Respiratory Changes in the Superior Vena Cava Area on Inspiratory and Expiratory Chest CT: Comparison between Patients with COPD and with Bronchial Asthma

Purpose: In patients with obstructive lung diseases, alteration of intrathoracic pressure is closely related to hyperinflation and leads to hemodynamic impairments. Both intrathoracic pressure and hemodynamics are affected by the respiratory phase. In fact, a previous study showed that respiratory phasic variations in the superior vena cava (SVC) area significantly correlated with the extent of emphysema. Chronic obstructive pulmonary disease (COPD) and bronchial asthma manifest different pathophysiological changes in hyperinflation and hemodynamics. The current study was conducted to evaluate differences in respiratory variations in the cross-sectional area of the SVC between patients with COPD and with asthma. Materials and Methods: We measured the SVC area and calculated the ratio of the SVC area on inspiratory and expiratory scans (i/e-SVC ratio) in 66 patients with COPD and 16 patients with asthma. The cor-relations of the i/e-SVC ratios with airflow limitation, pulmonary small vessels less than 5 mm2 (%cross-sectional area [%CSA] < 5), and respiratory changes in lung volume (i/e-LV) obtained by inspiratory and expiratory computed tomography (CT) images were evaluated. Results: There was no significant difference in i/e-SVC ratio between COPD and asthma groups. In COPD patients, the i/e-SVC ratio significantly correlated with the %CSA < 5 (ρ = ﹣0.433, P = 0.003), i/e-LV ratio (ρ = ﹣0.371, P = 0.011), and percent of predicted forced expiratory volume in 1 second (FEV1% predicted) (ρ = ﹣0.474, P = 0.001), whereas in asthma patients, there were no significant correlations between the i/e-SVC ratio and those functional parameters. Conclusion: There would be differences in the relationship between intrathoracic pressure and cardiopulmonary hemodynamics between COPD and asthma patients.