Relationship between linear and nonlinear dynamics of heart rate and impairment of lung function in COPD patients

Abstract

Background: In chronic obstructive pulmonary disease (COPD), functional and structural impairment of lung function can negatively impact heart rate variability (HRV); however, it is unknown if static lung volumes and lung diffusion capacity negatively impacts HRV responses. We investigated whether impairment of static lung volumes and lung diffusion capacity could be related to HRV indices in patients with moderate to severe COPD.

Methods: Sixteen sedentary males with COPD were enrolled in this study. Resting blood gases, static lung volumes, and lung diffusion capacity for carbon monoxide (DLCO) were measured. The RR interval (RRi) was registered in the supine, standing, and seated positions (10 minutes each) and during 4 minutes of a respiratory sinus arrhythmia maneuver (M-RSA). Delta changes (Δsupine-standing and Δsupine-M-RSA) of the standard deviation of normal RRi, low frequency (LF, normalized units [nu]) and high frequency (HF [nu]), SD1, SD2, alpha1, alpha2, and approximate entropy (ApEn) indices were calculated.

Results: HF, LF, SD1, SD2, and alpha1 deltas significantly correlated with forced expiratory volume in 1 second, DLCO, airway resistance, residual volume, inspiratory capacity/total lung capacity ratio, and residual volume/total lung capacity ratio. Significant and moderate associations were also observed between LF/HF ratio versus total gas volume (%), r=0.53; LF/HF ratio versus residual volume, %, r=0.52; and HF versus total gas volume (%), r=-0.53 (P<0.05). Linear regression analysis revealed that ΔRRi supine-M-RSA was independently related to DLCO (r=-0.77, r (2)=0.43, P<0.05).

Conclusion: Responses of HRV indices were more prominent during M-RSA in moderate to severe COPD. Moreover, greater lung function impairment was related to poorer heart rate dynamics. Finally, impaired lung diffusion capacity was related to an altered parasympathetic response in these patients.

Keywords: COPD; cardiac autonomic nervous system; heart rate variability; lung diffusion capacity; rest hyperinflation; static lung volumes.

Figure 1

Comparison of heart rate variability indices among supine-stand, supine-sitting, and sitting-M-RSA maneuvers. Notes: *P<0.05 between supine-stand and sitting-M-RSA maneuvers; **P<0.05 between supine-sitting and sitting-M-RSA maneuvers. Abbreviations: M-RSA, respiratory sinus arrhythmia maneuver; SDNN, standard deviation of the normal RR intervals; RMSSD, square root of the sum of the squares of differences adjacent normal RR intervals; LF (nu), low frequency in normalized units; HF (nu), high frequency in normalized units; SD1, standard deviation measuring dispersion of points in the plot perpendicular to the line-of-identity; SD2, standard deviation measuring dispersion of points along the line-of-identity; alpha1, short-term fluctuations of detrended fluctuation analysis; alpha2, long-term fluctuations of detrended fluctuation analysis; ApEn, approximate entropy.

Figure 2

Correlation between HRV indices (deltas) and variables from lung function tests. Data are presented as the correlation coefficient (r). Notes: *P<0.05. Δsupine-sitting, HRV index in supine position minus HRV index in seated position; Δsitting-M-, HRV index in seated position minus HRV index during M-RSA. Abbreviations: M-RSA, respiratory sinus arrhythmia maneuver; HF (nu), high frequency in normalized units; SD1, standard deviation measuring dispersion of points in the plot perpendicular to the line-of-identity; SD2, standard deviation measuring dispersion of points along the line-of-identity; alpha1, short-term fluctuations of detrended fluctuation analysis; FEV₁, forced expiratory volume in 1 second; DL_CO, diffusion lung capacity for carbon monoxide; Raw, airway resistance; RV, residual volume; IC/TLC, inspiratory capacity/total lung capacity ratio; RV/TLC, residual volume/total lung capacity ratio; HRV, heart rate variability.

Figure 3

Correlation between heart rate variability indices (absolute values) and variables from lung function tests. Note: *P<0.05. Abbreviations: LF/HF, low frequency/high frequency ratio; HF (nu), high frequency in normalized units; TGV, total gas volume; RV, residual volume.

Figure 4

Backward linear regression. Note: *P<0.05. Abbreviations: DL_CO, diffusion lung capacity for carbon monoxide; ΔRRi sitting-M-RSA, RRi in seated position minus RRi during M-RSA; SEE, standard error of estimate.