If the arm is below heart level during BP measurement, the reading tends to be:

• A. More accurate
• B. Falsely high
• C. Falsely low
• D. Unreliable

Answer: (B)

The key idea here is that the position of the arm relative to the heart changes the pressure you measure due to hydrostatic effects. When the arm is below heart level, gravity adds to the arterial pressure in the arm, so the cuff ends up reading a higher pressure than the true arterial pressure. That’s why the reading tends to be falsely high. If the arm were above heart level, the reading would tend to be falsely low, and with the arm at heart level the measurement is most accurate. So the best choice is that the reading is falsely high when the arm is below heart level. To get an accurate result, keep the arm supported at heart level, with the patient seated and both feet uncrossed.