Heart Rate Recovery After 6-min Walking Test Predicts Acute Exacerbation in COPD

Abnormalities of autonomic function have been reported in patients with chronic obstructive pulmonary disease (COPD). Our objectives were to identify determinants of abnormal heart rate recovery at 1 min (HRR₁) following completion of the 6-min walk test (6MWT) in COPD and to establish whether abnormal HRR₁ predicts acute exacerbations (AECOPD).

Hundred one COPD patients (FEV₁ (SD) 53 (19)  % predicted) were prospectively recruited in a multi-center study. HRR₁ after the 6MWT was evaluated as the difference between heart rate at the end of the test and 1 min into the recovery (HRR₁). Linear and logistic regression was used to identify predictors of HRR₁ and AECOPD, respectively. The best HRR₁ cut-off point to predict AECOPD was selected using the receiver operating characteristics (ROC) curves. The follow-up period was 12 months.

Distance covered during the 6MWT (m) and DLco (% predicted) were independently associated with HRR₁ (r ² = 0.51, p = 0.001). Among several potential covariates, HRR₁ emerged as the most significant predictor of AECOPD (Odds ratio [OR], 0.91 per beat of recovery; 95% confidence interval [CI], 0.85-0.97; p = 0.02). The ROC analysis indicated that subjects with HRR₁ less than 14 beats (AUC, 0.71 [CI] 0.60-0.80; p = 0.0001) were more likely to suffer an exacerbation during the follow-up period (for HRR₁, p = 0.004 [log-rank test]).

HRR₁ after the 6MWT is an independent predictor factor for AECOPD. Further studies are warranted to examine the physiological mechanisms associating a delayed HRR and acute exacerbations in COPD patients.