What can cause an inaccurate blood pressure reading during measurement?

An inaccurate blood pressure reading can occur when the patient's arm is positioned above the level of the heart. This positioning can lead to an artificially low measurement because gravity can affect the blood flow and pressure readings. When the arm is elevated, the hydrostatic pressure differs, causing the reading to drop compared to the true blood pressure.

In contrast, the other factors mentioned contribute to proper measurement techniques. When the cuff deflates at a constant, steady rate, it allows for a more accurate detection of systolic and diastolic pressures. Centering the cuff bladder over the brachial artery ensures that the measurement captures the blood pressure effectively at the right site. Calibrating the aneroid needle to zero is essential for accurate readings, as it ensures the baseline is correct before measuring blood pressure. All these practices enhance the accuracy of the blood pressure reading, making arm elevation the significant factor that can lead to inaccuracy.