Daytime autonomic activity in idiopathic rapid eye movement sleep behavior disorder: a preliminary study

Ojective: To investigate cardiovascular and sudomotor autonomic functions in patients with idiopathic rapid eye movement (REM) sleep behavior disorder (iRBD) during wakefulness compared to patients with Parkinson's disease (PD) and healthy subjects. Methods: Drug-naïve iRBD patients, PD patients and healthy controls underwent cardiovascular function tests including head-up tilt test (HUTT), Valsalva maneuver, deep breathing, hand grip, and cold face. Heart rate variability (HRV) analysis was performed in the frequency domain using an autoregressive algorithm in the rest supine condition and during HUTT. Sudomotor function was assessed through Sudoscan. Results: Fourteen iRBD patients, 17 PD patients and 12 healthy controls were included in the study. In the supine resting condition, the baseline values of systolic and diastolic blood pressure and heart rate were comparable in all groups. At Valsalva maneuver, iRBD patients and PD patients showed an overshoot which was significantly lower than controls. In addition, iRBD patients showed a significant reduction of sinus arrhythmia at deep breathing compared to controls. Cardiovascular responses to cold face were similar in the three groups while isometric handgrip was significantly reduced in PD patients with respect to healthy subjects. Spectral analysis of HRV showed no significant differences among iRBD, PD patients and controls in the supine resting condition; whereas during HUTT the low-frequency (LF) component of HRV was significantly higher in controls with respect to iRBD and the high-frequency (HF) component was significantly higher in iRBD patients compared to controls. In addition, a significant increase in the LF/HF ratio in healthy subjects was detected compared to iRBD. Finally, four out of 14 iRBD patients (29%) and nine of 17 PD patients (53%) had a sudomotor dysfunction. Conclusions: Our findings obtained in de novo iRBD and PD patients indicate that some alterations of the autonomic nervous system are shared by both groups of patients, reinforcing the close link between the two pathologies, and show an autonomic fragility during wakefulness in iRBD that mainly arises under stress conditions.