Effect of transcutaneous vagal nerve stimulation on heart rate variability in recovery phase following Stroop test

Daisuke Fujita, Tsubasa Mitsutake, Kotarou Kawashima, Tatsuya Tagawa
Purpose:

The present study was designed to investigate the effect of tVNS on heart rate variability (HRV) after mental stress using the Stroop test.

Methods:

Participants were 14 healthy adult males randomly assigned to tVNS group (n = 7) and sham group (n = 7). The measurement protocol consisted of 5 minutes of rest, 20 minutes of Stroop test, and 10 minutes of stimulation of tVNS or sham. The Stroop test was answered every second using a personal computer. For tVNS, electrodes were placed on the left auricle and the stimulus intensity was set between sensory and pain thresholds. Stimulation frequency was set at 25 Hz and On-Off time was 30 s. Sham stimulation was performed with an electrode attached to the auricle and a similar tVNS protocol. ECG data were recorded on a personal computer at CM5 inductions. RR intervals were analyzed by frequency, and total power (TP), very low frequency component (VLF), low frequency component (LF), high frequency component (HF), and LF/HF of the HRV were log-transformed values.  Statistical analysis was performed by two-way analysis of variance on the HRV during the Stroop test and stimulation. When no interaction was found, a corresponding t-test was used to examine the modulation of HRV by stimulation after the Stroop test.

Results:

There were no interactions between each HRV analysis. Interstimulus examination revealed significant increases in TP, VLF, and LF in both groups during stimulation period. HF component unchanged significantly in the tVNS group but did increase significantly in the sham group.

Conclusion(s):

The results of this study indicate that tVNS may inhibit the variability of the HF component after the Stroop test. Although, the pattern of HRV after cognitive stress is not uniform and may be influenced by individual differences. Therefore, application of tVNS after mental stress would require a stimulation protocol that accounts for individual variability. 

Implications:

The results of this study suggest that modulation of vagal activity by tVNS may affect the recovery process of vagal activity after mental stress. Thus, the physiological effects of tVNS on mental stress may not be assessed by HRV. 

Funding acknowledgements:
This research was supported by Fukuoka International University of Health and Welfare.
Keywords:
transcutaneous vagal nerve stimulation
heart rate variability
Stroop test
Primary topic:
Mental health
Second topic:
Cardiorespiratory
Did this work require ethics approval?:
Yes
Name the institution and ethics committee that approved your work:
The Ethics Review Board of FUKUOKA INTERNATIONAL UNIVERSITY OF HEALTH AND WELFARE
Provide the ethics approval number:
22-FIUHW-017
Has any of this material been/due to be published or presented at another national or international conference prior to the World Physiotherapy Congress 2025?:
No

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