Blood pressure can be falsely high if the arm is not positioned correctly

When the arm is in the lap or at the side, a blood pressure reading can be falsely high. But when the arm is supported and at the level of the heart, the blood pressure reading is more likely to be correct.

In a clinical trial, researchers investigated the effect that different arm positions had on blood pressure readings, which are made up of two numbers. The first, systolic, represents the pressure of the blood against the walls of the arteries when the heart beats. The second, diastolic, is the pressure between beats, when the heart is at rest.

For trial participants with their arm in their lap, systolic and diastolic readings skewed about 4 millimeters of mercury higher on average, compared to readings for participants with the arm in the recommended position: at heart level and supported by a desk or table. For participants whose arm hung at their side, the systolic reading was nearly 7 millimeters of mercury higher and the diastolic reading was 4 millimeters of mercury higher, researchers from Johns Hopkins University report online. JAMA Internal Medicine.

About 120 million adults in the United States have high blood pressure — defined as a reading equal to or greater than 130/80 millimeters of mercury — or take blood pressure medication. High blood pressure increases the risk of cardiovascular disease and stroke (.SN: 29.5.18).

To get the most accurate blood pressure reading, medical guidelines recommend that people have their legs uncrossed and feet flat on the floor, with their back supported, their arm positioned correctly, and a suitable blood pressure cuff . But how closely medical offices follow these guidelines with their patients varies, the study authors point out.

This can mean inaccurate readings for some people, which can lead to unwarranted diagnoses of high blood pressure. Using data from a 2017-2018 National Health and Nutrition Examination Survey, Johns Hopkins researchers calculated that, with a cutoff of 130 millimeters of mercury, 54 million adults could be misclassified as having high blood pressure if the arm is not positioned. properly.