Acute transcutaneous auricular vagus nerve stimulation is associated with lower baroreflex sensitivity without detectable Mayer-wave coherence change: an exploratory study

Abstract Transcutaneous auricular vagus nerve stimulation (taVNS) delivers afferent inputs, but cardiovascular responses are heterogeneous and autonomic outcomes are not interchangeable. In this exploratory, non-randomised, open-label study, 18 healthy men completed fixed-order five-minute Pre, left-cymba Stim, and Post phases without sham. Spontaneous sequence baroreflex sensitivity (BRS seq, all ; designated centrally post hoc) was lower during Stim than Pre (8.54 ± 5.57 versus 6.49 ± 3.89 ms/mmHg; paired mean difference − 2.05, BCa 95% CI − 3.81 to − 1.10; Wilcoxon p = 2.29 × 10 − 5 ; Cohen’s d z = − 0.74), with negative differences in 17/18 participants. Mayer-band coherence and representative heart rate variability indices showed no detectable Stim–Pre differences. Systolic blood pressure was higher during Stim. Recovery of BRS was not established. No adverse events were reported after the sessions. Sequence BRS estimates blood pressure–R–R interval gain, whereas heart rate variability and coherence quantify different properties. This pattern supports prospective evaluation of sequence BRS as a session-level physiological response measure. The design does not establish stimulation-specific engagement, direct vagal inhibition, clinical utility, or a monitoring threshold. Sham-controlled replication is required. Trial registration: Japan Registry of Clinical Trials (jRCT), jRCT1032230440. Registered on 9 November 2023.