Ellen Phiddian
Cosmos science journalist
Arm position has an effect on blood pressure readings, according to a new study.
The study, published in JAMA Internal Medicine, finds that putting your hand in your lap or leaving it dangling down your side results in a higher blood pressure reading than if you’d rested it on a desk.
This means that hypertension may be overestimated and misdiagnosed, according to the US team of researchers.
Blood pressure is supposed to be measured when a patient is sitting down, with their feet flat on the floor, and their arm resting on a table or desk.
This ensures that the sphygmomanometer – the inflatable arm cuff and attached gauge – gets the most accurate reading.
But, the researchers point out, clinicians often take blood pressure readings when the patient is in a different position – particularly when there isn’t a table convenient.
The researchers recruited 133 volunteers, aged between 18 and 80, for this study.
Participants each had their blood pressure measured in 3 different ways, in a randomised order: with their hand on a desk, down their side, or in their lap.
Lap and side positions consistently gave participants higher blood pressure readings than desk positions.
This was true for both the systolic (top) and diastolic (bottom) numbers on blood pressure readings.
Readings were 3.9-6.5mm Hg higher, on average. Leaving the arm at the side prompted particularly high readings.
These patterns were “generally consistent” across age, gender, and other demographic groups, according to the paper. People with hypertension had “more extreme” differences.
These differences are large enough to prompt a misdiagnosis of hypertension in a large proportion of people, according to the researchers.
“Blood pressure readings in either position were sufficiently high to raise concerns for overdiagnosis and over-treatment,” write the researchers in their paper.
The researchers propose several reasons for why arm positions have an effect on readings: the height of the cuff relative to the heart, muscle contraction in unsupported arms, and the amount of work veins and arteries do when the arm is in a different position.
The team says that people should be aware of this discrepancy so they can take blood pressure readings more accurately, both in clinical contexts and in home reading.
“Education and training of both clinical staff and patients regarding BP measurement is essential for hypertension control and cardiovascular disease prevention,” write the researchers in their paper.
