Band-Pass Spectral-Temporal Parameters of Forced Expiratory Noises in Bronchial Obstruction. Relation with Whistling Sounds

A comparative study of band-pass spectral-temporal parameters of tracheal noises of forced expiratory (FE) and quantitative assessment of FE wheezes was conducted on an experimental sample including patients with bronchial obstruction (asthma and COPD, n = 36) and healthy asymptomatic individuals with normal lung function (n = 39). Digital processing of tracheal noise signals was performed in MATLAB automatically using a specially developed algorithm. The analyzed acoustic band-pass parameters are temporal and spectral characteristics in several (2 to 6) combined 200-Hz bands, divided into mid- (200-800 Hz) and high-frequency (800-2000 Hz) areas in the range of 200-2000 Hz, as well as their ratios. FE wheezes were recognized by an experienced operator on spectrograms in the SpectraPLUS audio editor. A significant predominance of the values of high-frequency bandpass energy parameters of tracheal noises and the ratio of energies and powers of the high-frequency and mid-frequency ranges was revealed in patients with obstructive pulmonary diseases compared to healthy controls. The number of whistling sounds was greater in patients and moderately correlated with the acoustic parameters. Redistribution of acoustic energy to the high-frequency region is probably associated with the pathophysiological basis of bronchial obstruction - narrowing of the conducting airways and an increase in airflow resistance.