Assessment of the relationship between tracheal breathing sounds and lung ventilation during physical exercise

Introduction. Assessment of the functional state of the respiratory system is a relevant task in the fields of sports, aerospace, and maritime medicine. Direct flowmetry methods cannot always be applied under conditions of a sealed enclosed environment. The recording and analysis of lung sounds appears to be a promising method for assessing the state of the respiratory system.

Objective. To assess the relationship between the amplitude characteristic of the recorded lung sound signal and the magnitude of pulmonary ventilation, as well as the applicability of the acoustic method for assessing the respiratory rate in healthy individuals during physical exercise, regardless of age and sex.

Materials and methods. The study involved 25 volunteers (20 male and 5 female) aged 23–59 years (mean age 35.5 ± 8.7 years). The participants were subjected to a stepwise increasing workload on an Ergoselect 200P cycle ergometer (Ergoline GmbH, Germany) up to submaximal heart rate levels, with simultaneous recording of respiratory sounds over the extrathoracic section of the trachea and measurement of respiratory flow via direct flowmetry using a Jaeger Oxycon Pro device. Statistical data processing was performed using the Statistica 13 software (StatSoft Inc., USA). To assess the relationship between respiratory sound power and pulmonary ventilation, a correlation analysis was conducted using Spearman’s rank correlation coefficient (r_s).

Results. During the study, the achieved maximum power output for all participants ranged 105–240 W; only two subjects were capable of developing a power level exceeding 210 W. Dependencies of respiratory sound power on pulmonary ventilation were obtained. Spearman’s rank correlation coefficient between the studied parameters was 0.58 (p < 0.001). Significant changes in the mean power of respiratory sounds were observed with an increase in load and pulmonary ventilation, already at the 30 W stage compared to the resting state (0 W) (p < 0.0001). The power of tracheal respiratory sounds also increased by 56% between the 120 W and 135 W load stages (p = 0.023) and by 75% between the 180 W and 195 W load stages (p = 0.043). No significant differences were found between respiratory rate assessments obtained by direct flowmetry and acoustic methods.

Conclusions. A statistically significant, moderate positive correlation was established between the magnitude of pulmonary ventilation and the mean power of respiratory sounds (r_s = 0.58; p < 0.001). For pulmonary ventilation values up to 60 L/min, the relationship between the mean power of tracheal sounds and pulmonary ventilation was found to be linear. A satisfactory agreement was determined between the acoustic assessment of respiratory rate and the data obtained by direct flowmetry methods. The analysis of respiratory sounds is capable of providing an indirect assessment of the state of the respiratory system.

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