Journal of Applied Physiology, Vol 42, Issue 2 179-190, Copyright © 1977 by American Physiological Society
Fetal O2 changes in response to hypoxic stress: a mathematical model
W. W. Allen, G. G. Power and L. D. Longo
We developed a mathematical model to compute the time course of PO2 changes
in fetal blood vessels during hypoxia. The model represents the circulation
and major organs as a system of paths and nodes. We calculated outflow O2
for a path from its inflow O2 content and its distribution of transit
times. The O2 content at a given node equals the flow-weighted sum of O2
delivered by different paths. Placental O2 transfer and organ O2
consumption are related to their arterial PO2 levels. We simulated the
effects of uterine contractions with Gaussian-shaped decreases in placental
O2 transfer. Increasing the intensity and increasing the duration of
hypoxic episodes have comparable effects. Liver O2 consumption decreases
more than that of other organs during hypoxic episodes. At the peak of a
contraction, fetal systemic PO2 values decrease only about one-fourth as
much as those in end-capillary placental blood. This indicates that despite
rapid circulation times, fetal O2 reserves protect it against severe, short
term hypoxia.
