Constructal Theory and Flow Architectures in Living Systems

We ap ply Constructal the ory to the study of the flow struc ture of the hu man re spi ra tory tree. We show that the flow ar chi tec ture that would per form ox y gen a tion of the blood and re moval of car bon di ox ide best, i. e. with low est re sis tance, would be com posed of a chan nel sys tem with 23 bi fur ca tion with a dif fu sive zone (alveolus) at the end. As this tree matches the hu man re spi ra tory tree we con clude that na ture has op ti mized it in time. Two constructal re la tion ships also emerge: (1) the length l, de fined by the ra tio of the square of the air way di am e ter to its length, is con stant for all in di vid u als of the same spe cies, and (2) the length l is re lated to the vol ume of the space al lo cated to the re spi ra tory pro cess, to the length of the re spi ra tory tree and to the area of the al ve oli, and de ter mines univocally the branch ing level of the re spi ra tory tree.