Relation of carotid-to-femoral pulse wave velocity to aortic stiffness and total arterial compliance in healthy individuals

Background: Carotid-to-femoral pulse wave velocity (c-f PWV) is commonly used to assess large artery stiffness, particularly as a surrogate of aortic stiffness. Given that c-f PWV represents the average stiffness of all main arteries along the carotid-to-femoral arterial pathway, without specifically accounting for the stiffness of the proximal aorta, we hypothesized that c-f PWV may not represent stricto sensu the stiffness of the ascending aorta (AAO), which is the main contributor to total arterial compliance ( C T ). Methods: To test our hypothesis, we recruited 45 healthy volunteers from different age groups. We evaluated the relation between c-f PWV and different indices of proximal aorta stiffness calculated from distensibility (AAO dist PWV) and characteristic impedance ( Z c ) in frequency (AAO Zc(f) PWV) and time domain (AAO Zc(t) PWV) and compared their relationships with age and C T . 2D phase contrast MRI was performed to measure AAO flow and cross-sectional area. Tonometry was used to obtain c-f PWV and pressure waveforms. Results: In healthy individuals, AAO PWV indices demonstrated a strong relationship with each other ( R ≥ 0.86), but c-f PWV did not show high correlations with AAO PWV indices ( R ≤ 0.50). All AAO PWV indices increased with age ( P ≤ 0.05); however, c-f PWV did not increase from young to middle-aged ( P = 0.13) and middle-aged to old age groups ( P = 0.28). AAO PWV indices correlated well with C T ( R 2 ≥ 0.60), whereas c-f PWV did not ( R 2 = 0.23). Conclusion: The present study reveals that a complete understanding of large artery stiffness requires the direct assessment of proximal aortic stiffness rather than surrogate indices such as c-f PWV.