blood pressure

For real, we may be taking blood pressure readings all wrong

For people who had high blood pressure readings only when sitting (normal readings while lying down), there was no statistically significant difference in risk of coronary heart disease, heart failure, or stroke compared to people with normal blood pressure. The only statistically significant differences were a 41 percent higher risk of fatal coronary heart disease (compared to the 78 percent seen in those with high readings lying down) and an 11 percent higher risk of all-cause mortality.

(In this study, high blood pressure readings were defined for both positions as those with systolic readings (the top number) of 130 mm Hg or greater or diastolic readings (the bottom number) of 80 mm Hg or greater.)

The people with the highest risks across the board were those who had high blood pressure readings while both sitting and lying down.

“These findings suggest that measuring supine [lying down] BP may be useful for identifying elevated BP and latent CVD risk,” the researchers conclude.

Strengths and hypotheses

For now, the findings should be considered preliminary. Such an analysis and finding should be repeated with a different group of people to confirm the link. And as to the bigger question of whether using medication to lower supine blood pressure (rather than seated blood pressure) is more effective at reducing risk, it’s likely that clinical trials will be necessary.

Still, the analysis had some notable strengths that make the findings attention-worthy. The study’s size and design are robust. Researchers tapped into data from the Atherosclerosis Risk in Communities (ARIC) study, a study established in 1987 with middle-aged people living in one of four US communities (Forsyth County, North Carolina; Jackson, Mississippi; suburban Minneapolis, Minnesota; and Washington County, Maryland).

Your doctor’s office could be reading your blood pressure all wrong

blood pressure, health, hypertension, JAMA, Science / DJ Henderson / October 8, 2024

Under pressure

Before participants took readings in any of the positions, the researchers had them simulate walking into a doctor’s appointment. They walked for two minutes and then sat calmly in position for five minutes before taking the three readings. Before moving onto the next position, they got up and walked again and sat for another five minutes. The participants were also randomized into groups that took the first three readings (desk 1, lap, side) in different orders, with all groups ending on desk 2.

The researchers then compared the differences between desk 1 and desk 2 to differences between lap and desk 1 and side and desk 1 for each participant. The desk 1-desk 2 differences captured intrinsic variability of blood pressure reading within each participant. The comparisons to lap-desk 1 and side-desk 1 captured changes based on the improper arm positions.

In all, there was little difference in the desk 1-desk 2 comparison, with participants having a mean difference of -0.21 mm Hg in systolic blood pressure and 0.09 in diastolic. But, the improper arm positions had significant effects on the readings. Lap arm position resulted in a mean increase of 4 mm Hg in both systolic and diastolic readings. Side arm position led to systolic readings that were 6.5 mm Hg higher and diastolic readings that were 4 mm Hg higher. For those with high blood pressure readings—about 36 percent of the participants—the wrong arm position caused yet higher readings, with systolic readings about 9 mm Hg higher than desk readings.

The authors speculate that simple physiological mechanisms likely explain the increase in blood pressure when the arm is lower than the heart—more gravitational pull, compensatory constriction of blood vessels, and muscle contraction may lead to higher pressure. As for why health care providers are known to sometimes use these wrong arm positions, it may be a lack of awareness, training, equipment, and/or resources.

The authors of the study call for more training and education about proper blood pressure measurements, which are essential for appropriate management of hypertension and prevention of cardiovascular disease.

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