Gender Differences in Short-Term Multiscale Complexity of the Heart Rate Variability

Among the analytical methods estimating the complexity of the heart period (HP), the linear model-based multiscale complexity (MSC) approach allows the estimation of the complexity over time scales linked to the cardiac autonomic control, i.e. in the low frequency (LF, 0.04-0.15 Hz) and high frequency $(HF,\ 0.15-0.4\ Hz)$ bands. In this study we exploited MSC to evaluate the differences in the HP variability complexity during daytime (DAY) and nighttime (NIGHT) in 23 healthy females (WOMEN, age $36\pm 6yrs)$ ) and 21 males (MEN, age $35\pm 5yrs)$ performing a 24-hour Holter electrocardiogram. Parametric power spectral analysis was applied as well for comparison. Complexity indexes were computed regardless of the temporal scale (CI) and in the LF and HF bands ( $CI_{LF}$ and $CI_{HF}$, respectively). We found that the power spectral indexes did not differentiate WOMEN and MEN, while CI and $CI_{LF}$ were higher in WOMEN during DAY. The higher HP complexity in females could be explained by a lower sympathetic drive and more complex hormonal regulation than males. We conclude that MSC was more powerful than power spectral analysis in detecting gender differences in HP variability. In addition, as cardiac control differs between females and males, preventive and therapeutic interventions should take gender differences into account.