The results of lung function studies in 21 healthy young subjects and 12 patients with obstructive ventilatory disturbances are presented. In this study a new method is applied, in which, after a sudden change of the inspiratory concentration of three gases with different diffusing properties (Ar, O2, and CO2), the alveolar washin processes are continuouslty recorded. It is shown, hat inboth, the healthy persons and the patients, two functional lung compartments can be found. In the healthy subjects we find on the average a hypoventilation (VA=1.23 1/min), a relatively high perfusion (Q = 2.25 l/min), and a corresponding high O2 diffusing capacity (DL=16 ml/min · mm Hg) in the smaller compartment (38 % of the alveolar volume). The larger compartment (62% of the alveolar volume) is hyperventilated (VA=4.35 l/min), is relatively lesser perfused (Q = 2.80 l/min), and shows a minimally smaller O2 diffusing capacity (DL=15 ml/min · mm Hg). In the patients with obstructive ventilatory disturbances, however, the hypoventilated compartment (VA=1.77 l/min, Q=4.20 l/min) has a mean alveolar volume of 60% and contributes the major part to the O2 diffusing capacity (DL=14 ml/min mm Hg). The relatively hyperventilated compartment (VA=3.50 l/min, Q = 1.89 1/min) with an alveolar volume of 40% has only a diffusing capacity of DL=4 ml/min mm Hg. From these inhomogeneities of the functional values, 3 portions of the alveolar-arterial O2 pressure difference AaDo2 can be calculated: (1) the part caused by the distribution of Va/Q (AaDDistr 1); (2) the part influenced by the distribution of Dl/Q (AaDDistr·2), and (3) the part produced by arteriovenous shunts (AaDsh). On the average we find for the group of the healthy subjects: AaDDistr. 1 = 8.6 mm Hg, AaDDistr. 2 = 0.3 mm Hg, and AaDSh = 5.9 mm Hg. In the patients, all three portions are considerably larger: AaDDistr. 1 = 16.9 mm Hg, AaDDistr. 2 = 7.0 mm Hg, and AaDSh = 10.5 mm Hg.

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