Longitudinal and Circumferential Strain of the Proximal Aorta

Abstract

BackgroundAccurate assessment of mechanical properties of the proximal aorta is a requisite first step for elucidating the pathophysiology of isolated systolic hypertension. During systole, substantial proximal aortic axial displacement produces longitudinal strain, which we hypothesize causes variable underestimation of ascending aortic circumferential strain compared to values in the longitudinally constrained descending aorta.Methods and ResultsTo assess effects of longitudinal strain, we performed magnetic resonance imaging in 375 participants (72 to 94 years old, 204 women) in the Age, Gene/Environment Susceptibility‐Reykjavik Study and measured aortic circumferential and longitudinal strain. Circumferential ascending aortic area strain uncorrected for longitudinal strain was comparable in women and men (mean [95% CI], 8.3 [7.8, 8.9] versus 7.9 [7.4, 8.5]%, respectively, P=0.3). However, longitudinal strain was greater in women (8.5±2.5 versus 7.0±2.5%, P<0.001), resulting in greater longitudinally corrected circumferential ascending aortic strain (14.4 [13.6, 15.2] versus 13.0 [12.4, 13.7]%, P=0.010). Observed circumferential descending aortic strain, which did not require correction (women: 14.0 [13.2, 14.8], men: 12.4 [11.6, 13.2]%, P=0.005), was larger than uncorrected (P<0.001), but comparable to longitudinally corrected (P=0.12) circumferential ascending aortic strain. Carotid‐femoral pulse wave velocity did not correlate with uncorrected ascending aortic strain (R=−0.04, P=0.5), but was inversely related to longitudinally corrected ascending and observed descending aortic strain (R=−0.15, P=0.004; R=−0.36, P<0.001, respectively). Longitudinal strain was also inversely related to carotid‐femoral pulse wave velocity and other risk factors for higher aortic stiffness including treated hypertension.ConclusionsLongitudinal strain creates substantial and variable errors in circumferential ascending aortic area strain measurements, particularly in women, and should be considered to avoid misclassification of ascending aortic stiffness.

Relations Between Aortic Stiffness and Left Ventricular Mechanical Function in the Community

“…Direct mechanical ventricular–vascular coupling provides an alternative explanation for the observed relation between aortic stiffness and LV systolic function. Systolic contraction shortens the LV long axis by pulling the aortic annulus and sinotubular junction of the aorta towards the LV apex, which moves minimally during systole 8, 9, 11. The combination of aortic annulus displacement along with minimal movement of the aortic arch implies that there is considerable longitudinal stretch of the ascending aorta during systole 10, 11, 41.…”

“…Systolic contraction shortens the LV long axis by pulling the aortic annulus and sinotubular junction of the aorta towards the LV apex, which moves minimally during systole 8, 9, 11. The combination of aortic annulus displacement along with minimal movement of the aortic arch implies that there is considerable longitudinal stretch of the ascending aorta during systole 10, 11, 41. Aortic stretch increases from the beginning until the end of systole and imposes a progressive systolic load on the heart 9, 12.…”

“…Longitudinal LV strain (also referred to as global longitudinal strain, GLS) appears to be a sensitive measure of impaired LV systolic function1, 2, 3 and has been shown in several studies to be better than ejection fraction at predicting cardiovascular disease events and death 4, 5, 6, 7. During systole, longitudinal shortening of the LV produces aortic displacement8, 9, 10 and stretches the ascending aorta 11. The force required to produce longitudinal strain of the aorta represents an often overlooked form of direct mechanical load on the LV that may have important implications for the relation between aortic stiffness and LV systolic function, particularly in the long axis 11, 12…”

“…During systole, longitudinal shortening of the LV produces aortic displacement8, 9, 10 and stretches the ascending aorta 11. The force required to produce longitudinal strain of the aorta represents an often overlooked form of direct mechanical load on the LV that may have important implications for the relation between aortic stiffness and LV systolic function, particularly in the long axis 11, 12…”

Cyclic Strain and Hypertension Increase Osteopontin Expression in the Aorta

“…The average circumferential cyclic strains that the cells of the aorta experiences ranges from 5 to 25% or more, depending on the physiologic state of the organism. 4,17,40 While the 10% strain used in the present study is within the range seen in vivo , because of the very artificial ex vivo conditions, one has to be cautious about quantitatively translating these findings to the in vivo setting. Instead, it is probably more appropriate to interpret the cell culture studies as proof of concept studies indicative of the fact that OPN expression is regulated by mechanical strain.…”