Airflow limitation in chronic obstructive pulmonary disease. Ratio and difference of percentage of low-attenuation lung regions in paired inspiratory/expiratory computed tomography

Rationale and Objectives: The purpose of this study was to analyze the relationship between airflow limitation and two types of computed tomography (CT) measurements: expiratory/inspiratory (E/. I) ratio and E/. I difference of percentage of low-attenuation lung regions (LAA%). Materials and Methods: Thirty patients who underwent inspiratory and expiratory CT scans were included in this study. The CT data were used to calculate the LAA% E/I ratio and E/I difference. Other types of CT measurements were also obtained, including the E/I ratio and E/I difference of lung volume, mean lung density, standard deviation, skewness, and kurtosis. LAA% was calculated at 20 thresholds (-990 to -800HU). Pearson's correlation between the measurements and forced expiratory flow in 1second was used to determine the efficacy of LAA% E/I ratio and E/I difference. P values of <5.88×10^-5 were considered statistically significant with Bonferroni correction. Results: The LAA% E/I ratio and E/I difference significantly correlated with forced expiratory flow in 1second. The best correlation coefficient for the LAA% E/I ratio was -0.699 (P=1.75×10^-5) and for the LAA% E/I difference was -0.723 (P=6.53×10^-6). The best correlation coefficient for the LAA% E/I difference was stronger than that for the other types of CT measurements. Conclusions: The LAA% E/. I ratio and E/. I difference significantly correlated with airflow limitation in chronic obstructive pulmonary disease.