Factors affecting a single-breath N2 washout phase IV

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Abstract
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). When the CP was assumed to be +1.0 cm H2O, 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. Difference in Volr distribution alone caused alterations in CC and the slope of phase IV. For 1 cmH2O elevation of CP, closing capacity/total lung capacity (CC/TLC) was predicted to increase about 8% and for 0.1 cmH2O/cm Grad increase, CC/TLC was predicted to rise approximately 7%. Multiple factors apparently affect phase IV.