Aortic elastic properties with transesophageal echocardiography with automated border detection: validation according to regional differences between proximal and distal descending thoracic aorta.

We have previously described the use of transesophageal echocardiography with automated border detection to quantify regional aortic elastic properties. The purpose of this study was to validate this technique further by measuring regional variations of aortic elastic properties and comparing them with previously published data acquired by invasive methods. In nine anesthetized, closed-chest dogs, aortic pressure and lumenal area (transesophageal echocardiography with automated border detection) signals were recorded simultaneously at two aortic sites: just distal to the branching site of the left subclavian artery (proximal) and at the level of the diaphragm (distal). Instantaneous wall thickness was estimated by combining M-mode measurement of aortic end-diastolic thickness with instantaneous lumenal area. Data were acquired over a wide range of loading conditions, generated by inferior vena caval balloon occlusion. Aortic compliance per unit length, midwall radius, midwall stress, and incremental elastic modulus were computed. Aortic midwall radius and incremental elastic modulus values for proximal and distal aortic sites were compared at a common level of midwall stress. Compliance per unit length was higher in the proximal compared with the distal descending thoracic aorta (0.013 +/- 0.003 versus 0.008 +/- 0.003 cm2/mm Hg; mean +/- SD; p = 0.0011). Midwall radius was larger at the proximal location (0.76 +/- 0.07 cm versus 0.64 +/- 0.07 cm; p = 0.0001), whereas incremental elastic modulus was greater distally (0.799 +/- 0.052 dynes x 10(6)/cm2 versus 0.912 +/- 0.130 dynes x 10(6)/cm2; p = 0.02). Lower compliance values at the distal site of the descending thoracic aorta resulted from greater wall stiffness and a smaller radius. Transesophageal echocardiography with automated border detection provides reliable measurements of instantaneous aortic areas necessary for quantifying regional elastic properties.