Discovering new facts and revealing existing myths about the acoustic stethoscope 200 years after its invention

Acoustic stethoscope, invented exactly 200 years ago by French physician, Rene Laennec, is the most widespread medical diagnostic device, and also the icon of the medical profession. Hence, it might seem strange, that the mechanisms and physical phenomena underlying the auscultation examination are still not well understood, and some of the commonly repeated statements – such as those regarding highor low-pass filtering effects supposedly introduced by specific kinds of chestpieces – have no scientific justification. The present study introduces results of the experimental investigations on the different factors influencing the acoustic properties of a stethoscope. Unlike other studies which were based either on subjective evaluation of sound quality or on measurements of the transfer functions performed using loudspeakers as the primary sound source, the investigations described herein were based on original experimental and data analysis schemes, which allowed to quantitatively evaluate the parameters of signals recorded during the actual auscultation examinations. Results obtained using various kinds of chestpieces and different lengths of the hollow tubes are compared in order to expose the factors which have the greatest impact on the perceived sound quality. It is shown, that the parameters and the construction of the chestpiece determine the achievable sound level, while the hollow tubes act as an acoustic filter. This contradicts the statements repeated in the literature for over 50. years, about the highly frequency-selective behaviour of the diaphragms of the stethoscopes.