Bell or diaphragm in the measurement of blood pressure?

BACKGROUND: International guidelines have given diverse recommendations as to which side of the stethoscope should be used in the measurement of blood pressure. OBJECTIVE: To determine if there is any difference between the bell and the diaphragm sides of the ordinary acoustic stethoscope in the measurement of blood pressure. DESIGN AND METHODS: We compared, in random order, the bell and the diaphragm side of the ordinary acoustic stethoscope and also the effect of low- and high-frequency amplification with an electronic stethoscope in the measurement of blood pressure, in 250 adults. SETTING: Department of Medicine, Turku University Central Hospital. RESULTS: No statistically significant difference was seen between the bell side and the diaphragm side of the acoustic stethoscope, either in systolic blood pressure (SBP; mean +/- SD 129.5 +/- 21.7 and 129.4 +/- 20.8 mmHg, respectively) or diastolic blood pressure (DBP; 77.0 +/- 12.0 and 77.1 +/- 12.0 mmHg, respectively). Both the low-frequency (130.7 +/- 22.5 mmHg) and the high-frequency (131 +/- 22.2 mmHg) amplification of systolic Korotkoff sounds yielded significantly greater values of SBP than were measured either with the bell (P = 0.008 compared with low frequency, P = 0.0005 compared with high frequency) or the diaphragm (P = 0.004 compared with low frequency, P = 0.0001 compared with high frequency). Low-frequency amplification of DBP (76.4 +/- 12.3 mmHg) yielded values significantly lower than those measured with the bell (P = 0.04) or the diaphragm (P = 0.01). Values from high-frequency amplification of DBP (77.2 +/- 12.3 mmHg) did not differ significantly from those measured with the acoustic stethoscope. CONCLUSIONS: Both sides of the acoustic stethoscope give similar results in the measurement of office blood pressure and either side can be used in the reliable measurement of blood pressure.