P46 Elongation of the Proximal Aorta During the Cardiac Cycle Plays an Important Role in the Estimation of Aortic Compliance

Abstract

Background and Aims

Arterial volume compliance is a major determinant of cardiac afterload. More than 50% of the arterial volume compliance resides in the proximal aorta. Researchers often use area compliance for the estimation of volume compliance, assuming an invariant vessel length over pressure changes. Recent studies have provided evidence to question this simplification, showing that the extension of the proximal aorta along its long axis during systole produces significant longitudinal strain, which could lead to erroneous estimation of arterial stiffness. The aim of the present study was to test this hypothesis in a computational environment.

Methods

The 3-D proximal aortic geometry of a healthy young male was reconstructed and meshed and the original zero-pressure geometry was restored. Material behavior was approximated based on the model of (1). Viscoelastic support conditions were introduced along the aortic wall and aortic root motion, estimated from the cardiac-gated CT data of a healthy subject, was enforced at the proximal boundary. The simulation was run for an input pressure ranging from 80-110mmHg. Volume compliance of the vessel as obtained by integrating the area compliance over the centerline length (both variable and invariable) was subsequently compared to the ground truth (which was imposed by the material stiffness).

Results

Integration of the area compliance over an invariable centerline length led to an underestimated average distensibility by −68%. After taking into account the elongation, the error was improved to -25% (Figure 1).

Conclusion

The elongation of the aorta during cardiac cycle was found to affect significantly the estimation of arterial compliance.