Simultaneous helium and nitrogen single-breath washout: lung model simulation.

By use of a model, simultaneous bolus and resident N2-washout curves are simulated to examine the effects of inhomogeneous lung elasticity and unequal critical airway closing pressure. Pathological conditions are divided into A, B, and C, where dominant lesions involve the upper, entire vertical, and lower regions, respectively. In elastic inhomogeneity, the He plateau (phase III) is upward, flat, or downward in conditions A, B, and C, respectively, depending on the vertical location of the lesion. Conversely, the N2 plateau is upward in three conditions, reflecting overall interregional and intraregional inhomogeneity. The terminal He rise (phase IV) has a clear relationship to the airway closure than the terminal N2 rise. The present study supports the previous prediction that the simultaneous bolus and N2-washout study provides additional information. This analysis will improve the means for assessing mechanical disorders in diseased lungs.