Comparative Study of Human and Murine Aortic Biomechanics and Hemodynamics in Vascular Aging

FIGURE 1. Pressure-diameter curves for the ascending thoracic aorta (ATA) of young (dashed line) and old (solid lines) adult subjects with corresponding values of in vivo axial stretch (λz, from literature data) and circumferential stretch (λθ, iteratively calibrated). Linearized stiffness (red lines) were used in our FSI simulations. For the humans (top), curves are recreated from best-fit values of the 8 material properties from Roccabianca et al. (2014) with in vivo circumferential stretches adjusted until in vivo mean pressures corresponded with in vivo mean diameters. For the mice (bottom), the pressure-diameter curves were measured directly in vitro, with best-fit values of the material parameters determined via non-linear regression of the biaxial data.

FIGURE 2. ATA inflow waveforms (mL/s) and associated values of CO (L/min).

FIGURE 3. (A) 3D models of the aorta and main branches for each subject along with body mass, height (for humans), and aortic length. Percent differences between young and old adults for each species is shown for mass and aortic length. Anatomical models are shown in the same scale between age groups, but not between species. (B) Percent changes in inner diameter by region (pDTA, proximal descending thoracic aorta; dDTA, distal descending thoracic aorta; SAA, suprarenal abdominal aorta; and IAA, infrarenal abdominal aorta) of the aorta in comparison to the young ascending thoracic aorta (ATA_ diameter) for both species.

FIGURE 4. Regional circumferential (Cθθθθ) and axial (Czzzz) material stiffness and wall thickness h for young adult and old adult humans (top) and mice (bottom) for five locations along the aorta (ATA, ascending thoracic aorta; pDTA, proximal descending thoracic aorta; dDTA, distal descending thoracic aorta; SAA, suprarenal abdominal aorta; and IAA, infrarenal abdominal aorta). The percentages indicate changes with aging relative to the young value. Note that the ATA stiffened the most with aging in humans (cf. Redheuil et al., 2010) whereas the DTA stiffened the most with aging in mice.

FIGURE 5. Total resistance RTOT and compliance CTOT broken into components of the central (3D) and peripheral vasculature.

FIGURE 6. Volume rendering of blood velocity at peak systole for the humans (left) and mice (right), with pressure and flow waveforms at three sites along the aorta (ATA, ascending thoracic aorta; DTA, descending thoracic aorta; and IAA, infrarenal abdominal aorta) (center).

FIGURE 7. Validation of hemodynamic results using pressure data. For humans, the simulated left subclavian artery pressure (solid red line) compared well with systolic and diastolic pressure cuff values (dashed black lines). For the mice, simulated ascending thoracic aortic (ATA) flow waveforms (solid red lines) compared well with experimental data from multiple subjects (dashed lines).

FIGURE 8. Computed values of mean arterial pressure (MAP) for five aortic locations (ATA, ascending thoracic aorta; pDTA, proximal descending thoracic aorta; dDTA, distal descending thoracic aorta; SAA, suprarenal abdominal aorta; and IAA, infrarenal abdominal aorta) and an iliac artery for all four primary study groups, all showing modest changes proximal to distal.

FIGURE 9. Pulse pressure amplification manifests in the human aorta, but not the mouse.

FIGURE 10. Aorto-iliac PWV (left) and spatially weighted averages of structural aortic stiffness (right) for the humans and mice. Percent difference from young to old are indicated for both species. Baseline values for the young subjects were 6.9 m/s for human and 3.2 m/s for mouse PWV and 1195.7 and 15.3 for human and mouse structural stiffness.