A useful line of analysis is to consider the effect of scale changes for creatures which are similar in shape and only differ in scale. As the scale of an animal increases the body weight and volume increase with the cube of scale. The volume of blood flow required to feed that bulk also increases with the cube of scale. The cross sectional area of the arteries and the veins required to carry that blood flow only increases with the square of scale. There are other area-volume relationships which impose limitations on creatures. Some of those area-volume constraints, including the cross sectional area of the arteries, play an important role in determining the longevity. Thus to compensate for the body needs which increase with the cube of scale but the areas increase with only the square of scale the average blood flow velocity must increase linearly with scale. Blood flow velocity is driven by pressure differences.
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