Figure 7.
(a) Diameter as a function of order number for trees with 1000 vessels. Decreasing mb, which describes the relative energy cost of an amount of blood and the power required to pump it, has little effect on the agreement of the diameters with morphological data. (b) For lengths however there is an obvious effect in the larger arteries, with regimes of high pumping cost being more accurate. The primary optimization for high pumping cost then is to increase the length of the largest arteries. (c,d) The main effect is a change in the asymmetry of the branching of the largest arteries—for large mb, the branches are more symmetric than for small mb. As mb becomes very small, the limiting behaviour is broad trunks that wind around all the tissue, with a large number of very small offshoots that supply blood in the direct vicinity of the large vessel.