Computerized Respiratory Sounds Are a Reliable Marker in Subjects With COPD.

BACKGROUND Computerized respiratory sounds have shown potential in monitoring respiratory status in patients with COPD. However, the variability and reliability of this promising marker in COPD are unknown. Therefore, this study assessed the variability and reliability of respiratory sounds at distinct air flows and standardized anatomic locations in subjects with COPD. METHODS A 2-part study was conducted. Part 1 assessed the intra-subject reliability of respiratory sounds at spontaneous and target (0.4-0.6 and 0.7-1 L/s) air flows in 13 out-patients (69.3 ± 8.6 y old, FEV1 of 70.9 ± 21.4% of predicted). Part 2 characterized the inter-subject variability and intra-subject reliability of respiratory sounds at each standardized anatomic location, using the most reliable air flow, in a sample of 63 out-patients (67.3 ± 10.4 y old, FEV1 of 75.4 ± 22.9% of predicted). Respiratory sounds were recorded simultaneously at 7 anatomic locations (trachea and right and left anterior, lateral, and posterior chest). Air flow was recorded with a pneumotachograph. Normal respiratory sound intensity and mean number of crackles and wheezes were analyzed with validated algorithms. Inter-subject variability was assessed with the coefficient of variation, and intra-subject reliability was assessed with the intraclass correlation coefficient (ICC) and Bland-Altman plots. RESULTS Relative reliability was moderate to excellent for normal respiratory sound intensity and mean number of crackles (ICC of 0.66-0.89) and excellent for mean number of wheezes (ICC of 0.75-0.99) at the 3 air flows. Absolute reliability was greater at target air flows, especially at 0.4-0.6 L/s. Inter-subject variability was high for all respiratory sound parameters and across locations (coefficient of variation of 0.12-2.22). Respiratory sound parameters had acceptable relative and absolute intra-subject reliability at the different anatomic locations. The only exception was the mean number of crackles at the trachea, for which both relative and absolute reliability were poor. CONCLUSIONS Respiratory sound parameters are more reliable at an air flow of 0.4-0.6 L/s and are reliable overall at all anatomic locations. This should be considered in future studies using computerized auscultation.