Interactional effects of depressive symptoms and physical function on daily physical activity in ambulatory patients receiving hemodialysis

Abstract

Background: Clarification of the factors associated with decreased physical activity is crucial for effective disease management in patients undergoing hemodialysis. Although evidence suggests that physical activity may be associated with physical function or depressive symptoms, limited studies have demonstrated these factors to be independently associated with the former in patients undergoing hemodialysis. This study aimed to examine whether physical function and depressive symptoms were independently or interactively associated with daily physical activity in patients undergoing hemodialysis. Methods: This cross-sectional study analyzed 157 clinically stable outpatients (median age: 68 years) receiving hemodialysis. Physical activity (steps/day) was measured using an accelerometer for four consecutive non-dialysis days. Physical function was evaluated by calculating usual walking speed along a 10-m walkway. The 10-item version of the Center for Epidemiologic Studies for Depression Scale was used to assess depressive symptoms. Results: The hierarchical multiple regression model (Model 2), constructed by adding physical function to Model 1 (clinical characteristics), showed a significant increase in coefficient of determination (R 2), compared to Model 1 (ΔR 2 = 0.15, P < 0.01). There was no significant increase in R 2 between Models 2 and 3, where depressive symptoms were added to Model 2. The interaction term of physical function with depressive symptoms in Model 4 indicated an increase in R 2 (ΔR 2 = 0.01, P = 0.03), compared with Model 3. The simple slope analysis demonstrated that the difference in physical activity between patients with or without depressive symptoms at higher levels of physical function was greater than that at its lower levels. Conclusions: Physical function was a strong and independent factor associated with physical activity, but no independent relationship between depressive symptoms and the physical activity was observed in patients undergoing hemodialysis. In contrast, physical function and depressive symptoms were interactively associated with daily physical activity in patients undergoing hemodialysis who were capable of walking independently. Our findings suggested that a two-step screening, primarily based on physical function and then depressive symptoms, can be useful to identify factors associated with physical inactivity in hemodialysis patients.