Am. J. Respir. Crit. Care Med., Volume 156, Number 1, July 1997, 86-93

Inhomogeneities of Ventilation and the Diffusing Capacity to Perfusion in Various Chronic Lung Diseases

KAZUHIRO YAMAGUCHI, MASAAKI MORI, AKIRA KAWAI, TOMOAKI TAKASUGI, YOSHITAKA OYAMADA, and EIICHI KODA

Departments of Medicine and Radiology, School of Medicine, Keio University, Tokyo, Japan

Although impairment of gas exchange caused by ventilation-perfusion ( A/) mismatch has been extensively analyzed, there have been no systematic studies focused on determining the distributions of diffusion properties in close connection with those of A/. We attempted to clarify the simultaneous distributions of A/ and diffusion capacity to perfusion (D/) in patients with idiopathic pulmonary fibrosis (IPF) or chronic obstructive pulmonary disease (COPD). To assess pathologic determinants causing functional abnormalities, we compared A/ and D/ distributions with the findings on high-resolution computed tomography. O ₂, CO₂, and CO together with six foreign inert gases were used as indicator gases. We transformed the measured data on indicator gases in arterial blood into a continuous distribution of in the A/-D/ field. In IPF, active alveolitis or acinitis played a major role in producing low D/ regions impeding gas exchange via a diffusion limitation, whereas extensive fibrosis with minimal inflammation accounted for low D/ as well as low A/ regions. In COPD, no regions with low D/ ratios were observed, but an abnormality in the A/ distribution with low or high A/ ratios was identified. Emphysematous lesions produced high A/ regions, whereas peripheral airway involvement yielded low A/ regions. These findings suggest that hypoxemia in patients with IPF is caused by inhomogeneous distributions of D/ in combination with those of A/. Hypoxemia in patients with COPD is attributable primarily to inhomogeneities in A/ rather than in D/ distributions.

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