Compared with arm cuffs, how reliable are home BP monitors that fit on the wrist or even the finger? And why aren’t BP readings the same in both arms?
—Bernard Wolf, MD, Concord, Calif.

Arm cuffs appear to be the most reliable at-home devices. Some wrist cuffs, such as one by Omron, have been validated, but I still am reluctant to recommend them because readings might be affected by how the patient positions his arm and possibly by the anatomy of the wrist. Finger cuffs, which have not been validated, are good for studies looking at beat-to-beat change in BP, but these devices have not been validated for home use. I generally recommend the automated device rather than manual measurement because automated devices are accurate and avoid manipulations required of the patient that could affect the readings. One would expect BP readings to be the same in both arms, and they usually are.

The problem is that BP varies continuously from moment to moment, and unless the BP is measured simultaneously in both arms, there will always be a random difference. A consistent difference is seen if, for example, the right arm is always checked first and the left arm second, caused by an order effect rather than by a true difference between the two arms. Of course, in someone with a stenosis in the axillary or brachial artery, a consistently reproducible difference will be detected.
—Samuel J. Mann, MD (101-9)

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