Commonly used arm positions can significantly overestimate blood pressure values, study finds

A study by Johns Hopkins Medicine researchers concludes that commonly used methods of positioning the patient’s arm during blood pressure (BP) testing can significantly overestimate test results and lead to misdiagnosis of hypertension.

In a report on the study, published October 7 in JAMA Internal MedicineThe investigators examined the effects of three different arm positions: one arm supported on a desk, one arm supported on knees, and an unsupported arm hanging at the patient’s side.

Researchers found that abdominal support overestimated systolic pressure (the highest number in a blood pressure measurement) by almost 4 mmHg, and that an unsupported arm hanging at the side overestimated systolic pressure by almost 7 mmHg.

The results confirm that arm position makes a “huge difference” when it comes to accurate blood pressure measurement, says Tammy Brady, MD, Ph.D., vice chair of clinical research at the department. of Pediatrics from Johns Hopkins University School of Medicine. Medicine, medical director of the Pediatric Hypertension Program at Johns Hopkins Children’s Center, deputy director of the Welch Center for Prevention, Epidemiology, and Clinical Research and senior author of the study.

And they emphasize the importance of following clinical guidelines calling for firm support on a desk or other surface when measuring blood pressure, the investigators add.

According to the American Heart Association, nearly half of American adults have high blood pressure, a diagnosis made when the measured force of blood flowing through blood vessels is greater than what is generally considered normal, averaging 120/80 .

Untreated high blood pressure increases the risk of stroke, heart attack and other serious cardiovascular diseases. Because hypertension can cause minimal to no symptoms, early and frequent detection during routine checkups is considered the cornerstone of hypertension management.

In most cases, lifestyle changes such as weight loss, healthy eating and exercise, and treatment with various medications can keep blood pressure under control.

The latest clinical practice guidelines from the American Heart Association emphasize several key steps for accurate measurement, including proper cuff size, back support, feet flat on the floor with legs uncrossed and an appropriate arm position, in which the middle of an adjustable blood pressure cuff is positioned mid-heart on an arm resting on a desk or table.

Despite these recommendations, researchers say blood pressure is too often measured with patients seated on an examination table without, or inadequate, arm support. In some cases, a clinician holds the arm or the patient holds an arm in their lap.

In the new Johns Hopkins study, researchers recruited 133 adult participants (78% Black, 52% female) between August 9, 2022 and June 1, 2023. The study participants, aged 18 to 80 , were sorted randomly. into one of six possible groups that differed according to the order of the three sitting arm positions.

Measurements were taken during a single visit between 9 a.m. and 6 p.m. Before blood pressure measurements were taken, all participants first emptied their bladders and then walked for two minutes to mimic a typical clinical scenario in which people enter a clinic or office before screening. . They then underwent a five-minute seated rest period with their backs and feet supported.

Each person, wearing a blood pressure cuff selected and sized according to their arm size, underwent three sets of triplicate measurements with a digital blood pressure monitor, 30 seconds apart.

At the end of each set of three measurements, the cuff was removed, participants walked for two minutes and rested for five minutes. On the same visit, they then underwent a fourth series of triplicate measurements with their arm resting on a desk, a series used to account for well-known variations in blood pressure readings. All measurements were conducted in a quiet, private space, and participants were asked not to talk to the researchers or use their phones during the screening.

Researchers found that blood pressure measurements obtained with arm positions frequently used in clinical practice (one arm on the lap or not supported at the side) were significantly higher than those obtained when the arm was supported on a desk , the recommended standard arm position.

Supporting the arm on the knees overestimated systolic blood pressure (the highest number in a reading, or the force of blood flow as it is pumped out of the heart, by 3.9 mmHg) and diastolic blood pressure ( the lower number, or the pressure in the arteries when the heart is pumped out of the heart). the heart rests between beats, by 4.0 mmHg. An unsupported arm at the side overestimated the systolic by 6.5 mmHg and the diastolic by 4.4 mmHg.

“If you routinely measure blood pressure with an unsupported arm and that gives you an overestimated BP of 6.5 mmHg, that represents a potential difference between a systolic BP of 123 and 130, or 133 and 140, which is considered stage 2 hypertension,” says Sherry Liu, MHS, epidemiology research coordinator at the Welch Center for Prevention, Epidemiology, and Clinical Research, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health and author of the study.

The investigators caution that their study results may only apply during screenings with automated blood pressure devices and may not apply to readings taken with other blood pressure devices.

However, Brady says, the findings suggest that clinicians need to pay more attention to best practice guidelines and that patients “need to advocate for themselves in clinical settings and when measuring their blood pressure at home.”