An acoustic model of the respiratory tract

With the emerging use of tracheal sound analysis to detect and monitor resp iratory tract changes such as those found in asthma and obstructive sleep a pnea, there is a need to link the attributes of these easily measured sound s first to the underlying anatomy, and then to specific pathophysiology, To begin this process, we have developed a model of the acoustic properties o f the entire respiratory tract (supraglottal plus subglottal airways) over the frequency range of tracheal sound measurements, 100 to 3000 Hz, The res piratory tract is represented by a transmission line acoustical analogy wit h varying cross sectional area, yielding walls, and dichotomous branching i n the subglottal component. The model predicts the location in frequency of the natural acoustic resonances of components or the entire tract, individ ually, the supra and subglottal portions of the model predict well the dist inct locations of the spectral peaks (formants) from speech sounds such as /a/ as measured at the mouth and the trachea, respectively, in healthy subj ects. When combining the supraglottic and subglottic portions to form a com plete tract model, the predicted peak locations compare favorably with thos e of tracheal sounds measured during normal breathing. This modeling effort provides the first insights into the complex relationships between the spe ctral peaks of tracheal sounds and the underlying anatomy of the respirator y tract.