Differences in Segmental β Response between Elastic and Muscular Arteries: A Comparison between Young and Adults

Introduction: The cardio-ankle vascular index (CAVI) is a noninvasive indicator used to assess arterial stiffness and predict atherosclerotic cardiovascular disease (ASCVD). CAVI represents a scale-converted form of the stiffness parameter β. Both CAVI and β reflect overall arterial stiffness from the heart to the ankle. However, there are distinct mechanistic pathways underlying the heterogeneous progression of ASCVD across the arterial tree (e.g., elastic and muscular arteries). Thus, the present study aimed to (1) examine differences in segmental β between elastic and muscular arteries at rest; (2) compare these differences between young and older adults at rest; and (3) further compare them with the segmental β responses observed after exercise. Methods: Eighty-three healthy individuals aged 18–52 years were recruited and divided into two groups: the young group (18–23 years, n = 57) and the adult group (31–52 years, n = 26). Cuffs were applied to both upper arms, the left thigh, and the right ankle. Segmental β was measured at rest as well as immediately after exercise using the Master’s two-step exercise test. Results: At rest, muscular arterial stiffness (thigh-ankle β [taβ]) was 4.7 times higher in the young group and 2.8 times higher in the adult group, compared to that of the elastic arteries (heart-thigh β [htβ]). htβ and heart-ankle β (haβ) were higher in the adult group than in the young group (p < 0.05), whereas taβ was lower in the adult group (p < 0.05). After exercise, taβ, htβ, and haβ decreased in both groups. In the young group, exercise-induced β reduction was greatest in taβ, compared with htβ and haβ. This reduction was significantly greater in the young group than in the adult group (e.g., reduction in taβ was 4.9 times greater in the young group). Conclusion: This study demonstrated distinct segmental β values between elastic and muscular arteries, suggesting that the inherent stiffness of the arterial beds should ideally be assessed separately.