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Key Words
Thoracic aorta * Moens-Korteweg equation * Histomorphometry * Distensibility coefficient * Medial thickness
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 (EMK) 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 (Einc) 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^sub inc^ 8.9 +/- 0.5 and 5.7 +/- 0.4 * 10^sup 6^ dyne/cm^sup 2^, p < 0.05; E^sub MK^ 7.6 +/- 0.5 and 4.1 +/- 0.5 * 10^sup 6^ dyne/cm^sup 2^, p < 0.05. E^sub inc^ was greater than E^sub 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.
Introduction The wall of the large-diameter elastic arteries (aorta and carotid arteries) becomes progressively stiffer with age, hypertension and other vascular diseases; this leads to a decrease in arterial compliance and an increase in the pulsatile element of pressure [1]. The latter is a strong indicator of cardiovascular risk [2, 3]. The age-related decline in wall distensibility increases aortic input impedance and this adversely affects cardiac function and structure [4].
Direct measurement of the elastic behavior of the aortic wall in vivo is based mainly on two approaches. Measurement of pressure pulse wave velocity (PWV) provides values for elastic modulus via the Moens-Korteweg equation. This was first developed to measure aortic elasticity in large mammal species (humans [5]...