Computed Tomography–Derived Nakata Index as a Predictor of Functional Impairment in Chronic Obstructive Pulmonary Disease

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PURPOSE: Pulmonary vascular remodeling is a key factor in chronic obstructive pulmonary disease (COPD) progression, but noninvasive prognostic markers are limited. This study assessed whether the computed tomography (CT)-derived Nakata index, a measure of body surface area-adjusted pulmonary arterial cross-sectional area, predicts functional impairment in COPD patients. MATERIALS AND METHODS: This retrospective cohort study included 82 COPD patients who underwent thoracic CT and six-minute walk testing (6MWT) from 2023 to 2025. Patients were divided into severely impaired (<334 m, n=18) and less impaired (≥334 m, n=64) groups based on 6MWT distance. Nakata index, pulmonary artery diameters, McGoon ratio, and echocardiographic parameters were evaluated. Multivariate logistic regression identified predictors of severe functional impairment, and receiver operating characteristic (ROC) analysis determined optimal thresholds. RESULTS: Severely impaired patients had a higher Nakata index (395 vs. 330 mm2/m2, P<0.001) and larger left (21.5 vs. 19 mm, P=0.002) and right (22.2 vs. 20 mm, P=0.004) pulmonary artery diameters. Multivariate analysis identified elevated Nakata index (odds ratio: 1.0110, P=0.036), increased left pulmonary artery diameter (odds ratio: 1.3683, P=0.038), and enlarged left atrial diameter (odds ratio: 1.1075, P=0.015) as independent predictors of severe impairment. A Nakata index >373 mm2/m2 showed optimal discriminatory performance (area under the curve: 0.791, sensitivity: 75%, and specificity: 72%). CONCLUSIONS: CT-derived Nakata index is independently associated with severe functional impairment in chronic obstructive pulmonary disease, offering superior discriminatory value over simple diameter measurements. This marker may enhance risk stratification and guide treatment strategies.

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