Aim: It has been reported that patients with chronic obstructive pulmonary disease (COPD) exhibit impaired autonomic control as assessed by heart rate variability (HRV) analysis. However, it is unknown whether dynamic markers from the heart rate may identify autonomic dysfunction linked with disease severity and respiratory function. This study evaluated the cardiac autonomic responses after completing a conventional walk challenge in these patients.
Methods: The study included forty-six COPD patients who performed a standard six-minute walk test (6MWT). An ECG signal (lead II) was acquired before, during, and after the test using a wearable device attached to the patient’s chest. Inter-beat interval time-series (RR intervals) were evaluated and used to assess the heart rate (HR) dynamic during recovery. The HR dynamic was compared among patient groups classified according to standard metrics of disease severity, i.e. GOLD classification.
Results: The heart rate recovery (HRR) marker, evaluated at standard timings (at first and second minute) but also every 5 s throughout recovery following the 6MWT showed different dynamic trends among subgroups. Significantly larger HRR values (normalized by the maximum HR after the walking period) were found in less severe COPD patients (n=23, GOLD={1,2}; HRR1=14.8±7.5%, HRR2=18.6±8.1%) compared to those with more disease severity (n=23, GOLD={3,4}; HRR1=9.3±5.8%, p=0.002; and HRR2= 13.7±6.7%, p=0.041). The largest differences among groups were observed around the first 30 s of the recovery phase (HRR=10.8±6.6% vs HRR=5.6±4% p=0.001).
Conclusions: Disease severity in COPD patients appears to be associated with dysfunctional autonomic control, as assessed by heart rate dynamic profiles when recovering from a walking challenge. Our results showed a slower recovery for patients who had worse diagnoses, probably due to a weaker response of vagal control reactivation. This suggests that, besides respiratory markers, cardiac parameters may provide valuable information for a better characterization of disease severity in COPD patients.