Spatial representation of thoracic sounds

Simultaneous multi-microphone recordings of thoracic sounds on the chest wall contain spatial information of potential diagnostic value. To begin to access this information, an algorithm was developed to spatially represent these sounds. For every point within the thorax the algorithm tests the hypothesis that it contains the only relevant acoustic source. A hypothetical source signal is calculated by a least squares estimation procedure to explain a maximum of the signal variance in all microphone signals. The explained fraction of the total microphone signal variance is then displayed as a function of space in a 5-dimensional, gray-coded image. The algorithm was preliminarily evaluated using 16-microphone recordings from two healthy male subjects. Inspiratory and expiratory breath sounds as well as first and second heart sounds were analyzed separately. The images show distinct patterns for inspiratory breath sounds, expiratory breath sounds and heart sounds and similar images were obtained for a given sound category for both subjects. These representations are consistent with the assumed origin of the analyzed sounds. Specifically, the images support the concept that inspiratory sounds are produced predominantly in the periphery of the lung, while expiratory sounds are generated more centrally