[Calculations of airway parameters from expiratory concentration volume values based on the model of stationary bronchoalveolar gas exchange (author's transl)].
Approximating the cumulative cross section of the terminal airway structure by a single parabolic exponential term with the unknown parameters initial cross section a, exponential steepness b and external dead space VDE, calculations of the stationary concentration front F along airway length L, raising during constant flow inspiration, were done, solving the gas transport equation for stationary conditions numerically and integrating the distribution of dF/dL. The conversion to the expiratory F-V profile was done neglecting pulmonary inhomogeneity and expiratory front deformation. Calculations were applied on a scale of different a and b enclosing normal and some pathological lung models. Applying different inspiratory flows, there is a linear correlation between the reciprocal steepness dV/dF of expiratory F-V diagrams and the flow diffusion ratio V/D*, where D* is the effective diffusivity of gases. Compared to normal, the model of nonobstructive emphysema shows higher values of dV/dF and the general obstruction lower ones; all three have the same increase of dV/dF along V/D*. The peripheral obstruction type has the highest slope of regression along V/D* and the obstructive emphysema the lowest one. Mathematical approximations of the regression between dV/dF of the expiratory F-V diagram at certain intervals of F and V/D* were used to present a procedure calculating airway parameters a, b, VDE and the effective diffusivity D* from a sequence of F-V diagrams applying different inspiratory flows.
D000402:Airway Obstruction / Q000503:physiopathology; D004646:Emphysema / Q000503:physiopathology; D006801:Humans; D008176:Lung Volume Measurements / Q000379:methods*; D008433:Mathematics; D008954:Models, Biological; D010101:Oxygen Consumption
Berechnung der Atemwegsparameter aus exspiratorischen Konzentrations-Volumen-Daten auf der Basis stationärer bronchoalveolärer Gaswechselbedingungen.