Comparison of stethoscope bell and diaphragm, and of stethoscope tube length, for clinical blood pressure measurement

Thirty-two healthy subjects (19 male and 13 female) were recruited from May to July 2014, with ages from 24 to 68 years. For each subject, there were two repeat sessions with four measurements for each, giving a total of 8 recordings. There was a time interval of at least 1 min between the four measurements within a session and at least 4 min between the two sessions, allowing recovery cardiovascular hemodynamics. The order of the four measurements within the sessions for each subject was randomised. During cuff deflation, the cuff pressure and Korotkoff sounds were digitally recorded at a sample rate of 2,000 Hz. Cuff pressure was linearly deflated at a standard rate of 2-3 mmHg/s. The deflation rate was controlled by an automatic device.