Spectral analysis of cough sounds of patients with COVID-19

Cough is a frequent manifestation  of COVID-19  (COronaVIrus Disease 2019), therefore,  it has an important  diagnostic value. There is little information  about the characteristics  of cough of COVID-19  patients in the literature.  To perform a spectral analysis of cough sounds in COVID-19 patients in comparison  with induced cough of healthy individuals. Methods. The main group consisted of 218 COVID-19  patients (48.56% – men, 51.44% – women, average age 40.2 (32.4; 50.1) years). The comparison group consisted of 60 healthy individuals (50.0% men, 50.0% women, average age 41.7 (31.2; 53.0) years) who were induced to cough. Each subject had a cough sound recorded,  followed by digital processing using a fast Fourier transform algorithm. The temporal-frequency parameters of cough sounds were evaluated: duration (ms), the ratio of the energy of low and medium frequencies (60 – 600 Hz) to the energy of high frequencies (600 – 6 000 Hz), the frequency of the maximum sound energy (Hz). These parameters  were determined  in relation  to both the entire cough and individual phases of the cough sound. Results. Significant differences were found between some cough parameters  in the main group and in the comparison  group. The total duration  of the coughing act was significantly shorter in patients with COVID-19, in contrast to the induced cough of healthy individuals (T = 342.5 (277.0; 394.0) – in the main group; T (c) = 400.5 (359.0; 457.0) – in the comparison  group; p = 0.0000). In addition,  it was found that the cough sounds of COVID-19  patients are dominated by the energy of higher frequencies as compared  to the healthy controls (Q = 0.3095 (0.223; 0.454) – in the main group; Q (c) = 0.4535 (0.3725; 0.619) – in the comparison  group; p = 0.0000). The maximum frequency of cough sound energy in the main group was significantly higher than in the comparison  group (Fmax = 463.0 (274.0; 761.0) – in the main group; Fmax = 347 (253.0; 488.0) – in the comparison  group; p = 0.0013). At the same time, there were no differences between the frequencies of the maximum energy of cough sound of the individual phases of cough act and the duration of the first phase. Conclusion. The cough of patients with COVID-19 is characterized  by a shorter duration and a predominance of high-frequency energy compared to the induced cough of healthy individuals.