Design of the mammalian respiratory system. IX. Functional and structural limits for oxygen flow

This paper presents the synthesis and interpretation of a series of correlated studies of the mammalian respiratory system--measurements of maximal rate of O2 consumption, the lung's diffusing capacity, the mitochondrial volume, and the capillary number and length in skeletal muscle. It discusses the results with respect to the principle of symmorphosis, i.e. of morphogenesis adapted to functional needs. We find that the accumulated evidence supports this principle at all organizational levels considered, although the models used for structure-function correlation need further refinement.