[A mathematical model for the description of oxygen-diffusion in the intervillous space of the human placenta (author's transl)]

[Changes in the blood rheology and their influence on the oxygen diffusion in normal and pathological pregnancies (author's transl)]

Blood viscosity studies were carried out at regular intervals in 51 patients with normal pregnancy and in 27 patients with high risk pregnancy, i.e. with EPH-gestosis and placental insufficiency. During gestation the relative blood viscosity is significantly increased compared to 15 normal non-pregnant women. At a corrected hematocrit of 45% we found a direct correlation to plasma fibrinogen and to the blood sedimentation rate. Although the whole blood viscosity does not indicate any change in normal pregnant women, there is, however, a viscosity increase in the last trimester of high risk pregnancies. Additionally a mathematical model of the oxygen diffusion in the placental cotyledo demonstrates rapid decrease of the oxygen partial pressure in the maternal intervillous channel if the microcirculation of the "Placenton" is impaired.

A reflection on the oxygen diffusion of the terminal villus of the human placenta (author's transl)

By using a simple model, transformed to cartesian coordinates, we examined the behavior of the fetal and maternal oxygen partial pressure on the terminal villus of the human placenta during a constant arteriovenous oxygen difference. For this purpose we divided the flow length of the cotyledon in central and a peripheral part. We found that the oxygen exchange takes place at a lower utero-umbilical oxygen pressure gradient it the reduction of the maternal blood flow velocity amounts to 30% of the normal value and if the diffusion distance is doubled. However under these circumstances a sufficient the oxygen supply of the fetal organism. This is the case with the total flow length of a single cotyledon, but some of the terminal villi in the periphery of the cotyledon, could receive at the same time a diminished oxygen supply leading to degenerative cell changes. At a progression of these morphological changes or during labor the oxygen transport can get insufficient.