Toward a Smart Stethoscope: Correlation between trachea internal airway geometry and the auscultation signal response*

Stethoscope for human auscultation represents an easy and prompt tool for physicians to diagnose rapidly the existence of a pulmonary disease. However, the physics that stands behind the generation of acoustic signals and the internal geometry of the trachea or lung airways has not been clearly defined. In our project, we started to tackle the problem using a microphone, and instead of carrying out experiments on human beings, we chose to use a 3D-printed trachea model based on geometry data collected from a real human patient. Our main purpose is to understand how the geometry of the trachea wall interacts with the air flow and thus, impacts the acoustic signal generated and acquired by the microphone. To carry out our experimental measurements, we use an artificial air pump to simulate the respiratory process in the 3D-printed trachea mounted in an anechoic chamber. The acoustic signal is conditioned and low-pass filtered at 3000 Hz, then processed using a Labview based data acquisition sysyem. The signal is then analyzed using spectral analysis methods as implemented in Liu and Katz (2013, J of Fluid Mech., 728, 417:57) to establish the correlation between the tracheal acoustic signal and its internal geometry.