Detecting regional lung properties using audio transfer functions of the respiratory system

In this study, a novel instrument has been developed for measuring changes in the distribution of lung fluid the respiratory system. The instrument consists of a speaker that inputs a 0 - 4 kHz White Gaussian Noise (WGN) signal into a patient´s mouth and an array of 4 electronic stethoscopes, linked via a fully adjustable harness, used to recover signals on the chest surface. The software system for processing the data utilizes the principles of adaptive filtering in order to obtain a transfer function that represents the input - output relationship for the signal as the volume of fluid in the lungs is varied. A chest phantom model was constructed to simulate the behavior of fluid related diseases within the lungs through the injection of varying volumes of water. Tests from the phantom model were compared to healthy subjects. Results show the instrument can obtain similar transfer functions and sound propagation delays between both human and phantom chests.