I'm a fan of automatic arm blood pressure monitors like the Omron HEM series. Most of the time, people appreciate the sense of control and assurance these machines provide. And occasionally, the rare severe case of white coat hypertension will be unmasked. For example, some people have systolic pressures of 180s in the office and 120s at home. So if their medications are increased to treat the high blood pressure in the office, then at home, they pass out from low blood pressure. Blood pressure monitors are enormously helpful in these and other cases.
But rarely, the opposite happens. The occasional person is so unnerved by the blood pressure monitor that it actually causes their blood pressure to increase. Seeing the high reading, in turn, causes them to panic, and they press the button again and again to take more readings, becoming more and more panicked, which in turn causes the pressure to rise even more. This usually results in a frantic phone call.
To try to prevent this from happening, I tell people to take their blood pressure only once after sitting quietly for five minutes. This usually solves the problem.
(As a related aside, Hilarious Journal Article #8 is a letter in the New England Journal of Medicine titled "An Acute Hypertensive Episode Triggered by an Ambulatory Blood-Pressure-Monitoring Device.")
Link: Patient Information on High Blood Pressure
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