The lung sounds phase angle test for detection of small airway disease.

Nineteen normal subjects and fifteen smokers with minimal symptoms were studied. All subjects performed spirograms, maximal expiratory flow volume (MEFV) maneuvers both breathing air and 80% He and 20% O2 mixture, pressure-volume maneuvers, and single breath N2 washout curves with preceding thoracic gas volume, from which closing capacity (CC), closing volume (CV), and slope of phase III (delta N2) were computed. Pulmonary resistances (RL) and compliances (CL) at various breathing frequencies were also measured. The sequence of breath sounds during the inspiratory phase of tidal breathing as assessed by lung sounds (lung sounds ventilation sequence indices (theta) was measured between two positions from various parts of the right lung in the same horizontal level. None of the normal subjects had a mean theta larger than 5 degrees. Eleven out of 15 smokers had a mean theta greater than 5 degrees. The mean theta correlated significantly with CLdyn/CLst, but not with CC, CV, delta Vmax50, delta N2 and FEF25-75. It is concluded that theta is an index of intraregional inhomogeneity of time constants.