[Pulmonary crackles, what does the clinician hear?]

The overall duration of a pulmonary crackle is usually less than 20-30 ms but psychoacoustics demonstrates that an acoustical event with a duration of less than 20-40 ms cannot be estimated in terms of pitch and duration. We pose the hypothesis that the main resonant information is contained into the breath sounds following the crackle.

Eight patients with COPD, viral pneumonia, bronchiectasis, congestive heart failure, hypoproteinemia and fibrosing alveolitis were recruited for this study. Thirty-six crackles were analyzed in time and frequency domains; 12 in each category of low, medium and high frequencies. The acoustic features of the crackles, their segments (initial deflection width, first cycle duration, two cycles duration, decay segment) and the breath sounds following the crackles were compared.

The study confirms the differences between the three crackles categories in time and frequency domains. No statistical differences were found between the decay segments and breath sounds in each category.

Breath sounds modified by lung tissue density could be the main resonators determining the fundamental transmission frequencies of crackle signals. Combined acoustic analysis of crackles and breath sounds could replace single analysis of isolated crackles.