Simulation, Design and Prototyping of a Diaphragm for the Acquisition of Lung Sounds

This paper investigates the effect of diaphragm on the sensitivity and bandwidth of electronic stethoscopes. The analyzed system includes the lung, human body, diaphragm, and microphone. A simulation framework was developed using parameters devised from respiratory mechanics, commercial components and practical characterizations. Numerical simulations were compared to experimental data collected with the electronic stethoscope prototype we developed. The predicted pressure at the microphone closely matched the experimental measurements carried out during outpatient visits at the University Hospital of Modena (Italy). All the human subjects involved in these measurements were volunteers and gave their informed consent. Based on the simulation results, we designed a diaphragm optimizing bandwidth and gain. Interestingly, the optimal configuration weakly depends on the damping factor. In fact, bandwidth and gain of the frequency response function of the system are affected by less than 1% if the damping factor is changed over ±3 orders of magnitude around the optimal value. A prototype has been produced in ONYX® material under the optimal configuration. The prototype is 3D-printed in a single block composed of a central disc capturing and transferring vibration waves, a suspension that links the central disc to the outer ring and a joint to fix the diaphragm to the stethoscope body. The predicted mechanical characteristics are Young modulus of 2.4 GPa and density of 1200 Kg/m3.Clinical Relevance- The shortage of general doctors and physicians is a major issue for modern healthcare systems, as well as high facility and maintenance costs, prevent the wide diffusion of advanced medical test laboratories. The development of new and cheap diagnostic tools is crucial to address these challenges. By developing this application and refining the vibrating membranes, which act as the 'ear' of the stethoscope, it will be possible to reliably and early detect pulmonary diseases directly through auscultation. This would eliminate the need for specialized visits, which require professionals not always available in the field, as well as highly expensive equipment that is not universally accessible, particularly in less affluent regions. Recent studies showed that electronic stethoscopes can improve the capability of detecting pulmonary diseases, such as interstitial lung diseases. Indeed, the diaphragm (or membrane) is a fundamental component of stethoscopes and plays a significant role in its performance, although its exact influence on acoustic coupling remains mostly unclear.