Factors affecting a single-breath N2 washout phase IV.

A lung model was constructed to examine the effects of the following factors on the phase IV of a single-breath N2 washout: the lung's elasticity change with age, closing pressure (CP), regional volume (Volr) distribution, pleural pressure, and gradient (Grad). The analysis revealed 1) when the CP was assumed to be + 1.0 cmH2O, predicted changes in closing capacity (CC) due to alterations in elasticity agreed with previous experimental results for individuals above 40 yr; for younger age groups, the predicted values were apparently larger, suggesting the CP may be near zero; 2) difference in Volr distribution alone caused alterations in CC and the slope of phase IV; 3) for 1 cmH2O elevation of CP, closing capacity /total lung capacity (CC/TLC) was predicted to increase about 8%; 4) for 0.1 cmHiO/cm Grad increase, CC/TLC was predicted to rise approximately 7%. In conclusion, multiple factors affect phase IV.