Respiratory muscle strength effect on linear and nonlinear heart rate variability parameters in COPD patients

Abstract

Introduction: Chronic obstructive pulmonary disease (COPD) is recognized as a multisystemic inflammatory disease associated with extrapulmonary comorbidities, including respiratory muscle weakness and cardiovascular and cardiac autonomic regulation disorders. We investigated whether alterations in respiratory muscle strength (RMS) would affect cardiac autonomic modulation in COPD patients.

Methods: This study was a cross-sectional study done in ten COPD patients affected by moderate to very severe disease. The heart rate variability (HRV) signal was recorded using a Polar cardiofrequencimeter at rest in the sitting position (10 minutes) and during a respiratory sinus arrhythmia maneuver (RSA-M; 4 minutes). Linear analysis in the time and frequency domains and nonlinear analysis were performed on the recorded signals. RMS was assessed using a digital manometer, which provided the maximum inspiratory pressure (PImax) and the maximum expiratory pressure (PEmax).

Results: During the RSA-M, patients presented an HRV power increase in the low-frequency band (LFnu) (46.9±23.7 vs 75.8±27.2; P=0.01) and a decrease in the high-frequency band (HFnu) (52.8±23.5 vs 24.0±27.0; P=0.01) when compared to the resting condition. Significant associations were found between RMS and HRV spectral indices: PImax and LFnu (r=-0.74; P=0.01); PImax and HFnu (r=0.74; P=0.01); PEmax and LFnu (r=-0.66; P=0.01); PEmax and HFnu (r=0.66; P=0.03); between PEmax and sample entropy (r=0.83; P<0.01) and between PEmax and approximate entropy (r=0.74; P=0.01). Using a linear regression model, we found that PImax explained 44% of LFnu behavior during the RSA-M.

Conclusion: COPD patients with impaired RMS presented altered cardiac autonomic control, characterized by marked sympathetic modulation and a reduced parasympathetic response; reduced HRV complexity was observed during the RSA-M.

Keywords: COPD; autonomic nervous system; heart rate; muscle strength; sinus arrhythmia.

Figure 1

Moderate-to-strong correlations were found between PImax and PEmax, and spectral HRV indices during the RSA-M. Notes: (A) Negative correlation between LF (nu) and PImax (cm H₂O); (B) negative correlation between LF (nu) and PEmax (cm H₂O); (C) positive correlation between HF (nu) and PImax (cm H₂O); (D) Positive correlation between HF (nu) and PEmax (cm H₂O). The Spearman’s correlation analysis was performed. Significance level: P≤0.05. Abbreviations: HRV, heart rate variability; RSA-M, respiratory sinus arrhythmia maneuver; HF, power in the high-frequency band; LF, power in the low-frequency band; PImax, maximum inspiratory pressure; PEmax, maximum expiratory pressure; nu, normalized units; cm H₂O, centimeters of water.

Figure 2

Strong correlations were also observed between HRV complexity indices (ApEn and SampEn) and PEmax during the RSA-M. Notes: (A) Positive correlation between SampEn and PEmax (cm H₂O); (B) Positive correlation between ApEn and PEmax (cm H₂O). The Spearman’s correlation analysis was performed. Significance level: P≤0.05. Abbreviations: HRV, heart rate variability; RSA-M, respiratory sinus arrhythmia maneuver; PEmax, maximum expiratory pressure; SampEn, sample entropy; ApEn, approximate entropy; cm H₂O, centimeters of water.