Effect of stethoscope position on auscultatory blood pressure measurement

When measuring blood pressure (BP) using the auscultation method, a stethoscope is commonly used. In clinical practice, it is sometimes placed under the cuff, but more usually outside the cuff on the antecubital fossa. However, there is little scientific evidence to quantify the BP difference between the BP measurements taken with the stethoscope under the cuff or outside the cuff. The aim of this study was to provide these data. Nine healthy subjects were studied, and there were two repeated measurements for each subject. Two electronic stethoscopes (one under the cuff, the other outside the cuff) were used to record the Korotkoff sounds. The signals of cuff pressure and two Korotkoff sounds were simultaneously recorded to a computer for off-line analysis. The sounds recorded from the two positions were then replayed to two operators to determine systolic and diastolic BPs (SBP and DBP). The BP difference from the two positions was finally quantified. Variance analysis showed that there was no significant BP difference (for both SBP and DBP) between the repeat measurements and between the two operators (p>0.1). There was also no significant SBP difference between results with the stethoscopes placed at the two positions (P>0.1). However, a significant difference for DBP was observed, with a mean±SD difference of -3.0±1.4 mmHg (P<;0.001). In conclusion, this study quantified the effect of stethoscope position on BP measurement.