Abnormalitis in the distributions of ventilation-perfusion ratios and diffusing capacity-perfusion ratios in three types of chronic obstructive pulmonary disease

To assess whether diffusion-limited gas exchange plays a significant role in hypoxemia in various types of chronic obstructive pulmonary disease (COPD), we analyzed the distribution of ventilation-perfusion (V̇(Λ)/Q̇) ratios and of diffusing capacity-perfusion (G/Q̇) raiots. We compared V̇(Λ)/Q̇ and G/Q̇ distributions in patients with three basic types of COPD; emphysematous changes, bronchiolar involvement, and airway hypersecretion, which were classified based on symptoms and on findings of high resolution CT. The results were that 1) hypoxemia was not caused by diffusion-limited gas exchange with low G/Q̇ regions in any type of COPD, that 2) hypoxemia in COPD was caused by inhomogeneities in V̇(Λ)/Q̇ distribution, that 3) emphysematous changes and bronchial involvement were associated with high and low V̇(Λ)/Q̇ regions, respectively, and that 4) either hypersecretion itself or related airway abnormalities may cause low V̇(Λ)/Q̇ regions to form.