Estimation of the site of wheezes in pulmonary emphysema: airflow simulation study by the use of A 4D lung model.

Adventitious lung sounds in pulmonary emphysema, wheezes, are continuous musical sounds during expiration with 400 Hz or more. The textbook tells that expiratory airflow limitation in emphysema occurs at the peripheral airways and that wheezes are generated there. We have recently proposed a novel hypothesis based on image analysis and theoretical consideration that expiratory airflow limitation in emphysema occurs at the intra-mediastinal airway (trachea, main bronchi, and right lobar bronchi) due to compression by overinflated lungs. We performed expiratory airflow simulation by the use of a 4D finite element lung model, and found periodical vortex release with 300-900 Hz at the end of protrusion of the the tracheal posterior wall. Relationship between the peak frequency of pressure fluctuation and airflow velocity was in agreement with Strahal's law either in normal or emphysematous condition. Contrarily, airflow simulation in a small bronchus (1.5 mm in diameter) indicated no apparent periodic vortex release.