[Distribution of inspired and alveolar gases in the lung]

Alveolar components in single breath tests were studied in normal subjects and patients with COPD using simultaneous He and N2 single breath washout and the "Air N2 method" developed in our laboratory since 1979, which was summarized as follows: Special device for the N2 fractional output of a mass spectrometer (Perkin Elmer MGA1100B) was made using a DC cancellation amplifier with inspired N2 concentration (FIN2) suppressed to zero voltage and the changing fraction (FEN2-FIN2) of expired N2 concentration (FEN2) was magnified by the high fidelity DC amplifier. FAirN2 (=FEN2-FIN2) versus expired volume (VE) was designated "Air N2 Curve" with prominent cardiac oscillations (CO) on its mild ascending plateau in normal subjects. Air N2 curve of COPD, however, showed a much steeper ascending plateau without CO. The slope of the air N2 curve under normal resting tidal volume breathing, expressed as the increase in nitrogen concentration per liter BTPS expired (delta AirN2), has been of particular value in the diagnosis of COPD as a new indicator of V A/Q inequality. The air N2 curve expired from tidal volume breath to residual volume (RV) was utilized to analyze phase IV and V. Fractional concentration of Air N2 ceased to increase with the appearance of phase IV and thereafter began to decrease, and then showed abrupt terminal rise at the onset of phase V. High VA/Q units must contribute to phase IV and to the contrary low VA/Q units must contribute to phase V. This provided supporting evidence of the contribution of upper lung regions in causing phase IV and of lower lung regions in causing phase V. Combined He bolus and N2 washout and Air N2 methods with changing expiratory flow rates proved phase IV and V to be flow-dependent. Closing volume (CV) in a static condition could be determined by the extrapolation of phase IV volume to zero flow. Phase IV and V were also shown to be parallel compartments of gravity dependence by the technique of postural change between inspiration and expiration. Simultaneous He and N2 washout curves revealed terminal falling He against continuous rising N2 without CO in COPD. This dissociation of slopes of alveolar plateaus was never seen in normal subjects when the usual amount of He bolus (200 ml) was introduced properly on RV. This offers the possibility of a unique, physiologically significant method to diagnose COPD indicating the disappearance of interregional non-homogeneity and the development of much more serious intraregional non-homogeneity with increased residual volume of poorly ventilated units.