Measurements of Young's modulus of elasticity of the canine aorta with ultrasound.

We have developed an ultrasonic technique for determining the dynamic Young's modulus of elasticity (E) of the canine aorta in vivo. Young's modulus was measured in the descending thoracic aorta (DTA) and the abdominal aorta (AA) of 12 dogs over a range of mean blood pressures from 40-200 mmHg. The vessels were excised and dynamic moduli were determined in vitro postmortem from pressure-volume curves. The data so obtained were compared to the in vivo values. In vivo and in vitro moduli increased exponentially with mean distending pressure (P). The equation of best fit for these data was of the form E= E0 exp(aP). Constants E0 and a depended on the site of measurement (AA or DTA) and upon the particular animal. In vivo and in vitro moduli were not significantly different in the AA (AA: in vivo E0 = 667 ± 382 mmHg, a = 0.017 ± 0.004 mmHg; in vitro E0 = 888 ± 367, a= 0.016 ± 0.002). However, in vivo moduli exceeded in vitro moduli in the DTA. (DTA: in vivo E0 = 687 ± 241, a = 0.016 ± 0.004; in vitro E0 = 349 ± 64, a= 0.018 ± 0.003). The increased stiffness of the DTA compared to the AA in vivo may be due to the in situ tethering of the aorta to the spine by the parietal pleura.