Measurement of regional elastic properties of the human aorta: A new application of transesophageal echocardiography with automated border detection and calibrated subclavian pulse tracings

Abstract

Background: Evaluation of regional aortic elastic properties in humans has been hampered by the need for invasive techniques to access instantaneous aortic pressure, wall thickness, and cross-sectional area or diameter. In this study, a new noninvasive method is presented for quantification of regional aortic elastic properties. Methods and Results: Twenty-five patients were studied during transesophageal echocardiographic procedures. Measurements of instantaneous aortic cross-sectional area were obtained with an automated border detection algorithm applied to short-axis transesophageal two-dimensional echocardiographic images of the proximal descending thoracic aorta. Instantaneous aortic wall thickness was derived from combined two dimensional targeted M-mode end-diastolic wall thickness and instantaneous aortic measurements. Instantaneous aortic pressures were estimated from calibrated subclavian pulse tracings recorded simultaneously. Data were digitized to generate aortic area-pressure loops. Regional aortic mechanical properties were quantified in terms of compliance per unit length (C is the slope of the area-pressure regression), aortic midwall radius (R(m)), and incremental elastic modulus of the aortic wall (E(inc)). To assess the independent effect of age, R(m) and E(inc) values were compared at a common level of aortic midwall stress (0.666 x 106 dynes/cm2). Mean values (±SD) for C, R(m), and E(inc) were 0.01±0.004 cm2/mm Hg, 1.14±0.17 cm, and 7.059±4.091 x 106 dynes/cm2, respectively. An inverse linear correlation was found between aortic compliance per unit length and age (r=-.68, P