Determination of Aortic Elastic Modulus by Pulse Wave Velocity and Wall Tracking in a Rat Model of Aortic Stiffness

Abstract

Several methods have been used to evaluate the elastic modulus of the aortic wall in the rat, but these have never been compared when used simultaneously. We measured thoracoabdominal pulse wave velocity (PWV) and changes in thoracic aorta diameter during the cardiac cycle (with wall echo-tracking) in pentobarbital-anesthetized adult male Wistar rats; half of the group had previously received vitamin D₃ plus nicotine (VDN) in order to increase the stiffness of the aortic wall. The Moens-Korteweg elastic modulus (E_MK) was calculated from PWV and the ratio of the internal diameter to the medial thickness determined by histomorphometry following in situ pressurized fixation. The incremental elastic modulus (E_inc) was calculated from the distensibility coefficient and end-diastolic diameter measured by wall echo-tracking and the medial thickness determined by histomorphometry. Both values were higher in VDN rats than in controls: E_inc 8.9 ± 0.5 and 5.7 ± 0.4·10⁶ dyne/cm², p < 0.05; E_MK 7.6 ± 0.5 and 4.1 ± 0.5·10⁶ dyne/cm², p < 0.05. E_inc was greater than E_MK and this was partially due to the fact that the in vivo end-diastolic diameter measured by ultrasound was greater than the mean aortic diameter measured ex vivo by histomorphometry. In conclusion, different methods for the measurement of the elastic properties of the aortic wall gave similar results in controls and in a rat model of aortic stiffness.