Influence of reduced airway patency and respiratory muscle strength on autonomic cardiac modulation in COPD patients

Introduction: Chronic obstructive pulmonary disease (COPD) is characterized by lower small airway patency and reduced respiratory and peripheral muscle strength. COPD induces changes in the sympatho-vagal balance, which a reduction in heart rate variability (HRV), associated with increased morbidity and mortality. Purpose: To investigate the influence of airway permeability and expiratory muscle strength on autonomic cardiovascular control in COPD patients. Methods: 52COPD patients (age=67±4 years; FEV 1 % predicted=40.9±15.7) participated in the study. The forced expiratory flow between 25% and 75% of vital capacity (FEF 25-75% ) and the FEF 25-75% as a percentage of the predicted value (FEF 25-75% P), that reflect small airway patency, and the maximal expiratory pressure (MEP), a marker of expiratory muscle strength (EMS), were measured. The HRV signal was recorded in supine position and the HRV power in the high frequency band (HF) and the Poincare index SD2, both markers of sympathetic activation, were computed. A Spearman9s correlation analysis was conducted between FEF 25-75% , FEF 25-75% P, MEP, and HRV indices. Results: Lower FEV 25-75% and FEV 25-75% P values were significantly associated with higher HF values (r=-0.41 and r=-0.39, respectively) and higher SD2 values (r=-0.40 and r=-0.40, respectively). Lower MEP values were associated with higher HF values (r=-0.32) and higher SD2 values (r=-0.42). Conclusion: In COPD patients lower airway patency and expiratory strength are associated during rest with a greater alteration in autonomic cardiac modulation, with stronger sympathetic activation. Supported by CAPES no 88881.062123/2014-01 and by FAPESP no 2013/23013-0.