NEUTRAL AXIS LOCATION IN BENDING AND YOUNGS MODULUS OF DIFFERENT LAYERS OF ARTERIAL-WALL

With few exceptions, experimental results on the blood vessel elastici ty have been analyzed with the blood vessel wall treated as a homogene ous material, probably because the experiments have been limited to in flation and stretching. To advance the subject, we must evaluate the f orce-deformation relationship of different layers of the vessel. A key strategy to do this is to study nonaxisymmetric deformation of the ve ssel wall so that the different layers of the vessel may deform in dif ferent amounts at different places. One of the most effective nonaxisy mmetric deformations that can be imposed on the vessel wall is bending . The first important question to ask about bending is, Where is the n eutral axis? In this study, a method to determine the neutral axis is presented. We found that the neutral axis of the aorta of the pig lies in the medial layer about one-third of the wall thickness from the en dothelium. We measured the strain distribution in the vessel wall by o ptical methods. Using the load-deflection relationship, we evaluated t he Young's modulus of the intima-media layer and that of the adventiti a. They differ by an order of magnitude. Our results show that the You ng's modulus of the intima-media layer of the pig thoracic aorta is 43 .2 +/- 15.8 kPa, whereas the Young's modulus of the adventitial layer is 4.70 +/- 1.72 kPa, in a linear range of the stress-strain relations hip including the zero-stress state and the no-load state.