How Arm Position Affects Blood Pressure Accuracy
Accurate blood pressure readings are crucial for diagnosing hypertension, a major risk factor for heart disease. Recent studies show that incorrect arm positioning can lead to inaccurate readings, potentially affecting millions of people. Learn how to position the arm correctly to ensure reliable blood pressure measurements.
Medical News
Study Findings on Arm Position and Blood Pressure Overestimation
In a study published in October 2024, investigators measured the effects of arm position on blood pressure (BP) measurements. Guidelines for blood pressure measurement recommend that the arm be supported on a desk or table and the middle of the blood pressure cuff be at heart level. However, other positions such as the arm being unsupported at the side or resting on the lap are frequently used in measurements.
133 subjects, aged 18 to 80, had their blood pressure measured all three ways. The researchers reported that supporting the arm on the lap overestimated systolic BP by a mean of 3.9 mmHg (1 mmHg is the pressure generated by a 1-millimeter-high column of mercury) and diastolic BP by mean of 4.0 mmHg. An arm unsupported at the subject’s side overestimated systolic BP by a mean of 6.5 mm Hg and diastolic BP by a mean of 4.4 mmHg.
Why Arm Position Affects Blood Pressure Accuracy
There may be several reasons why arm position may affect blood pressure. The distance between the heart and the cuff increases when the arm is positioned in the lap or at the side compared to being supported on a desk. When the arm is positioned below the heart this may lead to an increase in hydrostatic pressure (force exerted by gravitational pull) in the arm’s brachial artery. There may also be decreased venous return of blood with the arm down compared to a supported arm and compensatory vasoconstriction ( the narrowing or constriction of blood vessels by small muscles in their walls) may lead to an increase in vascular resistance and an increase in BP. Finally, an unsupported arm may cause some muscular contraction, which might cause transient increases in BP.
The authors suggested that non-adherence to correct blood pressure measuring guidelines could result in up to 16% of US adults, equating to 40 million individuals, being misclassified as hypertensive when using a systolic blood pressure cutoff of 140 mm Hg and higher.
Beyond Arm Position: Other Factors Affecting Blood Pressure Readings
In this study, the method by which blood pressure was measured caused significant overestimations in both systolic and diastolic pressure. In another study, by some of the same authors, it was reported that using a regular-sized blood pressure cuff on a small-armed individual underestimated systolic blood pressure by 3.6 mmHg. Use of a regular-sized blood pressure cuff overestimated systolic blood pressure by 4.8 mmHg on subjects who required a large-sized blood pressure cuff, and use of a regular-sized cuff on someone who required an extra-large-sized blood pressure cuff overestimated systolic blood pressure by 19.5 mmHg. There are a number of other factors that can affect blood pressure results, such as crossing the legs while taking measurement, talking during measurement, or the so-called white-coat effect of blood pressure elevation just being in the presence of a health care professional.
Hypertension is a significant risk factor for stroke and heart disease, and treating it with medication can reduce that risk. Other studies have found even greater differences in blood pressure readings depending on arm position. Measuring blood pressure correctly with the correct positioning and the right-sized cuff should increase diagnostic accuracy and allow more precise patient selection for treatment. Repetition of borderline blood pressure elevations or having patients take their blood pressure at home may also improve accuracy.
References
Liu H, Zhao D, Sabit A, et al. Arm Position and Blood Pressure Readings: The ARMS Crossover Randomized Clinical Trial. JAMA Intern Med. Published online October 07, 2024. Retrieved from: https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2824754?guestAccessKey=f167dda3-8cad-4f34-99ca-79865446c64f
Ishigami J, Charleston J, Miller ER, Matsushita K, Appel LJ, Brady TM. Effects of Cuff Size on the Accuracy of Blood Pressure Readings: The Cuff(SZ) Randomized Crossover Trial. JAMA Intern Med. 2023;183(10):1061–1068. Retrieved from: https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2807853
Kallioinen N et al. Sources of inaccuracy in the measurement of adult patients' resting blood pressure in clinical settings: a systematic review. J Hypertens. 2017;35(3):421-441. Retrieved from: https://pmc.ncbi.nlm.nih.gov/articles/PMC5278896/#T2
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