Volumetric Ultrasound Analysis of the Abdominal Aorta Enhances Strain Assessment in Hypertensive Mice

Abstract

Aortic stiffness (AS) is a well-described and underutilized predictor of cardiovascular morbidity and mortality, particularly in hypertension (HTN). Employing noninvasive ultrasound technology to quantify AS metrics could have therapeutic application, but regional variation has compromised integration. We hypothesize that integrating 4-dimensional (4D) ultrasound with volumetric analysis will enhance the AS analysis in hypertensive mice as a foundation for clinical translation. Systolic blood pressure (SBP) was captured by Coda tail-cuff in normotensive C57Bl/6 mice (n = 3) on day 0. Under inhaled anesthetic, the Vevo3100 high-resolution micro-ultrasound was utilized to capture images of the infrarenal aorta which included (1) axial plane at three segments (proximal, middle, and distal); (2) longitudinal plane; and (3) 4D images of volumetric changes across the cardiac cycle. VevoVasc software enabled quantification of distensibility, pulse propagation velocity, global radial strain, and volumetric strain (VS). HTN was then induced by osmotic pump angiotensin-II infusion (1.46 mg/kg/day). SBP and ultrasound measurements were reassessed at 21 days. The t test was utilized to compare strain metrics at day 0 vs 21 with significance at P < .05. With AngII infusion, SBP increased 32 ± 2% (P < .05). Values for distensibility significantly decreased from proximal to distal aortic regions at day 0, and demonstrated a 50 ± 5% reduction with HTN at day 21 (P < .05). As another indicator of aortic stiffness in HTN, pulse propagation velocity increased >2.8-fold. Global radial strain, on the other hand, provided discordant results along the axial aortic regions at day 0 as well as day 21, and no change could be detected in the longitudinal plane. With 4D ultrasound to capture volume and normalize by pulse pressure to create the VS analysis, however, we detected a significant reduction in VS (0.74 ± 0.3 μL/mm Hg to 0.36 ± 0.1 μL/mm Hg; P < .05) to effectively quantify infrarenal aortic strain as an indicator of increased AS. Methodology to ensure sensitive, specific, and reproducible quantification of AS is vital to establishing clinical utilization. Ultrasound-derived VS analysis decreased regional variability and further investigation is warranted to define this technique in the medical management of HTN and other regional aortic pathology.