Reduced ascending aortic strain and distensibility: earliest manifestations of vascular aging in humans

Abstract

Arterial stiffness predicts cardiovascular events beyond traditional risk factors. However, the relationship with aging of novel noninvasive measures of aortic function by MRI and their interrelationship with established markers of vascular stiffness remain unclear and currently limit their potential impact. Our aim was to compare age-related changes of central measures of aortic function with carotid distensibility, global carotid-femoral pulse wave velocity, and wave reflections. We determined aortic strain, distensibility, and aortic arch pulse wave velocity by MRI, carotid distensibility by ultrasound, and carotid-femoral pulse wave velocity by tonometry in 111 asymptomatic subjects (54 men, age range: 20 to 84 years). Central pressures were used to calculate aortic distensibility. Peripheral and central pulse pressure, augmentation index, and carotid-femoral pulse wave velocity increased with age, but aortic strain and aortic arch PWV were most closely and specifically related to aging. Ascending aortic (AA) strain and distensibility decreased, respectively, by 5.3+/-0.5% (R(2)=0.54, P<0.0001) and 13.6+/-1 kPa(-1)x10(-3) (R(2)=0.62, P<0.0001), and aortic arch pulse wave velocity increased by 1.6+/-0.13 m/sec (R(2)=0.60, P<0.0001) for each decade of age after adjustment for gender, body size, and heart rate. We demonstrate in this study a dramatic decrease in AA distensibility before the fifth decade of life in individuals with diverse prevalence of risk factors free of overt cardiovascular disease. In particular, compared with other measures of aortic function, the best markers of subclinical large artery stiffening, were AA distensibility in younger and aortic arch pulse wave velocity in older individuals.

Figure 1

Aortic arch PWV assessment with MRI and cfPWV measured by tonometry. cfPWV assessed with carotid–femoral tonometry in a young (A) and older participant (B). Corresponding measurements of aortic arch PWV (C and D) showing simultaneously acquired normalized flow curves by phase-contrast MRI in the ascending and descending aorta. The younger participant shows preserved aortic elasticity (normal pulse wave velocities), whereas the older participant presents increased pulse wave velocities in relation with a stiffer aorta. Δt indicates transit time; D, transit distance; x axis, time in milliseconds; y axis in arbitrary units.

Figure 2

Effect of age on measures of proximal aortic function. A, AA strain (dot) and distensibility (squares) by decades of age. B, AA distensibility (age <50=red dots and ≥50 years=blue dots). C, Aortic arch PWV (dark squares) and cfPWV (open squares) by decades of age. D, Aortic arch PWV (red dots, <50 years of age; blue dots, ≥50 years of age).