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The blood pressure readings on the wrist and arm are often very different

HOBART, Tasmania: Researchers report that the blood pressure measured at the wrist is generally higher than the pressure measured at the upper arm, which affects the accuracy of the devices that measure the blood pressure.

Current hypertension recommendations are based on blood pressure measured with a brachial cuff, of the type commonly used in doctor's offices, and applied to the arm.

But many devices used by patients at home, including increasingly available hand-held monitors, measure blood pressure at the wrist and in other places.

Dr. James E Sharman, of the University of Tasmania, Hobart, Australia, and his team measured blood pressure following the arm and wrist of 180 older and middle aged individuals who had undergone coronary angiography.

The systolic blood pressure – the highest figure in a blood pressure reading reflecting pressure in the arteries when the heart beats – increased an average of 5.5 mmHg on the wrist compared to the upper arm, reported researchers in hypertension.

"We expected to see a lot of variation in how systolic blood pressure changed from upper arm to wrist, but we were interested in seeing the number of people (14%) with what can be considered very big differences, on average 20 mmHg (or more), "said Sharman in an email.

"Thus, the magnitude of variation between individuals was considerable."

Less than half of the patients had a systolic pressure reading of the wrist less than 5 mmHg from the arm; for 46%, the readings differed by 5 mmHg or more, including 27% with readings differing by 10 mmHg or more.

One in nine participants (11%) had a lower systolic pressure reading of 5 mmHg or more than their upper arm.

On average, the systolic blood pressure of the wrist was 12.9 mmHg higher than the systolic pressure measured in the aorta, the main artery circulating the blood from the heart to the rest of the body.

The researchers found that more than half of this difference was due to the difference in pressure between measurements of the aorta and upper arm and the rest, unlike the measurements of the upper arm and wrist .

"If you search online, you will find that there are hundreds of devices available for sale, many of which measure blood pressure with an armband or wrist band," Sharman said.

"Our research adds even more weight to the evidence that the vast majority of these wrist devices will not record blood pressure values ​​comparable to the clinical standard of cuff blood pressure."

Sharman suggested to doctors and patients to use a "simple to use" and comprehensive guide to measuring home blood pressure, published in 2016 by the Australian Family Physician journal.

"The guide provides instructions on the standardized method, as well as a journal for recording blood pressure values."

He added, "The results of the study feed a larger story on the need to improve the accuracy of blood pressure monitors in general."

The recommendations for blood pressure are based on the external measurements of the armband, said Dr. Giacomo Pucci of the University of Perugia and University Hospital of Terni in Italy, who did not participate in the study.

"Unfortunately," Pucci told Reuters Health, the pressure readings taken on the outside are distorted with respect to the blood pressure measured inside an artery. And, "we are not able, at this time, to predict the degree of this distortion in each individual in a non-invasive manner, so we must continue to rely on noninvasive brachial BP" as substitute for internal measures.

"The availability on the market of devices offering non-invasive assessment of central blood pressure is becoming increasingly important," he said. "Unfortunately, many of these devices lack scientific knowledge, more research is needed in this area, and a rigorous assessment of the quality of the new devices is obviously required."

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