摘要：

In 8 standing men we studied the single breath washout of inhaled helium boluses. The volume at which boluses were inhaled (V B) varied from 0% to 8% VC and subjects achieved V B both by expiring from TLC and inspiring from RV. In 3 subjects we also measured the regional distributions of inhaled Xe boluses as V B varied. The slope of Phase III of the alveolar plateau decreased as V B increased in approximately linear fashion, equalling zero at a mean V B of 43% VC. The height of Phase IV declined sharply at low V B, reaching zero at a mean V B of 30% VC. At higher V B Phase IV height declined significantly in four of the eight subjects. Both Phase III slope and Phase IV height correlated strongly with regional pre-expiratory Xe concentrations, but these results also suggested that regional concentration differences were more important determinants of Phase IV than of Phase III. Phase III slope, Phase IV height and closing volume were all the same whether V B was achieved by inspiring or expiring. Bonus distribution, which at high V B was compliance determined, and determined at low V B by airway closure, was independeent of volume history. Closing volume was greater when V B= 10–20%VC than when V B= 0%VC, suggesting that some airways were closed at volumes greater than the conventionally measured closing volume.

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