• Naoya Tanabe, Chin Kook Rhee, Susumu Sato, Shigeo Muro, Hiroshi Shima, Kazuya Tanimura, Ki-Suck Jung, Kwang Ha Yoo, and Toyohiro Hirai.
• Department of Respiratory Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
• COPD. 2020 Dec 1; 17 (6): 627-634.

AbstractForced expiratory volume in 1 s (FEV1) is a standard physiological index of chronic obstructive pulmonary disease (COPD), but reflects emphysema and vascular abnormalities less sensitively than diffusion capacity for carbon monoxide (DLCO). This study tested whether a disproportionally impaired DLCO relative to FEV1 (FEV1 z-score>-3 and DLCO z-score≤-3) is a common functional COPD phenotype associated with distinct clinical and structural features and the prognosis of two cohorts. The cross-sectional analyses of the Korea COPD Subgroup Study (KOCOSS) cohort (multicenter study in Korea) included 743 males with COPD whose DLCO was available. The cross-sectional and longitudinal analyses of the Kyoto University Cohort (single-center study in Japan) included 195 males with COPD who were prospectively followed for 10 years. A disproportionally impaired DLCO relative to FEV1 was observed in 29% and 31% of patients in the KOCOSS and Kyoto University cohorts, respectively. In the multivariable analysis, the disproportionally impaired DLCO was associated with worse symptoms, shorter 6-minute walking distance, paraseptal and centrilobular emphysema on computed tomography, and reduced arterial oxygen and carbon dioxide pressures compared to the reference (FEV1 z-score>-3 and DLCO z-score>-3). In the multivariable Cox proportional hazard model, a higher long-term mortality was observed in the disproportionally impaired DLCO group than in the reference group (hazard ratio [95% confidence interval] = 3.09 [1.52-6.29]) and similar to the DLCO z-score≤-3 and FEV1 z-score≤-3 group. The disproportionally impaired DLCO relative to FEV1 is common and associated with increased symptoms, emphysema, arterial blood gas abnormalities, and increased long-term mortality in patients with COPD.

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