The relation between physical activity and cardiac autonomic dysfunction in patients with chronic obstructive pulmonary disease

BACKGROUND: Cardiac autonomic dysfunction is common in patients with chronic obstructive pulmonary disease (COPD). Although exercise training improves cardiac autonomic function, the effects of changing physical activity on cardiac autonomic function remain unknown. OBJECTIVE: This study aimed to (1) investigate the association between cardiac autonomic function, exercise capacity and physical activity cross-sectionally and (2) relate changes in physical activity, as a result of a 6-month coaching program, to changes in cardiac autonomic function. METHODS: Autonomic function was assessed objectively using the Polar H10 sensor, measuring (1) resting heart rate during sleep; (2) heart rate variability (SDNN, RMSSD, LF/HF ratio and SD2/SD1 ratio) during sleep and (3) heart rate recovery following the 6-minute walking test (6MWT), and subjectively using the COMPASS 31 questionnaire at baseline and 6-months follow-up. Physical activity (steps per day and movement intensity during walking) was measured using accelerometery. Cross-sectional and longitudinal associations were evaluated. RESULTS: In 36 patients with COPD (69% male, mean ± SD age 69 ± 7 years, FEV1 53 ± 13%pred, 28% taking β-blockers), baseline cross-sectional analyses showed weak to moderate associations between heart rate recovery and movement intensity during walking (rs = 0.45) and distance covered during 6MWT (rs = 0.55). Longitudinal analyses over 6-months follow-up showed that changes in daily step count were inversely associated with changes in resting heart rate (rs = -0.48), LF/HF ratio (rs = -0.35) and SD2/SD1 ratio (rs = -0.28) and that changes in movement intensity during walking were inversely associated with changes in SD2/SD1 ratio (rs = -0.51) in patients not taking β-blockers. CONCLUSION: Weak cross-sectional associations were observed between certain parameters of cardiac autonomic function, exercise capacity and physical activity. Increasing the amount of physical activity showed a weak relation with lowering resting heart rate over 6 months in patients not taking influencing medication.