Sensitivity of pulmonary crackle parameters to filter cut-off frequency.

Pulmonary crackles are very important indicators in the diagnosis of pulmonary disorders. Parameters derived from their waveforms, such as initial deflection width and two-cycle duration width, are useful in classifying a crackle and correlating it with various disorders. To obtain a crackle waveform, the background vesicular sound is filtered out and the crackle parameters are very sensitive to filter cut-off frequency. In this study, sensitivity analysis of waveform parameters of simulated crackles superimposed on real vesicular sound is carried out, emphasizing the necessity of precision in determining the filter cut-off frequency.