Assessment of Sleep-wake State-associated Dynamic Changes in Heart Rate Variability in Female Rat: Autonomic System Modelling Approaches for Studying Behavioural Dysregulation.

Background: Acute heart rate variability (HRV) is used for assessment of functional autonomic profile in awake resting state in humans subjects. Evaluation of 24-h variations in the sympatho-vagal balance across sleep stages through HRV are valuable to understand the basis of various lifestyles diseases, however, such studies are uncommon. Purpose: The present study modelled the sleep-wake associated cardiac autonomic changes in freely moving female Wistar rats across light and dark phase using HRV as a tool. Methods: Sleep states (non-rapid eye movement [NREM] and rapid eye movement [REM] sleep) were estimated through electroencephalogram (EEG) and electromyogram (EMG), while the ECG signal was acquired simultaneously for HRV analysis. To understand circadian dynamics, HRV was analysed for noise-free distinct and transitional state segments of sleep-wakefulness. Results: In time domain parameters, RR intervals during NREM sleep were longer in comparison to wake and REM sleep. In the frequency domain, reductions in LF and an increase in HF power during NREM sleep were evident compared to other states. RR interval during wakefulness in the dark phase was significantly decreased compared to the light phase. The RR interval was the longest during the early phase of the light period (6-10 am) in all three states. Conclusion: Parasympathetic predominance during NREM sleep was similar to a human having a monophasic pattern, while a higher sympathetic tone during the majority of transitional states in rats, which are polyphasic in nature, indicated risk of dysregulated sympatho-vagal balance with fragmented sleep. Further, the highest parasympathetic activity during the early light phase and the highest sympathetic drive during the dark phase may serve as an adaptive mechanism for survival in nocturnal life.