Relationship Between Heart Rate Recovery And Disease Severity In Chronic Obstructive Pulmonary Disease Patients

Chronic obstructive pulmonary disease (COPD) patients exhibit impaired autonomic control which can be assessed by heart rate variability analysis. The study aims to evaluate the cardiac autonomic responses of COPD patients after completing a conventional six-minute walk test (6MWT). Fifty COPD patients were included in the study, for which an ECG signal (lead II) was acquired by a wearable device, before, during, and after the test. We used the heart rate (HR) time-series to assess the heart rate dynamic during recovery. The heart rate recovery (HRR) marker was evaluated every 5 s after the 6MWT and showed different dynamic trends among severity groups. We compared the HRR among patient groups classified according to the GOLD standard. Significantly larger normalized HRR values (nHRR) were found in mild COPD patients (n=23, GOLD={1,2}; nHRR(1) =14.8 +/- 7.5 %, nHRR(2)=18.6 +/- 8.1 %) compared to those with more disease severity (n=23, GOLD={3,4}; nHRR(1) =9.3 +/- 5.8 %, p=0.002; and nHRR(2)= 13.7 +/- 6.7 %, p=0.041). The largest differences were observed around the first 30 s of the recovery phase (nHRR=10.8 +/- 6.6 % vs. nHRR=5.6 +/- 4 % p=0.001). Our results showed a slower recovery for the severest patients, suggesting that cardiac parameters like the ones we propose here, may provide valuable information for a better characterization of COPD severity.