Axial nonuniformity of geometric and mechanical properties of mouse aorta is increased during postnatal growth

Abstract

The hemodynamic conditions of aorta are relatively uniform prenatally and become more heterogeneous postnatally. Our objective was to quantify the heterogeneity of geometry and mechanical properties during growth and development. To accomplish this objective, we obtained a systematic set of data on the geometry and mechanical properties along the length of mouse aorta during postnatal development. C57BL/6 mice of ages 1-33 days were studied. The ascending aorta was cannulated in situ and preconditioned with several cyclic changes in pressure. We investigated the axial variations of geometry (diameter and length) and mechanical properties (stress-stain relation, elastic modulus and compliance) of the mouse aorta from the aortic valve to the common iliac. Our results show that the arterial blood pressure of mice increased from approximately 30 to 80 mmHg during the first 2 wk of life. The stretch ratio, diameter, wall (intima-media) thickness, and total lumen volume of mouse aorta increased with age. The aorta was transformed from a cylindrical tube at birth to a tapered structure during growth. Furthermore, we found the mechanical properties were fairly uniform along the length of the aorta at birth and become more nonuniform with age. We conclude that the rapid change of blood pressure and blood flow after birth alter the geometric and mechanical properties differentially along the length of the aorta. Hence, the axial nonuniformity of the aorta increases as the organ becomes more specialized during growth and development.

Decreased aortic diameter and compliance precedes blood pressure increases in postnatal development of elastin-insufficient mice

“…The current study and an aging study in Eln ϩ/Ϫ mice (20) suggest that blood pressure begins increasing compared with WT in late postnatal development and continues to increase with aging. The measured blood pressures for WT mice in this study are consistent with previous data (12). Blood pressure is significantly increased in Eln ϩ/Ϫ mice at P14, which is later in development than significant reductions in the aortic pressurediameter and -compliance relationships at P7, supporting our hypothesis that changes in mechanical properties precede changes in blood pressure in these mice.…”

Biomechanics of the cardiovascular system: the aorta as an illustratory example

“…Huang et al (2006) showed a linear relationship in the outer (figure 14a) and inner diameter (data not shown) of the aorta with age. The growth rate of both the outer and the inner diameters of thoracic and abdominal aorta are different during the first two weeks of life (Huang et al 2006). 6.3.2.…”

“…The longitudinal retraction or pre-stretch is small in the young and increases with postnatal growth and development as the vessels are stretched by body growth (Dobrin et al 1975;Huang et al 2006). Zhang et al (2005) found that under the same physiological pressure, a more similar magnitude of circumferential and longitudinal stresses may be obtained by prestretching the vessel.…”

“…Aortic wall thickening was observed during development (Davis 1995;Olivetti et al 1980;Marchii & Becker 1997) and it was attributed to the medial tissue accumulation of elastin, collagen and smooth muscle cells. The wall thickness increases rapidly during the first two weeks of the mouse life (Huang et al 2006). Huang et al (2006) found that the growth of the wall thickness is not uniform along the aorta during development.…”

Towards the modelling of ageing and atherosclerosis effects in ApoE-/- mice aortic tissue

“…Several studies investigate the morphological, structural, and biochemical changes of the aorta as well as the relation between these changes and the mechanics of the aorta, see [9,16,20,32,33]. These studies confirm that the aorta increases its stenosis ratio, wall thickness, and mechanical stiffness during atherosclerosis.…”