Association between vagus nerve cross-sectional area measured by ultrasound and inflammatory biomarkers in hospitalised patients with COVID-19.

BACKGROUND: The vagus nerve plays an important role in neuroimmune communication. This study aimed to examine whether systemic inflammatory biomarkers are associated with ultrasound-measured cross-sectional area (CSA) of the vagus nerve in hospitalised patients with COVID-19. METHODS: In this cross-sectional study, 68 hospitalised adults with PCR-confirmed SARS-CoV-2 infection underwent bilateral ultrasound assessment of vagus nerve CSA. For each nerve, CSA was calculated as the mean of three measurements. Serum levels of C-reactive protein (CRP), fibrinogen, and ferritin were recorded. CSA values and inflammatory biomarkers were classified as within or outside predefined reference ranges. Binary logistic regression was used to assess associations between inflammatory biomarkers and vagus nerve CSA classified as outside the reference range. Receiver operating characteristic (ROC) analysis was performed. As a secondary exploratory analysis, a multilayer perceptron neural network was constructed to evaluate whether the same biomarkers could classify vagus nerve CSA as within or outside the reference range. RESULTS: Mean vagus nerve CSA was 1.32±0.30 mm2 on the right side and 1.20±0.28 mm2 on the left side. Inflammatory biomarkers were significantly associated with right vagus nerve CSA classified as outside the reference range in logistic regression, whereas no significant association was observed for the left vagus nerve. The regression model showed acceptable discriminative performance for the right vagus nerve (AUC=0.76, p=0.018). The exploratory neural network model showed similar classification performance. CONCLUSIONS: Systemic inflammatory biomarkers were associated with right vagus nerve CSA classified as outside the reference range on ultrasound, but not with left vagus nerve CSA, in hospitalised patients with COVID-19. These findings suggest a possible link between systemic inflammation and ultrasound-detectable variation in vagus nerve morphology. Larger studies are needed to confirm these findings and clarify their biological significance.