Purpose: We investigated whether spectral analysis with fast Fourier transform (FFT) of inspiratory lung sounds is useful in the diagnosis and evaluation of the severity of interstitial pneumonia (IP).
Subjects and methods: The study population included 10 healthy volunteers (healthy group) and 21 patients with IP (IP group). We generated inspiratory averaged linear intensities using FFT and determined frequency at maximum sound intensity (Fmax), and quartile frequencies (f25, f50, and f75), compared these values between the groups, generated receiver operating characteristic curves to compare the detectability of IP between the indices and auscultation in all cases, and tested for the correlation of these indices with pulmonary function tests and the fibrosis scores from high-resolution computed tomography images assessed by 3 observers.
Results: Both f50 and f75 were significantly higher in the IP group, but their ability to detect IP was inferior to that of auscultation. They had negative correlations with percent vital capacity and had positive correlations with the fibrosis scores calculated by the 3 different observers.
Discussion: These results were considered to reflect the presence of fine crackles and alterations in pulmonary sound-conduction characteristics caused by IP and indicate that spectral analysis of lung sounds is useful in the diagnosis and evaluation of the severity of IP, although future study is necessary to improve its utility.