Reliability of crackles in fibrotic interstitial lung disease: a prospective, longitudinal study

Abstract

Background: Although crackles on chest auscultation represent a fundamental component of the diagnostic suspect for fibrotic interstitial lung disease (ILD), their reliability has not been properly studied. We assessed the agreement among respiratory physicians on the presence and changes over time of audible crackles collected in a prospective longitudinal cohort of patients with fibrotic ILD.

Methods: Lung sounds were digitally recorded at baseline and after 12 months at eight anatomical sites. Nine respiratory physicians blindly assessed randomized couples of recordings obtained from the same anatomical site at different timepoints. The physicians indicated the presence of crackles in individual recordings and which recording from each couple eventually had more intense crackles. Fleiss' kappa coefficient was used to measure inter- and intra-rater agreement.

Results: Fifty-two patients, mostly with a diagnosis of IPF (n = 40, 76.9%) were prospectively enrolled between October 2019 and May 2021. The final acoustic dataset included 702 single recordings, corresponding to 351 couples of recordings from baseline and 12-months timepoints. Kappa coefficient was 0.57 (95% CI 0.55-0.58) for the presence of crackles and 0.42 (95% CI 0.41-0.43) for acoustic change. Intra-rater agreement, measured for three respiratory physicians on three repeated assessments, ranged from good to excellent for the presence of crackles (κ = 0.87, κ = 0.86, κ = 0.79), and from moderate to good for acoustic change (κ = 0.75, κ = 0.76, κ = 0.57).

Conclusions: Agreement between respiratory physicians for the presence of crackles and acoustic change was acceptable, suggesting that crackles represent a reliable acoustic finding in patients with fibrotic ILD. Their role as a lung-derived indicator of disease progression merits further studies.

Keywords: Crackles; Interstitial lung disease; Lung sounds; Pulmonary fibrosis.

Fig. 1

Flow-chart of how lung sounds were assessed. Each electronic folder per patient contained two anonymized recordings obtained from the same recording site (right lower region, in the example shown in the figure) at baseline and 12 months. The two recordings were played consecutively. Each physician was asked to indicate whether crackles were absent or present in each recording. If crackles were indicated as present in both recordings, the physician was asked to indicate which recording had the more intense crackles, or if there was no difference in crackles’ intensity between the two recordings

Fig. 2

Flowchart of data collection

Fig. 3

Crackles in single recordings (panel A) and acoustic change events (panel B) reported by respiratory physicians. Data are mean percentages among all nine physicians

Fig. 4

Kaplan-Meyer curves for progression-free survival of patients with or without significant acoustic progression (APS ≥ 16 and APS < 16, respectively) between baseline and 12 months. Progression-free survival was defined as decline in absolute % predicted FVC ≥ 10% from baseline or death from any cause