Can Rupture Pressure of Thoracic Aortic Aneurysms Be Estimated from Their Pulsatile Deformation?

Abstract

To predict the rupture of thoracic aortic aneurysms (TAAs), the relationship between stiffness and rupture pressure was investigated in a pressure-imposed test. Each quadrilateral (ca. 20×20 mm²) specimen of human TAAs or porcine thoracic aortas (PTAs) was pressurized until rupture or up to 4500 mmHg. Tension per unit length (T) and strain (ε) of the specimen were calculated from loaded pressure (P) and deformations of the specimen. Stiffness (S) was determined as the slope of the T-ε curve. Blood pressure in vivo (P_vivo) was estimated from P, T, and diameter of the specimen. Stiffness of PTA specimens increased with an increase in P_vivo, while that of TAA specimens reached a plateau in a low-P_vivo region. To evaluate this phenomenon quantitatively, a yielding parameter (τ_P), i.e., P_vivo at which the stiffness S reached a plateau level, was determined by fitting an equation S=C_P{1–exp(–P_vivo/τ_P)} to the S-P_vivo curve. The parameter τ_P correlated significantly with the rupture pressure in vivo. This parameter also correlated significantly with the area fraction of collagen, indicating that collagen composition caused changes in the τ_P in TAA. Since the yielding parameter can be obtained from clinical data, τ_P can be used for rupture risk estimation.