CIRCULATORY MECHANICS IN THE TOAD BUFO MARINUS I. STRUCTURE AND MECHANICAL DESIGN OF THE AORTA

This study describes several important mechanical design features of the aorta of a typical poikilothermic vertebrate. A strong functional similarity to the aorta of mammals is apparent, but some structural and mechanical differences are seen that reflect the lower pressure and simpler haemodynamics of the poikilothermic circulation. 1. The aorta is highly distensible, resilient and non-linearly elastic, giving it the requisite properties to act as an effective storage element in the arterial circulation. 2. An abrupt transition from high compliance (low elastic modulus) to relatively low compliance (high elastic modulus) takes place at pressures above the resting physiological range of 2-4 kPa. This behaviour reflects the composite nature of the artery wall in which rubbery elastin fibres and relatively rigid collagen fibres are the predominant elements. 3. The longitudinal tethering of the aorta when inflated is due primarily to anisotropy in elastic properties, rather than to links to the axial skeleton by branch vessels or connective tissue. 4. No significant changes in elastic properties or connective tissue content occur along the length of the toad arterial tree, in contrast to the situation in mammals