Relationship between airflow and normal lung sounds

The relationship between airflow and respiratory sounds has always been of particular interest for diagnostic purposes. We investigated the relationship between airflow and lung sounds. Respiratory lung sound signals with the corresponding airflow signals from ten healthy subjects were studied. The lung sounds and the corresponding airflow signals were sequested to 100 ms segments with 50% overlap between successive segments. The mean lung sound amplitude (meanAMP) of the time signal as well as the average power (P_aνg) of the sounds between 100-300 Hz arid the corresponding mean airflow were calculated for each segment. The following five models were studied: linear relationship between meanAMP and flow (model 1), linear relationship between meanAMP and flow² (model 2), linear relationship between P_aνg and flow (model 3), linear relationship between log(P_aνg) and flow (model 4) and linear relationship between log(P_aνg) and log(flow) (model 5). Linear regression analysis was used to investigate these relationships using the upper 15% of flow signal in each inspiration and the corresponding meanAMP and P_aνg. The correlation coefficient (r) between the model variables for each subject in each model was calculated. Also the RMS error between the regression line and the actual data for each model was averaged among the subjects. The results showed that the experimental data fits the model 3 very well. Therefore, we suggested a linear relationship between P_aνg and flow: P_aνg=a_*flow+b. This model can be chosen to estimate airflow from the average power of lung sounds.