Effects of Transcutaneous Auricular Vagus Nerve Stimulation on Fatigue in Post-COVID Syndrome: A Randomized, Single-Blind, Sham-Controlled Study

Background:Post-COVID syndrome (PCS) is a condition that occurs after COVID-19 infection that lasts for more than three months and adversely affects the autonomic nervous system (ANS). The aim of this study was to investigate and compare the effectiveness of transcutaneous auricular vagus nerve stimulation (taVNS) and sham taVNS in fatigue in individuals with PCS.
Methods:Forty-two patients (20 male, 22 female) with PCS participated in this study. The severity of fatigue was assessed with the fatigue severity scale (FSS). Heart rate variability (HRV) was measured in participants at baseline and after taVNS. The participants were randomly divided into two groups (taVNS and sham taVNS). taVNS was applied for 20 consecutive days for 30 min each (10 Hz, 300 μs).
Results:The groups were similar in FSS and HRV at baseline (p > 0.05). After the intervention, FSS decreased in taVNS (p = 0.018) and sham taVNS (p = 0.036). RMSSD increased in taVNS (p = 0.010), with no change in sham taVNS (p > 0.05) from baseline to after treatment. Stress index showed no change in both groups (p > 0.05). PNS index increased in taVNS (p = 0.007) and sham taVNS (p = 0.049). The SNS index and low frequency (LF) power decreased in taVNS (p = 0.001, p = 0.017, respectively), with no change in sham taVNS (p > 0.05). High frequency (HF) power showed no change within groups (p > 0.05). LF/HF decreased in taVNS (p = 0.002), with no change in sham taVNS (p > 0.05). Pre- and Post-tests showed taVNS was more effective than sham taVNS in decreasing FSS (p = 0.022) and LF power (p = 0.029), in increasing PNS index (p = 0.016). There was a difference in HF power between groups after treatment (p = 0.042).
Conclusion:Both taVNS and sham taVNS were effective in reducing the severity of fatigue, with sham taVNS being superior to taVNS. The observed effect size was smaller than anticipated. This suggests that larger-sample-size studies are required to verify these results.

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