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Hypertension/High Blood Pressure Health Center

Drugstore Blood Pressure Machines May Not Be Dependable

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May 18, 2000 -- For people who routinely depend on drugstore machines to monitor their blood pressure, a Florida physician has a bit of advice -- don't -- especially if you are larger or smaller than average. When it comes to automated blood pressure machines, one-size arm cuff doesn't really fit all.

In a study reported in the May issue of The Journal of Family Practice, researchers found a big difference among blood pressure readings received by different-sized people who visited 25 pharmacies in Central Florida.

"We found that automated blood pressure machines ... did not meet accepted standards of accuracy and reliability of measurement," writes lead researcher Daniel J. Van Durme, MD. "Although further study in this area may be useful to strengthen this recommendation, we recommend that patients not rely on the results of in-store automated blood pressure devices."

Blood pressure is the force of the blood pushing against the walls of arteries each time the heart beats. When the heart contracts and pumps blood, the pressure it exerts on blood vessel walls is called systolic pressure. The pressure on the vessel walls between beats is called diastolic pressure. Blood pressure is always given as these two numbers, the systolic and diastolic pressures. Usually, they are written one above the other, such as 120/80 mm Hg, with the top number the systolic pressure, and the bottom the diastolic pressure.

For people with a small arm size, systolic measurements were on average 10 mm Hg higher than readings taken right after by a clinician with a portable mercury manometer, another instrument used to measure blood pressure. Diastolic pressure readings averaged 9 mm Hg higher.

For people with a larger than normal arm, diastolic readings averaged 8.3 mm Hg lower than the clinician's measurements, but systolic readings were not that different.

Readings for the person with an average arm diameter were not significantly different between the store readings and the clinician's test, but Van Durme says average-sized people should not depend on the accuracy of the machines.

"Even patients with a medium-sized arm can expect significant and unacceptable variability in blood pressure readings," Van Durme writes. Van Durme is a physician in the department of family medicine and the division of cancer control at the University of South Florida.

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