Abstract
Previous work has suggested that transcutaneous vagus nerve stimulation (tVNS) of the auricular branch of the vagus nerves might be associated with symptom relief pre-operatively and fewer complications after surgery. Recent studies have also shown improvements in heart rate variability (HRV) after tVNS in healthy subjects, but there is limited published data. The aim of this study was to compare the acute effects of tVNS with sham stimulation on respiration and HRV.
Thirty healthy subjects were recruited and gave written informed consent. The study was approved by the Science and Engineering Ethical Committee and was in accordance with the Declaration of Helsinki. Inclusion criteria was 18-65 year old healthy adults. Exclusion criteria was previous history of neuromuscular, autonomic, cardiorespiratory or ear skin conditions. Subjects completed a questionnaire, anthropometry and resting blood pressure, heart rate, and oxygen saturation measurements. Each participant completed three randomized interventions, each having a rest (10 minutes), stimulation (15 minutes), and recovery period (10 minutes), therefore, they completed nine consecutive experiments supine.
Electrical stimulation was delivered by placing an electrode clip to the auricular branch of the vagus nerve on the tragus of the external ear, earlobe, or thenar web space (the space between the thumb and index finger), using a commercial non-invasive transcutaneous electrical nerve stimulation (TENS) device. Electrodes were applied bilaterally, with the amplitude gradually adjusted until just below participants’ level of sensory perception. The earlobe and the web space simulated sham stimulation, occurring at two different anatomical locations, relative to the tragus. During the stimulation, the electrocardiogram, heart rate variability, breathing rate (BR) and skin temperature were measured with Equivital wireless physiological monitoring equipment using LabChart software. HRV was assessed using time domain (heart rate – HR, standard deviation of the RR interval – SDRR) and frequency domain (low and high frequency – LF and HF). Data were statistically analysed for the complete time, the first and last five minutes, by repeated measures ANOVA, using SPSS. P<0.05 was considered as significant.
Results were analyzed over all nine experiments. SDRR showed a significant increase (P<0.05) for the first five minutes. Over the complete time, skin temperature (P<0.0001) significantly increased. HR, LF, HF, LF/HF ratio, BR (P>0.05) were not significantly different.
The primary findings of our investigation showed that tVNS & other sham site stimulation largely did not have a significant effect on the HRV, HR or BR, demonstrating that tVNS is not effective in modifying these aspects of autonomic function in our subjects. One reason our subjects did not show a marked vagal cardiorespiratory effect of tVNS could be due to their younger age (mean SD = 27.8 (12.1) years), relative to previous work. A steady increase in temperature across the interventions could have been due to a cold couch the subjects were lying on. This investigation includes limitations such as the small population size and a varied TENS neuro-sensitivity threshold. In conclusion, these findings provide a potential foundation for further research into the effects of tVNS and possible clinical applications.
Thirty healthy subjects were recruited and gave written informed consent. The study was approved by the Science and Engineering Ethical Committee and was in accordance with the Declaration of Helsinki. Inclusion criteria was 18-65 year old healthy adults. Exclusion criteria was previous history of neuromuscular, autonomic, cardiorespiratory or ear skin conditions. Subjects completed a questionnaire, anthropometry and resting blood pressure, heart rate, and oxygen saturation measurements. Each participant completed three randomized interventions, each having a rest (10 minutes), stimulation (15 minutes), and recovery period (10 minutes), therefore, they completed nine consecutive experiments supine.
Electrical stimulation was delivered by placing an electrode clip to the auricular branch of the vagus nerve on the tragus of the external ear, earlobe, or thenar web space (the space between the thumb and index finger), using a commercial non-invasive transcutaneous electrical nerve stimulation (TENS) device. Electrodes were applied bilaterally, with the amplitude gradually adjusted until just below participants’ level of sensory perception. The earlobe and the web space simulated sham stimulation, occurring at two different anatomical locations, relative to the tragus. During the stimulation, the electrocardiogram, heart rate variability, breathing rate (BR) and skin temperature were measured with Equivital wireless physiological monitoring equipment using LabChart software. HRV was assessed using time domain (heart rate – HR, standard deviation of the RR interval – SDRR) and frequency domain (low and high frequency – LF and HF). Data were statistically analysed for the complete time, the first and last five minutes, by repeated measures ANOVA, using SPSS. P<0.05 was considered as significant.
Results were analyzed over all nine experiments. SDRR showed a significant increase (P<0.05) for the first five minutes. Over the complete time, skin temperature (P<0.0001) significantly increased. HR, LF, HF, LF/HF ratio, BR (P>0.05) were not significantly different.
The primary findings of our investigation showed that tVNS & other sham site stimulation largely did not have a significant effect on the HRV, HR or BR, demonstrating that tVNS is not effective in modifying these aspects of autonomic function in our subjects. One reason our subjects did not show a marked vagal cardiorespiratory effect of tVNS could be due to their younger age (mean SD = 27.8 (12.1) years), relative to previous work. A steady increase in temperature across the interventions could have been due to a cold couch the subjects were lying on. This investigation includes limitations such as the small population size and a varied TENS neuro-sensitivity threshold. In conclusion, these findings provide a potential foundation for further research into the effects of tVNS and possible clinical applications.
| Original language | English |
|---|---|
| Number of pages | 1 |
| Publication status | Published - Jul 2024 |