In VivoAssessment of Luminal Cross-Sectional Areas and Circumferential Tension-Strain Relations of the Porcine Aorta

Abstract

The objectives were to measure the pressure--cross-sectional area relations and intrinsic stiffness of the porcine aorta in vivo. Measurements were made in 12 pigs, weight 30, 50 or 75 kg, proximal and distal to the bifurcation of the renal arteries, using an electrical impedance system which was located inside a balloon mounted on a catheter. Vessel cross-sectional area (CSA) was assessed by measuring impedance of the fluid inside the balloon during distension. In vitro testing demonstrated the accuracy and reproducibility of impedance planimetry. In vivo steady-state CSA values showed non-linear relationship with rising distension pressures. Mean CSA values rose with increasing weight of the pigs. the suprarenal aorta was larger than the infrarenal only in 75 kg pigs (p < 0.05). At three measurements the within-subject variation was 0.89% and the between-subject variation 99.11%. Nitroglycerine infusion produced only minor, insignificant CSA increase, indicating negligible tone in the abdominal aorta. All segments showed circumferential wall strain-tension relations with exponential behaviour uninfluenced by weight class or site in the aorta. Information of vascular mechanics in vivo is obtainable by catheterization of the abdominal aorta.