Role of heart rate variability analysis in differentiating patients with idiopathic REM sleep behaviour disorders from healthy subjects. A systematic review with meta-analysis

Introduction: Autonomic nervous system (ANS) alteration has been acknowledged for disrupted sleep and α-synucleopaties. Since idiopathic REM sleep behavior disorder (iRBD) precedes α-synucleopaties, ANS function indices could predict conversion. Heart rate variability (HRV) analysis could better define cardiac ANS in iRBD. This systematic review with meta-analysis purpose was to investigate the HRV indices role in differentiating iRBD and controls. Method: Included studies (three databases screened) compare HRV indices in iRBD and controls during REM, non-REM (NREM) or wake phases. Outcomes included HRV indices in time and frequency domains. Meta-analysis performed for HRV indices computed standardized mean difference with 95 % confidence intervals. Results: The 22 included studies had unbalanced age groups, mostly composed of males. An overall lower HRV and cardiac vagal modulation emerged in iRBD. Almost all studies evaluated HRV parameters only during wakefulness and most of those separated NREM and REM phases, better highlighting differences between iRBD and controls. Conclusion: Results suggest an overall reduced HRV and cardiac vagal modulation in iRBD patients. Furthermore, separated analysis of the different sleep stages better differentiate subjects with iRBD. Further longitudinal studies on larger populations would reach more conclusions defining relationships between HRV and neurodegenerative diseases in prodromic stages.