VENTILATION INHOMOGENEITIES AND MIXED VENOUS-BLOOD N-2 IN MULTIBREATHN-2 WASHOUT

The single path model of airway gas transport, with and without a dist ributed blood source term, was used to simulate multiple-breath N-2 wa shout by breathing pure O-2 in two lung models: a single-region lung m odel (SRLM) which produces series inhomogeneity, and a seven-region lu ng model (7RLM) incorporating both series and parallel inhomogeneities . Normalized phase III slopes (Sn) from N-2 expirograms were computed for each breath and compared with published human experimental data ob tained under similar conditions. The 7RLM predicts well the trend of e xperimental Sn N-2 changes and is superior to the SRLM in the first pa rt (the unsteady state), implying that this part of the curve is mostl y due to convective mixing of the seven parallel flow streams. In the quasi-steady state, the 7RLM is not obviously superior to the SRLM. Fu nctional residual capacity and pulmonary perfusion are shown to strong ly affect the number of breaths required to reach the quasi-steady sta te. The anatomical dimensions that appear to be critical in SRLM are n ot as important in the 7RLM. (C) 1997 Elsevier Science B.V.