Objective: Patients with interstitial pulmonary fibrosis (IPF) often have diffusely abnormal findings on chest radiographs, making it difficult to detect evidence of superimposed congestive heart failure (CHF) or pneumonia. The goal of this study was to determine whether the crackles of IPF differed in their transmission and frequency from crackles of CHF and pneumonia in the hope of improving diagnosis and monitoring of these patients.
Methods: A multichannel lung sound analyzer was used to collect 20-s samples of sound from 25 patients with pneumonia, 17 patients with CHF, and 19 patients with IPF. We calculated a crackle transmission coefficient (CTC) by quantifying the distance a crackle spreads using a technique that cross-correlated the signal containing the highest amplitude crackle with the corresponding signal on all other ipsilateral channels: CTC, 0% = no transmission; CTC, 100% = equal transmission to all channels.
Results: Both the CTC and the crackle frequency in IPF were statistically different from that in CHF and pneumonia (p < 0.0001). The CTC averaged 24 ± 5% for pneumonia, 25 ± 8% for CHF, and 14 ± 4% for IPF. The crackle frequency averaged 302 ± 47 Hz for pneumonia, 311 ± 62 Hz for CHF, and 462 ± 50 Hz for IPF (± SD).
Conclusion: These differences in CTC and crackle frequency offer the promise of helping guide treatment in IPF patients.