'Slide whistle' breath sounds: acoustical correlates of variable tracheal obstruction

We report a case of a man who developed severe shortness of breath and the finding of breath sounds that rose in frequency during inspiration and fell during expiration. These unusual sounds were caused by a spherical tumour arising from the main carina that nearly completely obstructed the distal trachea. The frequency variation disappeared after the removal of the mass. We evaluated this phenomenon using a modelling technique that we had previously developed to analyse the human airways as acoustical tubes. This analysis revealed that the acoustical conditions in the trachea were substantially modified by the presence of the solid mass as the trachea slightly dilated during inspiration, partially relieving the obstruction. Most of the anomalous characteristics of the breath sounds could be explained using this model. We conclude that a detailed understanding of the acoustic conditions of the airways allows correlation with anatomical and physiological conditions and may be of use in diagnosis or evaluation of the airways in health and disease.