Modelling and simulation of a vibrating membrane for the acquisition of lung sounds

The lack of general doctors and physicians represents the main problem for most of the modern national health systems. The high operating and maintenance costs of hospitals and clinics complete the critical picture. The development of new diagnostic tools can play a fundamental role in tackling these challenges. Recent studies have shown that electronic stethoscopes can raise the diagnostic suspicion of several pulmonary diseases, for instance interstitial lung diseases. The vibrating membrane, or diaphragm, is a fundamental component of the stethoscope that significantly affects its performance. Despite several theoretical and experimental studies are available about membrane vibration, the exact role of the diaphragm in a stethoscope for the acoustic coupling is still mostly unclear. In this paper we investigate the effect of the diaphragm on the sensibility and bandwidth of electronic stethoscopes. We setup a 1D numerical simulation of the system composed by the lung, human body, vibrating membrane and microphone. The parameters are devised from breathing mechanics and from the datasheets of a commercial diaphragm and microphone. The performance predicted by numerical simulations have been compared to experimental measurements on our prototype of electronic stethoscope. In particular, the predicted pressure at the input of the microphone is very close to that experimentally measured during outpatient visits at the University Hospital of Modena (Italy).