The passive mechanical properties of the dorsal aorta and the vena cava of Octopus vulgaris were investigated in vitro. Both vessels are highly distensible structures that exhibit non-linear elasticity, but have substantially different material properties. The volume compliance of each vessel is maximal within the resting physiological pressure range (2–3 kPa in the aorta and 0–0.5 kPa in the vena cava) but is five times greater in the vena cava than in the aorta. The aorta is mechanically suited to function as an elastic storage reservoir in the arterial circulation, while the vena cava is appropriately designed to be a low-pressure capacitance element.

Pressure wave velocity in the aorta was calculated from the elastic modulus to be 1.8 ms−1 under resting conditions. Therefore, pressure changes will occur almost simultaneously throughout the arterial tree and pressure wave transmission properties can be described by a two-element Windkessel model. Predictions of vascular impedance amplitude made from this model are presented.

The effectiveness of the aorta as an elastic reservoir appears to be severely reduced during exercise in Octopus. Because blood pressure increases while heart rate does not, the efficiency of the Windkessel will be diminished as the time constant of the system decreases and the pulsatile work of the heart subsequently increases.

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