The static elastic properties of 45 human thoracic and 20 abdominal aortas in vitro and the parameters of a new model

Segments of 45 human thoracic and 20 abdominal aortas, including 13 pairs, aged 30-88 yr at autopsy, were perfused with 37 degrees C Tyrode's solution at in-situ length. Diameter changes due to 20 mmHg pressure steps, between 20 and 180 mmHg, were measured to 1 micron accuracy with balanced transducers. Absolute diameter at 100 mmHg was measured to 50 micron accuracy. At 100 mmHg, cross-sectional area ranged from 2.6 to 7.6 for thoracic and from 1.0 to 3.2 cm2 for abdominal segments. Compliances ranged from 1.9 to 17 for thoracic and from 0.6 to 4.4 mm3/mmHg.cm for abdominal segments. An arctangent model with three free parameters A(p) = Am(1/2 + tan-1 [p-p0)/p1)/pi) explained over 99% of the variance in area with pressure for each aorta. Changes in compliance, characteristic impedance and propagation velocity are equally well described. Abdominal fits on the average appeared down scaled by a factor of 2 and shifted 20 mmHg towards lower pressures from paired thoracic (significant at p = 0.001).