What is the effect of having the arm below heart level during BP measurement?

• A. It can produce falsely high readings.
• B. It can produce falsely low readings.
• C. It has no effect.
• D. It speeds up the measurement.

Answer: (D)

Having the arm below heart level changes the BP reading because gravity adds hydrostatic pressure to the blood column in the arm. This makes the cuff experience a higher pressure than the true arterial pressure, so the measurement appears falsely elevated. In practice, BP should be taken with the arm supported at heart level to obtain an accurate value; for every centimeter the arm is below the heart, the reading can rise by about 0.7–0.8 mmHg (roughly 7–8 mmHg for ~10 cm). If the arm were above heart level, the reading would tend to be falsely low. The position of the arm does not speed up the measurement; the speed depends on the cuff deflation rate and technique.