Multiscale multifractality of heart rate variability: role of autonomic control

Heart rate variability (HRV) reflects the complex interplay of physiological systems, like the autonomic nervous system, which modulates HRV through parasympathetic and sympathetic branches. This study investigates the multiscale multifractal properties of HRV and the influence of autonomic control using an optimized Detrended Fluctuation Analysis (DFA) framework. Building on prior work, we applied a multifractal multiscale DFA to series of cardiac intervals recorded in 9 healthy volunteers before and during selective autonomic blocks (parasympathetic, sympathetic, combined, and central sympathetic). We quantified fractal components over the scales between 9 and 120 s, using moment orders from – 5 to +5 to differentiate between low- and high-amplitude fluctuations. Results reveal that HRV exhibits intrinsic multiscale multifractality, with distinct scale-dependent patterns for different amplitude components. Autonomic blocks alter these patterns: parasympathetic blockade significantly increases the coefficients at scales shorter than 30 s for high-amplitude components and between 20 and 50 s for low-amplitude components, and sympathetic blockade decreases the coefficients at scales around 50 s for the high-amplitude components. Furthermore, unlike sympathetic blockade, parasympathetic blockade increases the degree of multiscale multifractality. This suggests that the multifractal dynamics of high-amplitude components arise from the superposition of autonomic influences with distinct transfer functions—flat for vagal and low-pass for sympathetic modulation; and that the parasympathetic outflow may also contribute to the multifractality of low-amplitude components. In conclusion, this study underscores the potential of multiscale multifractal analysis in characterizing cardiovascular control and the valuable insights it may offer for diagnosing dysautonomia and monitoring therapeutic interventions.