Hemodynamic responses to low-level transcutaneous auricular nerve stimulation in young volunteers

The aim of this study was to characterize cardiovascular autonomic responses during two constant current intensities below sensory threshold of transcutaneous auricular nerve stimulation (taNS). On this basis, a protocol for taNS with autonomic modulatory potential could be proposed.

We included 26 men and 24 women, mean age 26. Data were collected during three randomly allocated 20-minute right tragus stimulation sessions - a) no-stimulation (sham), b) 90 µA (arbitrary), and c) 130 µA (near the lowest sensory threshold in majority). Stimulation was 20 Hz, rectangular pulse width of 2 ms, duty cycle 2-second on/off. To assess autonomic responses, we continuously recorded ECG, non-invasive arterial blood pressure (BP) and thoracic impedance cardiography data. Ten-minute data were compared. Fast Fourier transform of RR intervals was performed on 10-minute recordings as well. Low frequency and high frequency power spectra were calculated. Friedman test or one-way ANOVA for repeated measurements and Mann-Whitney or Wilcoxon's signed-rank test, or t-test were carried out. P < 0.05 was considered significant.

At 130 µA stimulation, cardiac output significantly decreased (p < 0.05), driven by significant heart rate drop in women, and stroke volume and contractility drop in men, pointing to a gender-related autonomic responses. We observed no significant changes in BP, or variability parameters. Significantly higher body size and BP were found in men, as expected.

It seems that tested taNS protocol has a potential for cardiac autonomic modulation in majority of young healthy men as well as women. Further studies are however needed to prove the therapeutic potential of this stimulation protocol in different patient groups.