FIGURE 5.

Diffusion capacity of the lung for oxygen (D_LO2) strongly depends on perfusion and ventilation. (A) Illustration of capillary recruitment (left) and alveolar expansion (right). (B) Diffusion capacity of the lung for oxygen (D_LO2) depending on capillary recruitment and alveolar expansion for a parallel (left) and antiparallel combination (right). Alveolar expansion and the ensuing surface exposure are simulated in Alvin by increasing alveolar surface area from 0 (0%) to 207,000 μm² (100%) in steps of 12.5%. Capillary recruitment is represented by capillary blood volume increase from 0 (0%) to 808,000 μm³ (100%) in steps of 12.5% in Alvin. (C) Comparison to published D_LO2 estimates (Kulish, 2006) (black). Pulmonary blood flow was interpreted as blood volume in Alvin, assuming a flow velocity of 1.5 mm/s and morphological features (mean capillary length of 500 μm (Weibel et al., 1993) and maximum volume of alveolar capillary bed 808,000 μm³ (Gehr et al., 1978; Ochs et al., 2004)). Alveolar surface exposure was fixed at constant values (blue dashed lines) and adjusted with increasing pulmonary blood flow (red line).