Placing crackles on the flow-volume plane: a study of the relationship between the time position, the flow and the volume.

The aim of this study was to analyse inspiratory crackles in patients with Pulmonary Fibrosis (PF) and Bronchiectasis (BE). One case of Chronic Obstructive Pulmonary Disease (COPD) has also been included. The relationships between the time of occurrence of crackles (T) in the breath cycle and the corresponding flow at the mouth (F) and volume (V) have been investigated. The linear correlations between the flow, volume and time have been investigated by Pearson's R-test and the same variables have been analysed by Principal Component Analysis (PCA) in order to verify the effective dimension of these data. The results show a strong correlation between the time of occurrence and the volume in all the examined cases. PCA shows that in all cases F and V account for more than 90% of variation. These results suggest that placing crackles on the flow-volume plane does not cause loss of information.