Prediction of Pulmonary Function in Patients with Chronic Obstructive Pulmonary Disease: Correlation with Quantitative CT Parameters

Abstract

Objective: We aimed to evaluate correlations between computed tomography (CT) parameters and pulmonary function test (PFT) parameters according to disease severity in patients with chronic obstructive pulmonary disease (COPD), and to determine whether CT parameters can be used to predict PFT indices.

Materials and methods: A total of 370 patients with COPD were grouped based on disease severity according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) I-IV criteria. Emphysema index (EI), air-trapping index, and airway parameters such as the square root of wall area of a hypothetical airway with an internal perimeter of 10 mm (Pi10) were measured using automatic segmentation software. Clinical characteristics including PFT results and quantitative CT parameters according to GOLD criteria were compared using ANOVA. The correlations between CT parameters and PFT indices, including the ratio of forced expiratory volume in one second to forced vital capacity (FEV₁/FVC) and FEV₁, were assessed. To evaluate whether CT parameters can be used to predict PFT indices, multiple linear regression analyses were performed for all patients, Group 1 (GOLD I and II), and Group 2 (GOLD III and IV).

Results: Pulmonary function deteriorated with increase in disease severity according to the GOLD criteria (p < 0.001). Parenchymal attenuation parameters were significantly worse in patients with higher GOLD stages (p < 0.001), and Pi10 was highest for patients with GOLD III (4.41 ± 0.94 mm). Airway parameters were nonlinearly correlated with PFT results, and Pi10 demonstrated mild correlation with FEV₁/FVC in patients with GOLD II and III (r = 0.16, p = 0.06 and r = 0.21, p = 0.04, respectively). Parenchymal attenuation parameters, airway parameters, EI, and Pi10 were identified as predictors of FEV₁/FVC for the entire study sample and for Group 1 (R² = 0.38 and 0.22, respectively; p < 0.001). However, only parenchymal attenuation parameter, EI, was identified as a predictor of FEV₁/FVC for Group 2 (R² = 0.37, p < 0.001). Similar results were obtained for FEV₁.

Conclusion: Airway and parenchymal attenuation parameters are independent predictors of pulmonary function in patients with mild COPD, whereas parenchymal attenuation parameters are dominant independent predictors of pulmonary function in patients with severe COPD.

Keywords: Chronic obstructive pulmonary disease; Computed tomography; Emphysema; Pulmonary function test; Quantitative.

Fig. 1. Scatter plots of correlations between EI (A, C) or ATI (B, D) and pulmonary function indices.

Scatter plots of distributions of four GOLD stages are included in Supplementary Figure 1 (in the online-only Data Supplement). ATI = air-trapping index, EI = emphysema index, FEV₁ = percentage predicted forced expiratory volume in one second, FEV₁/FVC = ratio of forced expiratory volume in one second to forced vital capacity, GOLD = Global Initiative for Chronic Obstructive Lung Disease

Fig. 2. Scatter plots of correlations of airway wall thickness (A, C) and WA% (B, D) with pulmonary function indices.

Scatter plots of distributions of four GOLD stages are included in Supplementary Figure 2 (in the online-only Data Supplement). WA% = wall area percentage

Fig. 3. Distribution of CT parameters according to GOLD stages.

(A) Changes in lung volume ([inspiratory volume − expiratory volume] / inspiratory volume × 100) in whole lungs, (B) inspiratory MLD, (C) ATI (ratio of MLD on expiration and inspiration), and (D) EI measured on inspiration CT according to GOLD stages. Change in lung volume is smaller for more advanced GOLD stages. Inspiratory MLD as well as ATI decrease, whereas EI increases, with increase in GOLD stage. CT = computed tomography, HU = Hounsfield unit, MLD = mean lung density