'Arbeloff Laboratory for Information Systems and Technology.

It might seem simple, but its development required solving a tricky engineering problem in three dimensions because blood pressure goes up or down as a hand is raised or lowered.

"As people raise or lower their arms, different hydrostatic pressures apply to the sensor," Asada said. "We have to correlate the sensor reading to changes in hydrostatic pressure."

That correlation must be done in three dimensions because an arm can move in any direction. "If we know the orientation of the hand, we can assume the arm length of the wearer, depending on age and height," he said. "We can do some quick trigonometric calculations to find the height of the hand relative to the shoulder. Then we can calibrate the sensor reading."

The MIT engineers have been working with commercial sponsors to develop a marketable version of the wearable sensor. "We should be ready to commercialize it in four to five years at most," Asada said. The cost should be comparable to that of existing electronic devices, he added.

Along with providing immediate readings of blood pressure, the sensor could allow continuous monitoring, Asada said. "The data could be transmitted to the Internet," he said. "But because of security considerations, there are non-trivial issues to be resolved. We are still debating how to get continuous readings, and at what cost."

The continuous readings of blood pressure promised by the new device would be "extremely helpful" for the many people who have great variations in blood pressure throughout the day, said Dr. Adolph Hutter Jr., a professor of medicine at Harvard Medical School and a clinical cardiologist at Massachusetts General Hospital.

"If the technology works, then I think it would be a significant addition," Hutter said. "But it has to be comfortable for the patient, and it has to be proved in clinical trials. It has to be shown to be a reliable indicator of blood pressure as shown by standard methods."

SOURCES: H. Harry Asada, Ph.D., professor, engineering, and director, Massachusetts Institute of Technology d'Arbeloff Laboratory for Information Systems and Technology, Boston; Adolph Hutter Jr., M.D., professor, medicine, Harvard Medical School, and clinical cardiologist, Massachusetts General Hospital, Boston

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