Collapsibility of Lung Volume by Paired Inspiratiory and Expiratory CT Scans: Correlations with Lung Function and Mean Lung Density

Abstract

Rationale and Objectives: To evaluate the relationship between measurements of lung volume (LV) on inspiratory/expiratory computed tomography (CT) scans, pulmonary function tests (PFT), and CT measurements of emphysema in individuals with chronic obstructive pulmonary disease.

Materials and Methods: Forty-six smokers (20 females and 26 males; age range 46-81 years), enrolled in the Lung Tissue Research Consortium, underwent PFT and chest CT at full inspiration and expiration. Inspiratory and expiratory LV values were automatically measured by open-source software, and the expiratory/inspiratory (E/I) ratio of LV was calculated. Mean lung density (MILD) and low attenuation area percent (<-950 HU) were also measured. Correlations of LV measurements with lung function and other CT indices were evaluated by the Spearman rank correlation test.

Results: LV E/I ratio significantly correlated with the following: the percentage of predicted value of forced expiratory volume in the first second (FEV1), the ratio of FEV1 to forced vital capacity (FVC), and the ratio of residual volume (RV) to total lung capacity (TLC) (FEV1 %P, R = -0.56, P < .0001; FEV1/FVC, r = -0.59, P <.0001; RV/TLC, r = 0.57, P <.0001, respectively). A higher correlation coefficient was observed between expiratory LV and expiratory MILD (r = -0.73, P <.0001) than between inspiratory LV and inspiratory MILD (r = -0.46, P < .01). LV E/I ratio showed a very strong correlation to MILD E/I ratio (r = 0.95, P <.0001).

Conclusions: LV E/I ratio can be considered to be equivalent to MLD E/I ratio and to reflect airflow limitation and air-trapping. Higher collapsibility of lung volume, observed by inspiratory/expiratory CT, indicates less severe conditions in chronic obstructive pulmonary disease.