Effects of Vagus Nerve Stimulation on Central Pain Sensitivity & Parasympathetic Function in Knee Osteoarthritis

Investigating Effects of Auricular Vagus Nerve Stimulation on Central Pain Mechanisms, Autonomic Function, and Pain Severity in People With Knee Osteoarthritis

The goal of this clinical trial is to test the feasibility and effectiveness of transcutaneous vagus nerve stimulation (tVNS) to the ear on pain and autonomic function in people with knee osteoarthritis (OA). The main questions it aims to answer are: 1) whether tVNS is feasible to be used in people with knee OA; 2) whether tVNS demonstrates the trend in improving knee pain; and 3) whether tVNS has physiological effects on autonomic function (e.g., parasympathetic function) and pain perception in the central nervous system such as brain (i.e., central pain mechanisms). Participants will be asked to complete a battery of self-reported questionnaires about their demographic and behavioral information, ethnicity, pain, sleep, psychological/emotional symptoms. Subsequently, participants will complete baseline assessment where investigators will assess their knee pain severity, central pain sensitivity, and heart rate variability (a measurement for autonomic function). Then participants will receive a 60-minute tVNS. Investigators will redo the same assessment as baseline assessment after tVNS intervention to see the degree of knee pain, central pain sensitivity, and autonomic function changes. At the end of the study, investigators will assess their satisfaction level with the tVNS intervention and the feasibility of the intervention (e.g., completion rate, side effects).

Inclusion Criteria:

• chronic knee pain consistent with a clinical osteoarthritis diagnosis, which does not require radiographic evidence (age ≥ 45 years, activity-related knee pain, and no knee morning stiffness lasting >30 minutes)
• knee pain ≥ 3 months
• average pain intensity ≥ 4 on a scale from 0 to 10
• knee pain as the chief complaint
• able to understand English

Exclusion Criteria:

• current skin disease of the left ear interfering with the application of the auricular electrode for stimulation(eczema, urticarial lesion, skin infection, external otitis, etc.)
• auditory canal not adapted to the application of the ear electrode
• known history of cardiac rhythm disturbances or atrioventricular block > 1st degree, conduction disturbances
• recurrent vagal syncope
• history of vagotomy
• use of other medical devices electrically active (pacemaker, transcutaneous electrical nerve stimulation, etc)
• serious and uncontrolled concomitant disease, including cardiovascular, nervous system, pulmonary, renal, hepatic, endocrine, gastrointestinal, epileptic disease or malignant diseases
• pregnant or breastfeeding woman
• numbness or sensation loss on the body sites for pain measurements (i.e., the wrist, knee, the forearm)
• any intervention procedures for knee pain in the past 3 months
• age less than 45 years old