Association between heart rate variability and cardiorespiratory fitness in individuals with type 2 diabetes mellitus

Abstract

Background: Type 2 Diabetes Mellitus (T2DM) is associated with cardiovascular risk, which is partly due to autonomic dysfunction and decreased cardiorespiratory fitness. This study examines the relationship between heart rate variability (HRV) and maximal oxygen uptake (VO2max) in T2DM patients to understand their interconnected impacts on autonomic and aerobic functions. Methods: In a cross-sectional study, 77 T2DM patients underwent HRV and VO2max assessments using standard protocols. HRV metrics were analysed in conjunction with VO2max, measured through direct breath-by-breath analysis. Pearson's correlation coefficient was used to investigate the relationships between HRV indices and VO2max. Results: VO2max showed strong positive correlations with RMSSD (r = 0.89, p < .001), HF (r = 0.54, p < .001), and pNN50% (r = 0.52, p < .001), indicating higher parasympathetic activity with improved cardiorespiratory fitness. Negative correlations with LF (r = -0.60, p < .001) and the LF/HF ratio (r = -0.39, p < .001) suggested that better fitness levels lead to sympathetic withdrawal and a more favourable autonomic balance. Moderate positive correlations with SDNN (r = 0.46, p < .001) and TP (r = 0.58, p < .001) further suggested that overall autonomic modulation is enhanced with increased cardiorespiratory fitness. Conclusion: This study substantiates a significant correlation between HRV and VO2max in individuals with T2DM, highlighting the intricate relationship between autonomic function and aerobic capacity. These findings suggest that enhancing cardiorespiratory fitness may improve autonomic balance, offering potential avenues for mitigating cardiovascular risk in the T2DM population.