OBJECTIVE. This study evaluates the relationships between quantitative CT (QCT) and spirometric measurements of disease severity in cigarette smokers with and without chronic obstructive pulmonary disease (COPD).

MATERIALS AND METHODS. Inspiratory and expiratory CT scans of 4062 subjects in the Genetic Epidemiology of COPD (COPDGene) Study were evaluated. Measures examined included emphysema, defined as the percentage of low-attenuation areas ≤ –950 HU on inspiratory CT, which we refer to as “LAA-950_I”; air trapping, defined as the percentage of low-attenuation areas ≤ –856 HU on expiratory CT, which we refer to as “LAA-856_E”; and the inner diameter, inner and outer areas, wall area, airway wall thickness, and square root of the wall area of a hypothetical airway of 10-mm internal perimeter of segmental and subsegmental airways. Correlations were determined between spirometry and several QCT measures using statistics software (SAS, version 9.2).

RESULTS. QCT measurements of low-attenuation areas correlate strongly and significantly (p < 0.0001) with spirometry. The correlation between LAA-856_E and forced expiratory volume in 1 second (FEV₁) and the ratio of FEV₁ to forced vital capacity (FVC) (r = –0.77 and –0.84, respectively) is stronger than the correlation between LAA-950_I and FEV₁ and FEV₁/FVC (r = –0.67 and r = –0.76). Inspiratory and expiratory volume changes decreased with increasing disease severity, as measured by the Global Initiative for Chronic Obstructive Pulmonary Disease (GOLD) staging system (p < 0.0001). When airway variables were included with low-attenuation area measures in a multiple regression model, the model accounted for a statistically greater proportion of variation in FEV₁ and FEV₁/FVC (R² = 0.72 and 0.77, respectively). Airway measurements alone are less correlated with spirometric measures of FEV₁ (r = 0.15 to –0.44) and FEV₁/FVC (r = 0.19 to –0.34).

CONCLUSION. QCT measurements are strongly associated with spirometric results showing impairment in smokers. LAA-856_E strongly correlates with physiologic measurements of airway obstruction. Airway measurements can be used concurrently with QCT measures of low-attenuation areas to accurately predict lung function.