On the issue of cough sound spectral features in patients with chronic bronchitis

Cough is the main symptom of chronic bronchitis, and the cough sound may be an important diagnostic tool. However, there is no data in the literature on the characteristics of cough sounds in patients with chronic bronchitis (CB). Objective. To perform a spectral analysis of cough sounds from patients with chronic bronchitis, in comparison to cough sounds from patients with asthma, COPD, and COVID-19, as well as induced cough from healthy individuals. Material and methods. The main group consisted of 63 patients with exacerbation of CB (46.0% — men, 53.9% — women; the middle age — 48.4 [47; 49] years). The comparison groups consisted of patients with asthma (n=20), COPD (n=20), COVID-19 (n=20) and healthy individuals (n=20). Cough sounds were recorded from each subject. The time-frequency parameters of sounds were analyzed using the fast Fourier transform of the entire cough episode and its separate phases: duration (ms) (T, T1, T2, T3), the ratio of low and medium frequency energy (60—600 Hz) to high frequency energy (600—6000 Hz) (Q, Q1, Q2, Q3), the frequency of maximum sound energy (Hz) (Fmax, Fmax1, Fmax2, Fmax3). Results. It was found that there were significant differences in cough parameters between the main group and comparison groups. Thus, the total duration of CB cough turned out to be longer than in patients with COVID-19. T1 and T3 were longer than in all comparison groups, and T2 was shorter than in patients with asthma, COPD and healthy individuals. Overall, cough episodes in patients with CB had a predominance of low-frequency energy compared to asthma and high-frequency energy compared to induced cough in healthy individuals. During the first and third phases of cough in CB patients, low-frequency energy predominated. In the second phase of cough, low-frequency energy also predominated when comparing CB with asthma, while high-frequency energy was more prevalent when comparing it with COPD patients. Fmax and Fmax1 were significantly lower in patients with CB compared to those with asthma. Fmax2 was lower in patients with CB than in asthma patients and higher compared to the induced cough of healthy individuals. Fmax3 was significantly lower in patients with CB compared to all other groups. A comparative analysis of cough in CB patients and COVID-19 patients has revealed significant differences in the duration of the cough episode, as well as in the first and third phases of cough. Cough in CB lasts longer than in COVID-19, and the frequency of cough sounds is lower. The maximum frequency of sound energy is lower in CB compared to COVID-19. Conclusions. The cough of patients with CB has significant differences in its main time-frequency characteristics when compared to the cough sound of patients with asthma, chronic obstructive pulmonary disease (COPD), and COVID-19. These differences may indicate that spectral tussophonobarography could be useful in the diagnosis and differential diagnosis of chronic bronchitis.