Effects of Transcutaneous Auricular Vagus Nerve Stimulation on Perceived Stress and Psychological Distress in University Students With High Distress Levels: A Randomized Blinded Clinical Trial
Phase: NA
Conditions: Psychological Distress, Stress (Psychology), Perceived Stress
Sponsor: Egas Moniz - Cooperativa de Ensino Superior, CRL

Cover Page 
OƯicial Study Title 
Impact of taVNS on Stress Levels in University Students 
 
ClinicalTrials.gov Identiﬁer (NCT Number) 
NCT07411846 
 
Unique Protocol ID 
 PT-280/24 
 
Document Type 
Study Protocol / Clinical Study Documentation 
 
Document Date 
18 November 2024 
 
Conﬁdentiality Statement 
This document contains proprietary and conﬁdential information intended solely for 
regulatory review, ethics committee submission, or authorized study personnel. 
Unauthorized distribution or reproduction is prohibited. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Methods 
 
Study design 
 
This study will be a blinded, randomized, sham-controlled trial using a convenience sample 
of university students from the Egas Moniz School of Health and Science. Assessments will 
be conducted at three time points: pre-intervention (baseline), immediately post-
intervention, and 1-month follow-up. The study will be designed to evaluate feasibility and 
tolerability as primary objectives, with preliminary efficacy estimates as secondary 
objectives. 
 
Participants 
 
Eligibility criteria will include: (a) being enrolled as a university student, (b) age ≥ 18 years, 
and (c) high to very high psychological distress (K-10 ≥ 22). 
 
Exclusion criteria will be: initiation or dose change of psychotropic medication within the 
prior 3 months, substance dependence, ongoing psychological or psychotherapeutic 
treatment, self-reported formal mental disorder diagnosis (collected via participant self-
report without formal diagnostic verification), or contraindications for taVNS (e.g., 
pregnancy, history of dizziness or seizures, cochlear implants, ear plastic surgery, or 
auricular malformations). 
 
The final sample will comprise 40 participants, equally distributed across groups (taVNS: n 
= 20; sham: n = 20). 
Sample size justification 
 
This randomized trial will be primarily designed as a feasibility and tolerability study. No a 
priori power calculation will be conducted; the target sample size of 40 participants (20 per 
group) will be determined pragmatically based on logistical constraints and the aim of 
obtaining preliminary estimates of outcome variability and change over time. 
 
Given the small sample and very small anticipated time×group effect, the study will not be 
powered to detect small between-condition differences and should be interpreted 
primarily in terms of feasibility, tolerability, and overall within-subject improvements. 

Measures 
 
Perceived stress. Perceived stress will be assessed using the 10-item Perceived Stress 
Scale (PSS-10 (Cohen et al., 1983)), scored from 0 ("never") to 4 ("very often"), summed to 
a total score ranging from 0 to 40, with higher scores reflecting higher perceived stress. 
Internal consistency (Cronbach's alpha) in this study will be 0.76 (pre-intervention), 0.83 
(post-intervention), and 0.89 (follow-up). 
 
Psychological distress. Psychological distress will be assessed using the 10-item Kessler 
Psychological Distress Scale (K-10 (KESSLER et al., 2002; Pereira et al., 2019)), scored from 
1 ("never") to 5 ("always") in reference to the preceding 30 days, summed to a total score 
ranging from 10 to 50, with higher scores reflecting greater distress. A score of ≥ 22 will 
indicate high to very high distress. Internal consistency (Cronbach's alpha) in this study will 
be 0.81 (pre-intervention), 0.87 (post-intervention), and 0.91 (follow-up). 
 
Sociodemographic and clinical screening. A sociodemographic questionnaire will be 
used to characterize the sample (age and sex) and to gather clinical information relevant to 
exclusion criteria (including medical comorbidities, psychotropic medication use, 
participation in psychotherapeutic groups, and self-reported mental disorder diagnosis). 
 
Procedures 
 
Recruitment will take place via brief in-person classroom information sessions, after which 
interested students will access an online link to enroll. Following the provision of informed 
consent, candidates will complete a baseline assessment (sociodemographic 
questionnaire, PSS-10, and K-10). Eligible participants will be contacted by email to 
schedule sessions. 
 
Participants will be randomly allocated (1:1) to taVNS or sham stimulation using an online 
research randomizer (https://www.randomizer.org/) following eligibility confirmation. 
Allocation will be concealed from participants until debriefing. Participants will be 
informed that they will be assigned to one of two stimulation protocols differing in electrode 
placement; they will not be informed of the existence of a sham condition, and this 
information will only be provided after completion of the 1-month follow-up assessment 
(debriefing). 

 
All stimulation sessions will be conducted in a university laboratory, delivered by trained 
study personnel. Personnel will be aware of electrode placement (tragus vs. earlobe) but 
will be blinded to the interpretation of placement as "active" versus "sham." 
 
Immediately before the first session, exclusion criteria will be re-checked; no participant 
will be expected to meet exclusion criteria at that time. 
 
The intervention will comprise five consecutive daily sessions of 30 minutes each, delivered 
using the Parasym® Device (Parasym Health Inc., London, UK) with a preset pulse width of 
250 µs and frequency of 20 Hz. Stimulation intensity will be individually titrated at the start 
of each session to a "comfortable but noticeable" sensory level and adjusted as needed 
across sessions to maintain this level. The sole procedural difference between groups will 
be electrode placement: in the taVNS group the electrode will be positioned on the left 
tragus, whereas in the sham group it will be positioned on the left earlobe. 
 
Following the fifth session, participants will complete post-intervention questionnaires 
(PSS-10 and K-10) and will be contacted by email 1 month later to complete the follow-up 
assessment. 
 
Upon study completion and debriefing, sham participants will be offered stimulation with 
electrode placement on the tragus; none will have accepted at the time of writing. 
 
Adverse events will be monitored before and after each session through open-ended 
questioning and observation. No clinically significant adverse reactions will be recorded 
beyond transient mild redness at the stimulation site in some participants, and no 
participant will report stimulation-related side effects during or after taVNS sessions. 
 
Statistical analysis 
 
Analyses will be performed using IBM SPSS Statistics version 30. Descriptive statistics 
(means, standard deviations, frequencies) will characterize the sample and outcomes. 
Internal consistency will be assessed using Cronbach's alpha. 
 

Primary analyses will test changes over time and group differences using a repeated-
measures MANOVA with time (pre-intervention, post-intervention, follow-up) as the within-
subject factor and group (taVNS vs. sham) as the between-subject factor, using two 
correlated dependent variables (PSS-10 and K-10). This will be followed by univariate 
repeated-measures ANOVAs (one per outcome) and Bonferroni-corrected pairwise 
comparisons across time points. 
 
Assumptions will be tested prior to analysis. Sphericity will be evaluated using Mauchly's 
test, and multivariate normality will be assessed using Box's M test. When Box's M is 
significant, Pillai's trace will be used as a robust multivariate test statistic. 
 
All randomized participants will be included in the analysis, and there will be no missing 
data. Alpha will be set at .05 (two-tailed) for all tests. 
 
 

 
Informed Consent 
Código| IMP-EM-PE-17_03 
 
____________,___________________________________. 
                         (Place) (DD Month YYYY 
 
 
Dear Sir/Madam, 
Within the scope of the project “EƯects of transcranial direct current electrical stimulation 
of the right and left dorsolateral prefrontal cortex or non-invasive vagus nerve stimulation 
in adult individuals with chronic stress”, developed at the Laboratory of Functional 
Physical Assessment in Physiotherapy (LAFFFi) at Egas Moniz, under the supervision of 
Professor Dr. Luciano Maia Alves Ferreira, your participation is kindly requested. 
 
The aim of the study is to investigate the eƯects of transcranial direct current electrical 
stimulation and non-invasive vagus nerve stimulation in adults with chronic stress. 
Participation involves completing ﬁve questionnaires assessing symptoms, 
psychological distress and stress scales, sleep quality, and demographic data, taking 
approximately 25 minutes (to be ﬁlled in before, after, and one month after the 
interventions). You will also take part in the non-invasive neuromodulation protocol, 
consisting of cranial or auricular electrical stimulation, which is indicated for the 
treatment of chronic stress. The intervention will comprise ﬁve sessions of 20 minutes 
each, carried out over the course of one week and supervised by an experienced 
professional. 
 
During the study, minimal risks may occur, such as embarrassment, mild discomfort, or 
lack of time to complete the questionnaires during the ﬁrst and last sessions. During or 
after treatment, you may experience mild side eƯects (such as drowsiness, pain, itching, 
or tingling sensations in the stimulated area). It is important to emphasize that these 
reactions are rare, mild, and limited to the stimulation period. 
 
Participation in this study is voluntary. Choosing not to participate will not result in any 
disadvantage or penalty. 

This study may oƯer potential beneﬁts, including the possibility of non-pharmacological 
treatment, reduction of stress symptoms, and improvement in sleep quality. 
The data collected will be used exclusively for statistical analysis and/or publication 
purposes, and will be processed by the supervisor(s) and/or their authorized 
representatives. All data will be handled anonymously and conﬁdentially. 
(Strike out what does not apply) 
I AGREE / DO NOT AGREE to participate in this study, conﬁrming that I have been fully 
informed about the study’s conditions and have no further questions. 
 
(Signature of the participant or, in the case of minors, of the parent/guardian)