The reproducibility of forced expiratory wheezes

Previous work has shown forced expiratory wheezes (FEW) to be associated with onset of flow limitation and to have spectral characteristics similar to wheezes heard in patients with obstructive lung diseases. This study was designed to determine whether the acoustic characteristics of FEW are reproducible under controlled lung volume and flow conditions. Six healthy, nonsmoking young adults 28 to 37 yr of age were studied. They performed FVC maneuvers through a set of round apertures (diameters, 14, 12, 10, 8, 6, 4, 2, and 1 mm). Flow, measured with a pneumotachograph, and tracheal lung sounds, recorded with a Hewlett-Packard HP20510A contact sensor, were recorded simultaneously on magnetic tape and analyzed off-line. For each subject, data from three different aperture sizes, measured in triplicates, were analyzed (total of 54 runs); 199 different wheezes were identified (mean, 3.7 wheezes/run), and 56.7 +/- 5.1% (mean +/- SEM) of wheezes found in a certain run (range, 41.7 to 77.8%) were identical to wheezes found in the other two runs of the same aperture size (i.e., same flow rate). In 17 of the 18 sets of triplicate runs analyzed, at least one major wheeze was identical in all three runs of the set. In three of the sets, two different identical wheezes were found. These findings support a deterministic mechanism of generation of wheezes and is in line with the predictions of the "flutter theory."