Observer Factors in the Measurement of Blood Pressure

GRAPHIC records of human blood pressure . measurements present a striking picture. The wide fluctuations among the recorded levels give the impression that human arterial blood pressure is a very variable biological phenomenon. It has long been recognized that this is true; the blood pressure of human beings responds readily both to internal physiological conditions and to external stimuli. In spite of this, it is logical to assume that the variability seen in recorded measurements of blood pressure does not reflect merely fluctuations in the blood pressure itself. Accurate and precise measurement of blood pressure is not necessarily readily accomplished, particularly by the indirect or clinical method; some of the recorded variability must certainly result from errors of measurement. Such errors arise from two sources: (1) the instrument used and (2) the observer.