The Transport of Oxygen in the Sheep's Placenta: The Diffusion Constant of the Placenta *

The problem of how oxygen is transferred from lung alveoli to blood was considered in 1909 by Christian Bohr,' who used the calculus to develop the appropriate equation for the diffusion of oxygen from alveoli into blood and presented a graphical solution. In this way, the integrated mean oxygen pressure gradient causing oxygen transfer across the alveolar membranet was obtainable and, in addition, the diffusion constant of the lungs. While the theoretical basis was then at hand, refinements in experimental techniques were needed to yield further knowledge of the transfer of oxygen in the lungs. Lilienthal, Riley, et al.' have contributed substantially to the understanding of this process and their paper refers to other notable contributions since Bohr's. The pulmonary methods of Bohr do not seem to have been applied to the more complex transport of oxygen from maternal to fetal blood, although the data for such an application, in the case of the sheep, are now at hand.1'' We shall develop the theory of diffusion across the placental membrane separating maternal and fetal blood in the sheep and then apply it to a sample set of the data available.