Effects of Transcutaneous Vagus Nerve Stimulation in Parkinson´s Disease (tVNS_PD)

Effects of Transcutaneous Stimulation of the Auricular Branch of the Vagus Nerve in Parkinson´s Disease

This study aims to determine whether electrical stimulation of the ear, when combined with physical and speech therapy, can improve symptoms in subjects diagnosed with Parkinson´s disease, by comparing two different application sites.

Each subject will undergo an initial in-person screening and provide consent before participating in the study.

The main questions to answer are:

• Does transcutaneous electrical nerve stimulation (tVNS) in the ear paired with physical and speech therapy improve speech and voice-related problems, airway protection, salivation, and swallowing?
• Does tVNS paired with physical and speech therapy improve tremor, walking speed, and balance in people with PD?
• Does tVNS paired with physical and speech therapy improve heart rate and heart rate variability in people with PD?
• Do its effects persist at 8 weeks?

Participants will:

Attend 12 rehabilitation sessions over 4 weeks (three per week). During each session, participants received either active or sham tVNS, accompanied by speech therapy (once per week), physical therapy (once per week), or conducted alone (once per week).

Undergo speech, voice, swallowing, respiratory, gait, balance, tremor, heart rate variability, and cognitive testing, as well as questionnaires regarding the quality of life, before and after treatment.

Return for a follow-up visit eight weeks after therapy to check how long the effects last.

Study Overview

• Status: Recruiting
• Conditions: Parkinson Disease (PD); Transcutaneous Vagal Nerve Stimulation (tVNS)
• Intervention / Treatment: Device: Transcutaneous Electrical Nerve Stimulation (TENS) of Vagus Nerve; Other: Conventional Physical therapy; Other: Conventional Speech Therapy; Device: Sham Transcutaneous Electrical Stimulation of Vagus Nerve

Detailed Description

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. Most people with PD will experience dysfunction of the autonomic nervous system (ANS), although the severity of this dysfunction can vary widely, affecting both physical and mental well-being. Symptoms are typically classified as motor or non-motor. Prominent motor symptoms of PD include bradykinesia, rigidity, tremor, and abnormalities in gait, balance, and posture. These symptoms are associated with falls and have a very negative impact on quality of life. In addition, impaired fine motor skills, combined with respiratory and other problems, significantly affect voice, speech, and swallowing, as well as other non-motor disorders, such as neuropsychiatric, sleep, sensory, and digestive disorders.

This study is a double-blind, randomized, controlled trial designed to evaluate the efficacy of transcutaneous auricular vagus nerve stimulation on the motor and non-motor effects of Parkinson´s Disease (PD). Investigators will recruit up to 46 patients. The volunteers will be randomized by sex and the Hoehn and Yahr stage. Clinical information and, specifically, Unified Parkinson's Disease Rating Scale (UPDRS) -III (section III) will be assessed initially.

The primary variable of the study will be voice variables, such as volume, jitter, and shimmer. The remaining dependent variables will be other voice and acustic measures; the presence and severity of dysphagia; the presence and severity of xerostomia and sialorrhea; swallowing efficiency, peak cough flow; the level of tremor; the severity of gait dysfunction; balance; cognitive ability regarding concentration and response inhibition; heart rate and heart rate variability; quality of life in PD; adverse effects; and the degree of effectiveness of blinding.

Over the course of 4 weeks, participants will receive 30-minute stimulation sessions three times weekly, along with physiotherapy and speech therapy once per week. One group will be assigned to stimulation in the cymba concha (where the vagus nerve is placed) and the other (sham) in the earlobe.

Data collection will occur at baseline (T0), post-intervention (T1- 4 weeks), and 8 weeks after finishing the intervention (T2), except for the intensity required to administer electrical stimulation and adverse effects, which will be studied during the whole intervention. Tolerance will be assessed on day 1 of stimulation and on day 12 (4 weeks). Statistical analyses will employ mixed-model approaches to evaluate changes in outcome measures over time and between interventions.

• Study Type: Interventional
• Enrollment (Estimated): 46
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Alicia Martínez-Rodríguez alicia.martinez@udc.es, Lecturer; Phone Number: +34 881015851; Email: alicia.martinez@udc.es
• Study Contact Backup: Name: Olalla Bello, Lecturer; Phone Number: +34 881015852; Email: olalla.bello@udc.es

Study Locations

• Spain
  • A Coruña, Spain, 15008
    • Recruiting
    • Association of Parkinson´s Disease Galicia- Coruña
    • Contact: Alba Gómez-Rodríguez; Phone Number: +34 618950128; Email: logopedia3@parkinsongaliciacoruna.org
    • Sub-Investigator: Alba Gómez-Rodríguez, Ph.D. student
    • Sub-Investigator: María Belén López-Ferreiro
    • Sub-Investigator: Sandra García González
    • Sub-Investigator: María Rodríguez Losada

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child; Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Being a member of the Association or be interested in joining;
• Idiopathic PD diagnosis, stages 2-3 according to the Hoehn & Yahr scale; confirmed by neurologist
• Ability to walk independently for at least 1 minute ant turn 180° without assistance;
• Exhibiting symptoms of hypokinetic dysarthria;
• On stable dopaminergic therapy for at least 1 month prior to the experiment

Exclusion Criteria:

• Any contraindication for taVNS (e.g., ear lesions, pacemakers, defibrillators, or other electronic devices)
• Previous vagotomy or previous application of electrical stimulation to the ear or brain, or treatment with high-intensity focused ultrasound (HIFU)
• Voice or speech disorders caused by other medical conditions
• MoCA score below 21
• Psychotic symptoms or hallucinations; a diagnosis of psychiatric illness
• Systolic blood pressure above 160 mm Hg, and diastolic blood pressure above 100 mm Hg
• Inability to attend sessions;
• Concomitant neurological, orthopaedic, cardiac, respiratory or active medical/oncological condition that would affect participation

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Double

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Active tVNS paired with conventional Speech Therapy and Physical Therapy; Participants in this arm will receive transcutaneous electrical stimulation applied to the concha of the left ear for 30 minutes, three times a week, over a 4-week period. This location is known to be innervated by the auricular branch of the vagus nerve. In addition, a speech therapy session and a physical therapy session will be added once a week each, while receiving the electrical stimulation.	Device: Transcutaneous Electrical Nerve Stimulation (TENS) of Vagus Nerve; The tVNS will be performed at 200 microseconds, with frequencies ranging from 20 to 200 Hz (30 seconds/30 seconds) for 30 minutes, in the area innervated by the auricular branch of the vagus nerve (cymba concha and concha). The individually titrated intensity will be set above the sensory threshold (intense tingling sensation) but below the level of discomfort.; Other Names: taVNS; tVNS; transcutaneous auricular vagus nerve stimulation; Other: Conventional Physical therapy; Physical therapy delivered to both groups consists of exercises aimed at posture alignment and body coordination, static and dynamic balance improvement, and gait quality. It will be delivered once a week, during a session of electrical stimulation.; Other: Conventional Speech Therapy; It will focus on the orofacial muscles, the acquisition of a diaphragmatic-abdominal breathing pattern that integrates breathing with vocal production, voice training with exercises that enhance vocal quality and prosody, articulation exercises to improve speech clarity, and swallowing training. It will be administered once a week, during one of the three electrical stimulation sessions.
Sham Comparator: Sham tVNS paired with Speech Therapy and Physical Therapy; Participants in this arm will receive the same transcutaneous electrical stimulation as the active group, but applied to the earlobe, a site not innervated by the vagus nerve. The procedure, the appearance of the device, and the parameters are identical to those of the active condition to maintain participant blinding. In addition, a speech therapy session and a physical therapy session will be added once a week each, while receiving the electrical stimulation.	Other: Conventional Physical therapy; Physical therapy delivered to both groups consists of exercises aimed at posture alignment and body coordination, static and dynamic balance improvement, and gait quality. It will be delivered once a week, during a session of electrical stimulation.; Other: Conventional Speech Therapy; It will focus on the orofacial muscles, the acquisition of a diaphragmatic-abdominal breathing pattern that integrates breathing with vocal production, voice training with exercises that enhance vocal quality and prosody, articulation exercises to improve speech clarity, and swallowing training. It will be administered once a week, during one of the three electrical stimulation sessions.; Device: Sham Transcutaneous Electrical Stimulation of Vagus Nerve; The sham- tVNS will be performed at 200 microseconds, with frequencies ranging from 20 to 200 Hz (30 seconds/30 seconds) for 30 minutes, with electrodes placed on the earlobe, which lacks vagus nerve innervation. The individually titrated intensity will be set above the sensory threshold (intense tingling sensation) but below the level of discomfort.; Other Names: Sham location; sham-tVNS; sham- taVNS; sham transcutaneous vagus nerve stimulation

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Voice intensity	The PRAAT software will be used to test the voice twice, when sustaining till 10 seconds the vowel "a" and when reading a text at their usual volume. The intensity (voice volume, measured in decibels) will be recorded.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Voice- Jitter	It is derived from the sustaining till 10 seconds the vowel "a". Then, PRAAT software will be used to test the voice, discarding the beginning and the end. The Jitter is defined as the variation in frequency from cycle to cycle, a measure of vocal instability, expressed as a percentage. The higher the percentage, the more irregularities the voice will have.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Voice- Shimmer	It is derived from the sustaining till 10 seconds the vowel "a". Then, PRAAT software will be used to test the voice, discarding the beginning and the end. The Shimmer refers to the variation in the amplitude of the sound wave. It is a measure of vocal instability, expressed as a percentage. The higher the percentage, the more irregularities the voice will have.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Voice fundamental frequency (F0)	The PRAAT software will be used to test the voice twice, when sustaining till 10 seconds the vowel "a" and when reading a text at their usual volume. The fundamental frequency (F0) is the oscillation originating from the vocal folds. It will be recorded in Hz.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Harmonic to Noise Ratio (HNR)	The PRAAT software will be used to test the voice twice, when sustaining till 10 seconds the vowel "a" and when reading a text at their usual volume. The Harmonic to Noise Ratio (HNR), a measure of the ratio between the periodic and non-periodic components that make up a segment of spoken voice, will be recorded. This ratio reflects the efficiency of sound production; that is, the greater the amount of airflow converted from the lungs into vocal cord vibration energy, the higher the HNR will be. A low HNR indicates a weak voice and dysphonia.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Maximum phonation time (MPT)	The participant will be asked to sustain the vowel /a/ for as long as possible after a deep inhalation. It will be repeated three times, and the best value will be recorded. The maximum phonation time (MPT) will be measured in seconds. The same procedure will be taken for the /s/.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Maximum expiratory time during sustained /s/	The participant will be asked to sustain the /s/ sound for as long as possible after a deep inhalation. It will be repeated three times, and the best value in seconds will be recorded.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Index s/a	The index s/a is used to compare respiratory with laryngeal function, based on the assumption that the two are similar, so the ratio should be 1.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Diadihokinetic rates (DDK)	Diadochokinesis measures the ability to perform rapid, alternating muscle movements in a repetitive manner. It assesses the rate and regularity of consonant-vowel repetitions /pa-ta-ka/. The individual is instructed to repeat the syllables /pa-ta-ka/ as quickly and accurately as possible for 10 seconds. The higher the value, the better.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Self-perceived handicap associated with dysphonia: Voice Handicap Index (VHI-10)	The Voice Handicap Index- 10 (VHI-10) is a valid instrument for assessing self-perceived disability associated with dysphonia. It consists of 10 items designed to evaluate patients´ perception of the impact of voice disorders on their quality of life. Each item contains specific questions related to the functional, emotional, and physical aspects of the voice. The patient must answer on a Likert-type scale with options ranging from 0 (never) to 4 (always). The total score is obtained by summing the responses, with a range of 0 to 40, where higher scores indicate a greater degree of vocal impairment.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Salivation	To measure salivation, a dry cloth will be placed in the mouth and weighed after 2 minutes without swallowing to estimate the volume of saliva produced. Changes in weight will be recorded. A higher final weight-and thus a greater difference-indicates increased saliva production.	Baseline (T0), post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Swallowing- dysphagia	It will be measured by Repetitive Saliva Swallowing Test (RSST), where the patient is asked to swallow saliva as many times as possible for 30 s, while deglutition is counted through palpation of the larynx. A value below 3 swallows has been found to be pathological.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Cookie Swallow Test	Time will be measured (velocity), swallow security and efficacy, checking for any residue after swallowing.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Timed Water Swallow Test (TWST)	The time taken to consume 150 mL of bottled water and the swallowing capacity (mL/s) will be measured, as well as efficacy and safety. We will assess whether there has been a reduction in swallowing time, indicating an improvement in swallowing ability.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Sialorrhea	The Sialorrhea Clinical Scale for Parkinson´s Disease assesses sialorrhea; drooling severity, drooling frequency and impact on daily life,. It is a Likert-type 7-item. Each item is ranked on a scale of 0 to 3, with a maximum score of 21. Higher scores correspond to greater disability.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Cough Peak Flow (CPF)	It measures the maximum amount of air exhaled by coughing after taking a deep breath, using the best of three attempts. The A CPF above 270 L/min is associated with an effective cough and good ability to expel secretions. In contrast, a CPF below 160 L/min is considered an ineffective cough, with a higher likelihood of respiratory complications.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow
Cognitive ability to concentrate and inhibit responses- Flanker test	The Flanker test is designed to assess selective attention and inhibitory function, indicating the direction of a central row, flanked by non-target stimuli, which can be congruent (matching the target) or incongruent (opposite to the target). It will be done using an app (C2 Flanker Task) on a tablet with both thumbs at the same time. The reaction time is measured, with higher times indicating less ability to suppress responses to distracting stimuli while focusing on a target stimulus.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Hand tremor	The tremor in left hand will be measured with the app (G-Sensor Logger) for a minute, using a mobile phone secured to the hand.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Static balance- distances	For static balance, a baropodometric platform will be used, and the centre of pressure area (mm), the ellipse area (mm2), and the displacements in the axes of space (mm) will be measured, with eyes open, twice.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Static balance- velocity	For static balance, a baropodometric platform will be used, and the speed (mm/s) of displacements along the axes of space will be measured, with eyes open, twice.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Dynamic balance and functional mobility	The Timed Up and Go test (TUG) represents a measure of global ambulation skills. The patient sits back in a standard chair and, on the command "go", the patient rises, walks 3 meters at a comfortable and safe pace, turns, walks back to the chair and sits down. Time for each attempt is recorded. The best result from 3 attempts will be selected. The longer it takes to complete, the worse the situation becomes, with 12 seconds being the cutoff point for the risk of falling.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Heart Rate Variability (HRV)- frequency domain	Heart Rate Variability (HRV) using Kubios app and H10 polar heart rate monitor chest strap in periods of 5 minutes: Frequency domain; ratio LF/HF power will be calculated along with normalised LF/HF where baseline values will set to 1; Low frequency (LF, referred to HRV frequency band 0.04-0.15 Hz); High frequency (HF = HRV frequency band 0.15-0.4 Hz); absolute powers of LF, and HF bands (ms2); normalized power (powers of LF and HF bands in normalised units, %)	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Heart Rate Variability (HRV)- time domain	Heart Rate Variability (HRV) using Kubios app and H10 polar heart rate monitor chest strap in periods of 5 minutes: Time domain: RR (mean values of RR intervals in ms) ; SDNN (Standard deviation of RR intervals); RMSSD (Root mean square of successive RR interval differences, in ms)	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Heart Rate Variability (HRV)- Global measures	Heart Rate Variability (HRV) using Kubios app and H10 polar heart rate monitor chest strap in periods of 5 minutes: Global measures: Stress Index (SI), square root of Baevsky's stress index; Parasympathetic nervous system (PNS) index; Sympathetic nervous system (SNS) index	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Quality of life in Parkinson´s Disease (PDQ-8)	Quality of life will be assessed using the Parkinson's Disease Questionnaire-8 (PDQ-8), which measures mobility, activities of daily living, emotional well-being, stigma, social support, cognition, communication, and bodily discomfort. Each item is scored on a 0 (= never) to 4 (= always or cannot do at all) range, so the lowest and highest possible scores are 0 and 32, respectively. Greater scores indicate poorer quality of life.	Baseline (T0), Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Effectiveness of blinding	Participants will be asked what stimulation they think they have just received, active or placebo (or what is their best guess) and why. Comparison of participants´perceptions with the actual assignment, James Bang Index.	Post-intervention (T1, 4 weeks), along with an 8-week post-trial follow-up (T2)
Adverse effects	A questionnaire will be used to test the presence, severity, persistence and causality of ear pain, headache, tingling, itching, redness, irritation, pressure, dizziness, nausea, vertigo, fatigue, vertigo, palpitations, tinnitus, unpleasant feeling, and/or other effects.	All days of intervention (up to 4 weeks)
Tolerance to auricular TENS	The level of tolerance of the entire stimulation (by electrical stimulation, by electrodes, or by both) will be measured on a VAS scale from 0 (no discomfort at all) to 10 (the discomfort would have prevented me from finishing the session).	Baseline and week-4
Amplitude of electrical stimulation	Amplitude used in the auricular electrical stimulation in mA, as well as the sensory and discomfort threshold.	All days of intervention (up to 4 weeks)

Collaborators and Investigators

• Sponsor: Universidade da Coruña
• Collaborators: Parkinson´s Association Galicia-Coruña
• Investigators: Principal Investigator: Alicia Martínez-Rodríguez, Lecrurer, Universidade da Coruña; Principal Investigator: Olalla Bello, Lecurer, Universidade da Coruña

Study record dates

Study Major Dates

• Study Start (Estimated): May 1, 2026
• Primary Completion (Estimated): September 1, 2026
• Study Completion (Estimated): November 1, 2026

Study Registration Dates

• First Submitted: April 23, 2026
• First Submitted That Met QC Criteria: May 11, 2026
• First Posted (Actual): May 14, 2026

Study Record Updates

• Last Update Posted (Actual): May 19, 2026
• Last Update Submitted That Met QC Criteria: May 15, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Quality of Life; Gait; cognition; Posture; Deglutition; Parkinson Disease; Xerostomia; cough; Physical Therapy Modalities; Tremor; Heart Rate; Sialorrhea; transcutaneous electrical nerve stimulation; voice disorders; Vagus Nerve; Speech Therapy; Ear
• Additional Relevant MeSH Terms: Synucleinopathies; Neurologic Manifestations; Mouth Diseases; Stomatognathic Diseases; Brain Diseases; Central Nervous System Diseases; Nervous System Diseases; Mental Disorders; Respiratory Tract Diseases; Neurobehavioral Manifestations; Respiration Disorders; Neurodegenerative Diseases; Otorhinolaryngologic Diseases; Signs and Symptoms, Respiratory; Neurodevelopmental Disorders; Movement Disorders; Salivary Gland Diseases; Parkinsonian Disorders; Basal Ganglia Diseases; Dyskinesias; Laryngeal Diseases; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Parkinson Disease; Communication Disorders; Cough; Tremor; Voice Disorders; Xerostomia; Sialorrhea; Therapeutics; Physical Therapy Modalities; Rehabilitation; Anesthesia and Analgesia; Electric Stimulation Therapy; Analgesia; Transcutaneous Electric Nerve Stimulation
• Other Study ID Numbers: 2025/295_II

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: The IPD that underlie the results included in the publication will be shared on Zenodo, with a description of the codes and the information needed to understand them.
• IPD Sharing Time Frame: Beginning 1 year after publication and with no ending while Zenodo keep the data
• IPD Sharing Access Criteria: The results will be included in a document that will be shared on Zenodo with all investigators interested in them via direct access.
• IPD Sharing Supporting Information Type: SAP

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No