Errors in the measurement of blood pressure

The effect of posture on blood pressure measurement in pregnant and non-pregnant subjects was studied. In non-pregnant patients undergoing cardiac catheterization, central blood pressure remained unaltered with a change from the supine to the lateral position. However in all subjects studied, an apparent decrease in both systolic and diastolic blood pressure occurred when measured in the upper arm in the lateral position. This fall is artifactual and does not represent a change in blood pressure. It is concluded that blood pressure measurements in the lateral position are inaccurate.