Interaction of Depressive and Anxiety Symptoms on the Mortality of Patients with COPD: A Preliminary Study

Background: Depressive and anxiety symptoms increase the risk of death in patients with Chronic Obstructive Pulmonary Disease (COPD), but the combined effects of the two factors are unknown. Purpose: To assess the possible interactive effects of depressive and anxiety symptoms on the death of patients with COPD. Methods: Prospective data for 7787 Chinese patients with COPD was analyzed and the deaths were recorded. Depressive and anxiety symptoms were evaluated using the Hospital Anxiety and Depression Scale. A product of depressive and anxiety symptoms was added to the logistic regression model to evaluate the multiplicative interaction, and relative excess risk of interaction (RERI), attributable proportion (AP) of interaction, and synergy index (S) were applied to evaluate the additive interaction of the two factors. Bootstrap was used to calculate 95% confidence intervals (CIs) of RERI, AP and S. RERI > 0, AP > 0, or S > 1 indicated biological interaction. Results: After 4 years' follow-up, the cumulative mortality was 20.0%, and the percentages of deaths in patients with depressive and anxiety symptoms were 28.5% and 30.9%, respectively. When adjusting for variables such as age, sex, disease duration, marital status, income, education level, co-morbidity, smoke status, biomass smoke, 6MWD, MRC, BMI and FEV1. the RERI, AP, and S (with 95% CIs) resulted in depression and anxiety scores of 6.54 (1.23-13.79), 0.54 (0.18-0.83), and 2.64 (1.33-4.75) respectively. Conclusion: Interaction effects were found between depressive and anxiety symptoms on the death of patients with COPD. Patients with both depressive and anxiety symptoms have an increased risk of death from COPD.