Influence of expiratory positive airway pressure on cardiac autonomic modulation at rest and in submaximal exercise in COPD patients

Abstract

The aim of this study was to evaluate the effect of expiratory positive airway pressure (EPAP) on heart rate variability (HRV) indices at rest and during 6-min walk test (6MWT) in chronic obstructive pulmonary disease (COPD) patients. Fifteen moderate to severe COPD patients were randomized and evaluated with and without (Non-EPAP) a 5 cmH2O EPAP device. Respiratory rate (RR) was collected at rest (5 min), during the 6MWT (5 min), and at recovery (5 min). Indices of HRV were computed in the time domain, in the frequency domain, and nonlinear analysis. For EPAP and Non-EPAP during the 6MWT, we found an increased mean heart rate (HR) (P=0.001; P=0.001) while mean RR (P=0.001; P=0.015) and RR tri index decreased (P=0.006; P=0.028). Peripheral oxygen saturation (P=0.019) increased at rest only in the EPAP group. In EPAP, correlations were found between forced expiratory volume in 1 s (FEV1) and low frequency (LF) sympathetic tonus (P=0.05; r=-0.49), FEV1 and high frequency (HF) parasympathetic tonus at rest (P=0.05; r=0.49), lactate at rest and LF during the 6MWT (P=0.02; r=-0.57), and lactate at rest and HF during 6MWT (P=0.02; r=0.56). Through a linear regression model, we found that lactate at rest explained 27% of the alterations of LF during 6MWT. The use of 5 cmH2O EPAP improved autonomic cardiac modulation and its complexity at rest in COPD patients. Although it did not influence the performance of the 6MWT, the EPAP device caused alterations in resting lactate concentration with an effect on sympatho-vagal control during the test.

Figure 1.. Flowchart of sampling and study phases. COPD: chronic obstructive pulmonary disease; 6MWT: 6-min walk test; EPAP: positive airways pressure.

Figure 2.. A, Peripheral oxygen saturation, and B, distance walked in the 6 min walk test in positive airways pressure (EPAP) and Non-EPAP groups of chronic obstructive pulmonary disease patients. Student's t-test was used for statistical analyses. Vertical lines indicate means and SDs.

Figure 3.. Relationship between lung function and heart rate variability index at rest. A, Negative correlation between LF (nu) and FEV₁ (% of predicted). B, Positive correlation between HF (nu) and FEV₁ (% of predicted). The Pearson correlation analysis was used for statistical analyses. FEV₁: forced expiratory volume in 1 s; LF: low frequency; HF: high frequency; nu: normalized units.

Figure 4.. Relationship between lactate and heart rate variability index during 6-min walk test (6MWT). A, Negative correlation between LF (nu) and lactate at rest (mmol/L) with expiratory positive airway pressure (EPAP). B, Positive correlation between HF (nu) during 6MWT and lactate (mmol/L) at rest with EPAP. C, Positive correlation between LF (nu) during 6MWT and lactate (mmol/L) at rest in Non-EPAP. D, Negative correlation between HF (nu) during 6MWT and lactate (mmol/L) at rest in Non-EPAP. Pearson correlation analysis was performed. LF: low frequency; HF: high frequency; nu; normalized units.