Abstract
The onset and development of many airway pathologies affect sound propagation throughout the respiratory system; changes in respiratory sounds are detected primarily by auscultation, which is highly skill dependent. The aim of the present study was to compare healthy and asthmatic pulmonary acoustics by applying a 1D model of wave propagation on CT-based patient-specific geometries. High-resolution CT lung images were acquired in five healthy volunteers and five asthmatic patients at total lung capacity (TLC) and functional residual capacity (FRC). Tracheobronchial trees were reconstructed from CT images. Acoustic pressure, impedance and wall radial velocity were measured by simulating acoustic wave propagation of two external, acoustic pressure waves (1 Pa, 200 and 600 Hz) from the trachea level to the 4th generation. In asthmatic patients, acoustic pressure averaged across the last three generations showed a reduction equal to 29.7% (p<0.01) at FRC, at 200 Hz; input and terminal impedance were 34.5% (p<0.05) higher both at FRC and TLC; wall radial velocity was more than 80% (p<0.05) lower in higher generations both at FRC and TLC. Airway differences in asthma alter acoustic parameters at FRC and TLC, with the greatest difference at FRC and 200 Hz. Acoustic wave propagation analysis represents a quantitative approach that has potential to objectively characterize airway differences in individuals with diseases such as asthma.
Highlights
Auscultation has been used by clinicians for hundreds of years to qualitatively diagnose and monitor the progression of pulmonary pathologies
The results showed that the acoustic parameters were sensitive to the airways alterations induced by the asthma pathology, both at functional residual capacity (FRC) and total lung capacity (TLC)
This study provides an insight to the acoustic properties of the airways and to the alterations induced by the asthma condition, by simulating an insonification experiment at the level of the trachea
Summary
Auscultation has been used by clinicians for hundreds of years to qualitatively diagnose and monitor the progression of pulmonary pathologies. Auscultation technique is based on the clinical evidence that the morphological and functional alterations of the respiratory system result in measurable changes in sound generation and propagation [1]. Suki et al.[3] and Jackson et al [4,5] studied the frequency dependency of acoustic impedance of the subglottal respiratory tract. Henry et al [13] further extended the approach in [8,14] to account for image-based geometries in healthy subjects and proposed a simplified approach to specific pathological conditions. We applied the analytical model developed by Henry et al [13] to study the sound propagation in real tracheobronchial trees reconstructed from CT data in healthy and asthmatic subjects
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