Cardiovascular responses to low-level transcutaneous vagus nerve stimulation

Aims: The aim was to determine cardiovascular responses to an arbitrary protocol of transcutaneous low-level vagus nerve electrical stimulation (tVNS). Methods: Study was performed in 15 male volunteers, mean age 23 years. Data were collected during two sessions - sham stimulation (no stimulation) and stimulation. Each session included one-hour resting phase followed by 15-min autonomic nervous system testing phase (Valsalva, deep breathing, wet-cold face tests), all in supine position. The right tragus stimulation parameters were: 20 Hz, constant current at sensation threshold, 1 ms rectangular pulse width. The ECG, noninvasive arterial blood pressure and thoracic impedance cardiography measurements were recorded and analyzed continuously with the Task Force (R) Monitor (CNSystems Medizintechnik GmbH, Graz, Ver. 2.2.10.0). t-Test for paired samples, paired Wilcoxon signed-rank, and one-way ANOVA for repeated measurements were carried out. P < 0.05 was considered significant. Results: We demonstrated significant reductions of left ventricular contractility and output parameters, a trend for heart rate reduction, and resulting beneficial reduction of left ventricular work load. However, significant increases of blood pressure and total peripheral resistance were recognized, possibly as a reflex response. Conclusion: It seems that our tVNS protocol has a potential for cardiac autonomic modulation. This gives us opportunity to advance our stimulation parameters with participant-specific adjustments. Further studies are however needed to prove the therapeutic potential of such approach in different patient groups.