[Phases of the nitrogen washout curve with different gas mixtures in the lungs]

The phases of the nitrogen washout curve (NWC): dead space phase (DSP), mixed phase (MP), alveolar phase (AP) and lung closing volume (LCV) were studied in 7 healthy subjects and 47 patients with diverse disorders of gas mixing in the lungs. Under conditions of a diffuse decrease in the elasticity induced by blood congestion consequent on mitral heart disease, the gas in uniformly mixed in the lungs so that the magnitudes of NWC phases (in % of ZCV) almost do not differ from normal. When ZCV was drastically decreased, DSP showed a relative augmentation, while AP fell down. In local ventilation disorders induced by pulmonary diseases (bronchoectasis, abscesses, etc.), NWC patterns demonstrated significant changes indicating a non-uniform gas mixing in the lungs. LCV was well identifiable in healthy subjects whereas in patients with heart diseases, it was more poorly and less frequently identifiable, especially in subjects with pulmonary diseases. An increase in the time of diffuse gas mixing, which was attained as a result of breath holding at the height of inspiration, leads to the reduced DSP magnitude and gas supply to the alveoli. This does not improve, however, gas exchange in the most poorly ventilated zones.