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. 2023 Sep;48(3):323-333.
doi: 10.1007/s10484-023-09584-4. Epub 2023 Mar 15.

Expiratory-gated Transcutaneous Auricular Vagus Nerve Stimulation (taVNS) does not Further Augment Heart Rate Variability During Slow Breathing at 0.1 Hz

Mikołaj Tytus Szulczewski  1 , Martina D'Agostini  2 , Ilse Van Diest  2
Affiliations

Expiratory-gated Transcutaneous Auricular Vagus Nerve Stimulation (taVNS) does not Further Augment Heart Rate Variability During Slow Breathing at 0.1 Hz

Mikołaj Tytus Szulczewski et al. Appl Psychophysiol Biofeedback. 2023 Sep.

Abstract

As cardiac vagal control is a hallmark of good health and self-regulatory capacity, researchers are seeking ways to increase vagally mediated heart rate variability (vmHRV) in an accessible and non-invasive way. Findings with transcutaneous auricular vagus nerve stimulation (taVNS) have been disappointing in this respect, as its effects on vmHRV are inconsistent at best. It has been speculated that combining taVNS with other established ways to increase vmHRV may produce synergistic effects. To test this idea, the present study combined taVNS with slow breathing in a cross-over design. A total of 22 participants took part in two sessions of breathing at 6 breaths/min: once combined with taVNS, and once combined with sham stimulation. Electrical stimulation (100 Hz, 400 µs) was applied during expiration, either to the tragus and cavum conchae (taVNS) or to the earlobe (sham). ECG was recorded during baseline, 20-minutes of stimulation, and the recovery period. Frequentist and Bayesian analyses showed no effect of taVNS (in comparison to sham stimulation) on the root mean square of successive differences between normal heartbeats, mean inter-beat interval, or spectral power of heart rate variability at a breathing frequency of 0.1 Hz. These findings suggest that expiratory-gated taVNS combined with the stimulation parameters examined here does not produce acute effects on vmHRV during slow breathing.

Keywords: Breathing at 0.1 Hz; Heart rate variability (HRV); Slow breathing; Transcutaneous auricular vagus nerve stimulation (taVNS).

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Conflict of interest statement

The authors declares that the authors have no conflict of interest.

Figures

Fig. 1
Fig. 1
Study design (upper panel) and structure of one laboratory session (lower panel). The laboratory sessions differed only in the use of taVNS or sham stimulation
Fig. 2
Fig. 2
Location and shape of electrodes indicated by a gray rectangle and circle (dashed line indicates the placement of the electrode on the inside of the tragus)
Fig. 3
Fig. 3
The synchronization of taVNS with the breathing phase and time of off (inspiration)/on (expiration) phases. The figure also displays the gradual increase and decrease of stimulation intensity during the first and last seconds of taVNS.
Fig. 4
Fig. 4
Mean respiratory rate, root-mean-square of successive differences (rMSSD), and interbeat interval (IBI) for the three timepoints of the study and both conditions (separate lines), along with 95% confidence intervals. Asterisks indicate the significance of the effect of the phase of the study (baseline, stimulation, and recovery). All interactions between phase and condition were non-significant
See this image and copyright information in PMC

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