Discovering the Vagus: Validation and Inter-Rater Reliability of the Vagus Nerve Neurodynamic Test Among Healthy Subjects

Abstract

Background: The Vagus Nerve (VN) neuropathies and autonomic peripheral neuropathies (APN) are responsible for neurodegenerative diseases and immune response alterations. Peripheral nerves selective tension tests (NDT) are clinical tools validated for neuropathies detection in lower and upper limbs. However, a validated NDT to assess VN is lacking. Methods: An estimated sample of 30 healthy subjects completed a questionnaire on vagal symptoms. The VN-NDT was administered, if neurological assessment of the cervical tract was negative. Symptoms and heart rate (HR) were monitored. The test validity was assessed using a motion capture analysis system and a real-time ultrasonography imaging (USI; C6-VN distance) during the test administrations. Inter-examiner accordance was tested (Cohen's Kappa) between two blinded assessors (one expert and one novice). Two-way analysis of variance (ANOVA) were performed with factors experience and side tested (2x2). A checklist with symptoms and signs of autonomic dysfunction was administered to all participants and accuracy, sensitivity, specificity, positive and negative likelihood ratios of the VN-NDT in autonomic dysfunction symptoms detection was calculated (ClinicalTrials.gov number, NCT04192877). The aim of the research was to define normtive data in order to establish a hallmark of physiological spectrum for pathology detection. Findings: The test induced a significant reduction of the C6-VN distance and of the HR (about 10 beats per minutes [bpm]; p< 0.01; d= .2; 95% confidence interval [CI]: 0.03–.3; p<0.001; d =.91; 95% CI: 0.63 – 1.03). Inter-examiner accordance was substantial and accuracy for gastrointestinal dysfunctions of the test was excellent (p<0.05; 95% CI:0.52–0.73; p<0.001; 95% CI:0.81–0.96). Interpretation: VN-NDT is a reliable and costless test that can be safely included in the bedside routine examination test. Reported normative data determine the hallmarks needed to screen clinical and preclinical conditions of Autonomic Peripheral Neuropathies (APN) and VN failures. Funding Statement: The authors stated: None. Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: The study was previously approved by the Bioethics Committee of the University of Turin (protocol 139870-14/03/2019).