Morphometric estimation of pulmonary diffusion capacity. VII. The normal Guinea pig lung

A study of 15 normal adult guinea pig lungs fixed by instillation of fixatives via the airways is described. The morphological appearance of the guinea pig lung is similar to that of other mammals apart from quantitative differences in the mass of connective tissue in the alveolar-capillary barrier whose mean thickness was estimated at 1.59 mum. Lung volume, alveolar volume, capillary volume and the surface areas of alveoli and capillaries are shown to be linearly related to body weight. Analysis of the morphometric diffusion capacities of the alveolar-capillary membrane and of the lung shows that these are also linearly related to body weight. For a mean body weight of 429 g the lung volume was 13 ml, the alveolar surface 0.91 m2, the capillary volume 1.5 ml, the harmonic mean barrier thickness 0.42 mum, and DL 2.13 ml/min.mm Hg. These parameters are compared with those of other mammalian species and discussed in the context of normal activity levels as a probable important adaptive factor determining the size of the gas exchange apparatus.