Differences of Blood Pressure Measurement Between Mercury Sphygmomanometer and Electronic Devices

Abstract

Background: The prognostic significance of ideal blood pressure (BP) control in hypertensive patents was well established. In hypertensive patients, reduction of diastolic BP by 5-6 mmHg would reduce 35-40% risk in stroke, and 20-25% of risk in coronary heart disease. Therefore, accurate BP measurement in the daily practice is crucial. Electronic sphygmomanometers provide convenience but their accuracy had been debated extensively. The purpose of this study was to compare the accuracy of three different brands of electronic sphygmomanometers with the mercury sphygmomanometer, so that we can balance the convenience and accuracy in outpatient clinic. Methods: In 2002, we recruited subjects who visited Department of Family Medicine, Taipei Veterans General Hospital, and Taipei Municipal Yang Ming Hospital for study. Every individual took BP measurements, irrespective of underlying diseases, by mercury sphygmomanometer and three other different electronic devices at 2-minute interval. Comparisons of the measurement data were done by student’s t test and Pearson correlation. Results: In total, 60 subjects (mean age: 69.9±12.6 years, 52 males and 8 females) were recruited. The mean reading of mercury sphygmomanometer was 125.8±18.7 mmHg for systolic BP (SBP) and 75.5±1 0.4 mmHg for diastolic BP (DBP). SBP readings of three different electronic devices were 128.6±18.4 mmHg, 129.3±17.1 mmHg, and 126.0±20.2 mmHg, respectively. Readings of DBP were 72.9±1 0.6 mmHg, 69.5±12.0 mmHg, and 72.7±10.4 mmHg, respectively. DBP readings taken by electronic devices were significantly lower than mercury sphygmomanometer (p=0.01 8, p＜0.001, and p=0.003 respectively); the SBP readings by electric devices were all higher than mercury sphygmomanometer, but only one achieved statistical significance (p=0.094, p=0.006, and p=0.852, respectively). Good correlation was observed between electronic devices and the mercury sphygmomanometer in both SBP (correlation coefficient were 0.76, 0.86, and 0.84, respectively; p all ＜0.05) and DBP (correlation coefficient was 0.69, 0.56, and 0.78, respectively; p all ＜0.05) readings. Conclusion: The consistency of BP measurements between electronic devices and the mercury sphygmomanometer was confirmed. However, the BP readings from electronic devices tended to be lower in DBP and higher in SBP. A careful calibration of the pressure sensor inside the electronic devices may help to overcome the difference of measurement.