Associations between symbolic heart rate variability indices and submaximal functional performance in individuals with moderate-to-severe COPD: An observational study

Chronic obstructive pulmonary disease (COPD) is associated with reduced functional capacity and impaired autonomic cardiovascular regulation. Heart rate variability (HRV), assessed using spectral and symbolic analyses, provides insight into autonomic function, but its relationship with functional performance- particularly during submaximal exercise is not well established. The objective of this study was to evaluate the association between resting HRV, assessed by symbolic and spectral methods, and submaximal performance obtained by six-minute walking test (6MWT) in individuals with COPD compared with healthy controls. Adults with moderate-to-severe COPD and healthy controls (HCs) underwent spirometry, dyspnea assessment, and measurement of maximal respiratory pressures. Functional capacity was evaluated using 6MWT. Resting HRV was described via indexes in time-domain and frequency-domain. Symbolic analyses was applied as well. Correlation and multiple linear regression analyses were used to examine associations between HRV indices and 6MWT distance. Thirty-two participants with COPD and twelve controls were included. Compared with HCs, individuals with COPD showed reduced pulmonary function, lower respiratory muscle strength, and shorter 6MWT distance. COPD group exhibited higher SE and lower percentage of symbolic patterns with no variation (0 V%). In COPD, SE was negatively associated with 6MWT distance, while 0 V% showed a weak positive association. In HCs, Poincaré plot indexes correlated positively with 6MWT distance. In the COPD group, SE and forced vital capacity emerged as independent predictors of 6MWT in COPD, explaining 39% of its variance (adjusted R 2 = 0.391). In COPD, impaired autonomic complexity is associated with poorer submaximal performance.