RESUMO
(Appeared originally in Brain Stimulation 2018; 11:492-500) Reprinted with permission from Elsevier.
RESUMO
BACKGROUND: Optimal parameters of transcutaneous auricular vagus nerve stimulation (taVNS) are still undetermined. Given the vagus nerve's role in regulating heart rate (HR), it is important to determine safety and HR effects of various taVNS parameters. OBJECTIVE: We conducted two sequential trials to systematically test the effects of various taVNS parameters on HR. METHODS: 15 healthy individuals participated in the initial two-visit, crossover exploratory trial, receiving either tragus (active) or earlobe (control) stimulation each visit. Nine stimulation blocks of varying parameters (pulse width: 100⯵s, 200⯵s, 500⯵s; frequency: 1â¯Hz, 10â¯Hz, 25â¯Hz) were administered each visit. HR was recorded and analyzed for stimulation-induced changes. Using similar methods and the two best parameters from trial 1 (500µs 10â¯Hz and 500µs 25â¯Hz), 20 healthy individuals then participated in a follow-up confirmatory study. RESULTS: Trial 1- There was no overall effect of the nine conditions on HR during stimulation. However multivariate analysis revealed two parameters that significantly decreased HR during active stimulation compared to control (500µs 10â¯Hz and 500µs 25â¯Hz; pâ¯<â¯0.01). Additionally, active taVNS significantly attenuated overall sympathetic HR rebound (post-stimulation) compared to control (pâ¯<â¯0.001). Trial 2-For these two conditions, active taVNS significantly decreased HR compared to control (pâ¯=â¯0.02), with the strongest effects at 500µs 10â¯Hz (pâ¯=â¯0.032). CONCLUSION: These studies suggest that 60s blocks of tragus stimulation are safe, and some specific parameters modulate HR. Of the nine parameters studied, 500µs 10â¯Hz induced the greatest HR effects.
Assuntos
Frequência Cardíaca , Estimulação Elétrica Nervosa Transcutânea/efeitos adversos , Estimulação do Nervo Vago/efeitos adversos , Adulto , Humanos , Masculino , Estimulação Elétrica Nervosa Transcutânea/métodos , Nervo Vago/fisiologia , Estimulação do Nervo Vago/métodosRESUMO
BACKGROUND: Electrical stimulation of the auricular branch of the vagus nerve (ABVN) via transcutaneous auricular vagus nerve stimulation (taVNS) may influence afferent vagal networks. There have been 5 prior taVNS/fMRI studies, with inconsistent findings due to variability in stimulation targets and parameters. OBJECTIVE: We developed a taVNS/fMRI system to enable concurrent electrical stimulation and fMRI acquisition to compare the effects of taVNS in relation to control stimulation. METHODS: We enrolled 17 healthy adults in this single-blind, crossover taVNS/fMRI trial. Based on parameters shown to affect heart rate in healthy volunteers, participants received either left tragus (active) or earlobe (control) stimulation at 500⯵s 25â¯HZ for 60â¯s (repeated 3 times over 6â¯min). Whole brain fMRI analysis was performed exploring the effect of: active stimulation, control stimulation, and the comparison. Region of interest analysis of the midbrain and brainstem was also conducted. RESULTS: Active stimulation produced significant increased BOLD signal in the contralateral postcentral gyrus, bilateral insula, frontal cortex, right operculum, and left cerebellum. Control stimulation produced BOLD signal activation in the contralateral postcentral gyrus. In the active vs. control contrast, tragus stimulation produced significantly greater BOLD increases in the right caudate, bilateral anterior cingulate, cerebellum, left prefrontal cortex, and mid-cingulate. CONCLUSION: Stimulation of the tragus activates the cerebral afferents of the vagal pathway and combined with our review of the literature suggest that taVNS is a promising form of VNS. Future taVNS/fMRI studies should systematically explore various parameters and alternative stimulation targets aimed to optimize this novel form of neuromodulation.