Reproducibility of the vesicular breath sounds in normal subjects

Nonfiltered (NF) lung sounds from the apical area of the heart along with lung volumes and ECG signals were recorded from 5 normal subjects. The signals were digitized and subjected to three methods of heart sound cancellation: 75-Hz high-pass filtering (75 HF), ECG-triggered blanking (BL) and adaptive noise cancelling (AF) [IEEE Trans. Biomed. Engng 33: 1141-1148, 1986]. The sound signals were then subjected to the fast Fourier transform algorithm to obtain power spectra. Five breaths from each subject were analyzed, and their spectra were similar and slightly skewed to the right. The average values of mean, median and mode frequencies of the whole breath of 5 subjects, respectively, were for NF: 64.62 +/- 3.74, 44.57 +/- 2.06 and 36.75 +/- 1.79 Hz; for 75 HF: 150.42 +/- 17.49, 114.02 +/- 6.43 and 86.16 +/- 3.13 Hz; for BL: 81.76 +/- 6.02, 52.36 +/- 2.79, 41.10 +/- 3.15 Hz; for AF: 96.87 +/- 11.58, 68.23 +/- 10.44 and 52.25 +/- 8.97 Hz. These values showed no differences between subjects. The F values obtained by the two-way analysis of variance of all breaths of all subjects (mean, median, mode) were: NF: 0.161, 0.341, 0.089; 75 HF: 0.455, 0.042, 0.085; BL: 0.108, 0.082, 0.057; AF: 0.130, 0.204, 0.113 (all p greater than 0.1). The data revealed a remarkable lack of variation within and between subjects, suggesting similar sites and mechanisms of production and transmission.