Cardiac and sympathetic baroreflex sensitivity is not affected by transcutaneous vagus nerve stimulation in hyperadrenergic postural tachycardia syndrome

Hyperadrenergic postural tachycardia syndrome (HyperPOTS) is characterized by a shift of the sympatho- vagal balance toward sympathetic predominance. Transcutaneous vagus nerve stimulation (tVNS) might be beneficial in HyperPOTS, although the acute effects of tVNS on baroreflex sensitivity (BRS) are still unclear. We concomitantly evaluated BRS in the cardiac (cBRS) and sympathetic (sBRS) baroreflex arms in 19 HyperPOTS patients (39±11 yrs; 17 females) undergoing 75° head-up tilt test (HUT) during two randomized tVNS sessions with the device switched off and switched on. Variability of heart period (HP), systolic and diastolic arterial pressure (SAP and DAP), and muscle nerve sympathetic activity (MSNA) burst rate were extracted simultaneously from the ECG, arterial pressure and MSNA signals. cBRS and sBRS were estimated as the transfer function gain respectively from SAP to HP and from DAP to MSNA burst rate in the low (0.04-0.15 Hz) frequency band. cBRS significantly decreased during HUT but did not vary across tVNS sessions, while both HUT and tVNS had no impact on sBRS. We conclude that the acute effect of a single tVNS session on the sensitivity of different baroreflex arms is negligible in HyperPOTS, while HUT only seems to affect cBRS, potentially due to the HyperPOTS baseline sympathetic overactivity.