Variability and reproducibility of carotid structural and functional parameters assessed with transcutaneous ultrasound - results from the SAPALDIA Cohort Study.

OBJECTIVE: Carotid intima media thickness (CIMT) and local stiffness are vascular biomarkers of atherosclerotic burden. We investigated the variability and reproducibility of clinically relevant structural (CIMT, lumen diameter) and functional parameters (strain, distensibility, compliance, β-stiffness index, Peterson's elastic modulus and Young's elastic modulus) measured in B-mode ultrasound sequences of the common carotid artery in the second follow up of the Swiss Cohort Study on Air Pollution and Lung and Heart Diseases In Adults (SAPALDIA3).
METHODS: Ultrasound sequential images were examined twice over a 1 cm segment across at least one heart cycle in 165 SAPALDIA3 participants. To assess variability and reproducibility of structural and functional parameters, individual coefficients of variation (CV), intraclass correlation (ICC), Bland-Altman plots and mixed effect regressions were used.
RESULTS: ICCs of repeated examinations ranged between 0.67 and 0.77 for blood pressure indices, between 0.87 and 0.97 for structural properties and between 0.75 and 0.79 for functional parameters. CV was lowest in structural parameters (1.6-4.6%), followed by blood pressure (5.1-7.9%) and functional indices (11.0-13.1%). Variations in all parameters were predominantly explained by subjects (>74% in functional, >82% in structural properties). Bland-Altman plots for functional indices showed mean and standard deviation of the respective mean value of 4.2(19.6)% for strain, 1.9(24.4)% for distensibility, 2.4(22.2)% for compliance, 3.0(24.4)% for β-stiffness index, 0.9(25.7)% for Peterson's elastic modulus and 1.2(27.9)% for Young's elastic modulus.
CONCLUSION: The results show that SAPALDIA3 measurements of transcutaneous ultrasound examinations have an excellent reproducibility of structural parameters and a good reproducibility of functional indices.