Are heart rate dynamics in the transition from rest to submaximal exercise related to maximal cardiorespiratory responses in COPD?

Abstract

Background: Poor exercise capacity is an important negative prognostic marker in patients with chronic obstructive pulmonary disease (COPD). Heart rate variability (HRV) responses can indicate alterations in cardiac autonomic control. Nevertheless, it remains unclear whether these abnormalities are related to cardiorespiratory responses to exercise in these patients.

Objective: To evaluate whether HRV at rest and submaximal exercise are related to impaired cardiopulmonary responses to exercise in COPD patients.

Methods: Fifteen men (66.2±8.7 years) with COPD (FEV₁: 55.1±19.2%) were assessed. The R-R interval (RRi) data collection was performed at rest (stand position) and during the six-minute walk test (6MWT). All patients performed a symptom-limited cardiopulmonary exercise test on a cycle ergometer. The HRV changes from rest to submaximal exercise (Δ rest-6MWT) were calculated.

Results: We found significant correlations between low frequency (LF) and high frequency (HF) Δ rest-6MWT with Δ oxyhemoglobin saturation by pulse oximetry (r=-0.64 and r=0.65, respectively; p<0.05), minute ventilation/carbon dioxide output relationship from beginning to peak exercise (r=-0.52 and r=0.53, p<0.05), and exercise ventilatory power (r=0.52 and r=-0.53, p<0.05). Interestingly, there was a strong positive correlation (r=0.82, p<0.05) between six-minute walk distance (6MWD) and Δ LF/HF from rest to exercise.

Conclusion: HRV analysis in the transition from rest to submaximal exercise is associated with exercise ventilatory and hemodynamic abnormalities in COPD patients. Rehabilitative strategies to improve HRV responses may provide an important tool to clinical practice in these patients.

Keywords: Cardiac autonomic nervous system; Cardiopulmonary exercise testing; Rehabilitation; Six minute walk test.