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.

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Evaluation was made of the circadian rhythm of blood pressure (BP) by using ABPM in patients with CKD. There was a substantial difference in the relationship between heart rate (HR) and BP in 3 CKD modalities (ND (non-dialysis), HD (hemodialysis), and PD (peritoneal dialysis). Such differences were characterized by a greater BP level in HD, and the predominance of non-dipper pattern in PD. Despite the assessment by cardio-ankle vascular index (CAVI), coefficient of variation of R-R intervals (CVRR) and ultrasonic echocardiography (UCG), reasons to explain the difference in the HR-BP relationship were unknown. Future studies will be needed to further investigate the usefulness of ABPM in CKD.

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