Tammy Brady and colleagues at Johns Hopkins University conducted clinical trials and found that incorrect arm position when measuring blood pressure can overestimate readings by more than six millimeters of mercury. The ARMS crossover randomized trials involved 133 volunteers (53 percent women) from Baltimore aged 18–80 (mean 57) years. Thirty-six percent of the participants had blood pressure of 130 mmHg or more, and 41 percent had a body mass index of 30 kilograms per meter squared or more. They were all randomly assigned to have their blood pressure measured with their arm lying on a table with the cuff at heart level (as recommended by clinical guidelines), lying on their lap, or hanging freely without support. To account for natural variability in blood pressure, everyone then had the measurement repeated with their arm on the table. A report on the work was published in the journal JAMA Internal Medicine.
It turned out that when measuring on the arm lying on the knees, the results of systolic pressure measurements are overestimated on average by 3.9, and diastolic by 4.0 mm Hg. When measuring on the arm without support, these indicators were 6.5 and 4.4 mm Hg, respectively. When stratifying the results by the presence of arterial hypertension, age, obesity, and seeking medical care during the previous year, the identified patterns persisted in all subgroups. Thus, incorrect arm positions when measuring pressure, often encountered in practice, can lead to incorrect diagnosis and overestimation of the degree of arterial hypertension.