Ultrasound evaluation of vagus nerve cross-sectional area in a community-dwelling elderly Japanese cohort

Objectives Although the vagus nerve (VN) is easily observed by ultrasonography, few studies have evaluated the cross-sectional area (CSA) of the VN in healthy older individuals from East Asia. In this study, we aimed to report reference values for the CSA of the VN in community-dwelling elderly Japanese individuals and to identify any associated medical history and/or lifestyle factors. Methods The present study included 336 participants aged ≥ 65 years from a prospective cohort study conducted in Yahaba, Japan from October 2021 to February 2022. The CSA of the VN was measured bilaterally at the level of the thyroid gland by ultrasonography. Univariate and multivariable linear regression analyses were conducted to identify the associations between clinical and background factors and the CSA of the VN on each side. Results In our cohort, the median CSA of the VN was 1.3 mm 2 (interquartile range [IQR] 1.1– 1.6) on the right side and 1.2 mm 2 (IQR 1.0–1.4) on the left side. Multivariable linear regression analysis showed that history of head injury (β = -0.15, p < .01), history of convulsion (β = 0.19, p < .01), and BMI (β = 0.30, p < .01) were independently associated with the CSA of the VN on the left side. In contrast, there were no independent associations between any of the assessed variables and the CSA on the right side. Conclusion We have reported reference VN CSA values for community-dwelling elderly Japanese individuals. In addition, we showed that the CSA of the VN on the left side was positively associated with a history of convulsive seizure and BMI and inversely associated with a history of head injury.