An experimental study on the role and function of the diaphragm in modern acoustic stethoscopes

Vibrations of a diaphragm of an acoustic stethoscope in contact with the body of an auscultated patient are the source of the sound transmitted to the ears of a physician performing examination. Mechanical properties of a diaphragm are supposed to significantly affect the parameters of the transmitted bioacoustic signals. However, the exact relation remains mostly unclear, as the underlying phenomena involve complex effects of acoustic coupling between the diaphragm and the body of a patient. The present study introduces a detailed methodology for determining vibroacoustic behavior of a diaphragm of a stethoscope during an auscultation examination. A laser Doppler vibrometer is used to measure the velocity of various points on the surface of a diaphragm during heart auscultation. Synchronized recordings of electrocardiography signals are used for segmentation. Representative data sets are selected and analyzed for various kinds of diaphragms. The results show significant differences in vibration velocity levels and their distribution across the surfaces of the considered structures. In this regard, it is also shown that the currently available solutions can be significantly improved by using structures better matched to the acoustic impedance of a body.