RESUMO
BACKGROUND: Transcutaneous auricular vagus nerve stimulation (taVNS) may modulate cardiac autonomic function. However, the response rate of the traditional tonic paradigm is low, and the results remain inconsistent. A recent pilot study presented a novel burst paradigm to activate the cardiac parasympathetic system, which might offer a new approach to treat cardiac autonomic function. The present study reassessed the effect of burst taVNS on modulating heart rate variability and explored the difference between burst and traditional tonic paradigms. MATERIALS AND METHODS: Forty-two young adults were recruited for this study. Each participant underwent three types of taVNS with sham (30 sec of stimulation), tonic (25 Hz, 500 µsec), and burst (five pulses at 500 Hz every 200 msec) paradigms, respectively, with simultaneous electrocardiogram recording. One-way analysis of variance, multivariate analysis of variance, and linear regression were used for analysis. Multiple testing was performed using Bonferroni correction. RESULTS: Both burst and tonic paradigms induced a significant decrease in heart rate, which continued until poststimulation, and increased cardiac parasympathetic activity. Moreover, two parasympathetic system indicators showed significant increase only in burst taVNS. The response rates during burst (35.7%) and tonic (38.1%) stimulations were both higher than that during sham stimulation (11.9%). The response to taVNS showed parameter specificity with few nonresponders to the tonic paradigm responding to the burst paradigm. The overall response rate increased from 38.1% in tonic taVNS to 54.8% in taVNS using both burst and tonic paradigms. For both burst and tonic responders, baseline cardiac parasympathetic activity was found to be significantly negatively correlated with changes during stimulation. CONCLUSION: The burst parameter could be used as an alternative strategy for regulating cardiac parasympathetic function by taVNS, which has the potential to be used as a complementary paradigm to traditional tonic taVNS for promoting clinical treatment efficacy.