Avni R1, Garbow JR2, Neeman M1
1Department of Biological Regulation, Weizmann Institute of Science, Rehovot, Israel, 2Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri, USA
Oxygen transport, one of several key functions performed by the placenta, depends primarily on placental oxygen pressure gradient and the oxygen affinity of fetal and maternal blood. To compensate for its low oxygen tension environment, fetal hemoglobin has a greater oxygen affinity than adult hemoglobin. Obtaining oxygen-hemoglobin dissociation curves and extracting P50 values, characteristic of oxygen affinity, may provide useful information, both in animal models and in clinical settings. We describe a novel, non-invasive MRI method for deriving MRI-based oxygen-hemoglobin dissociation curves.
Pregnant ICR mice were analyzed using a gradual respiration challenge from hyperoxia to hypoxia on E14.5 (n=8 mice; 58 fetuses), and E17.5 (n=10 mice; 89 fetuses). R1 and [1-∆R2*/R2*] values derived in the placenta, fetal liver and maternal liver at each oxygen phase demonstrated the expected sigmoid-shaped curve, with a clear difference between adult and fetal tissues, manifested by a shift to the left in the curves (Figure A). Apparent P50 (AP50) values, derived from the curves, demonstrate significantly lower AP50 values in fetal liver than in maternal liver (Figure B). AP50 maps inside the placenta and fetal liver show heterogeneity within these tissues (Figure C).
In conclusion, we present here a non-invasive approach to probe and quantify oxygen transfer across the placenta. This method may be useful for evaluation of fetal health.
Figure (A) Representative examples of MRI-based oxygen hemoglobin dissociation curves in placenta, fetal liver and maternal liver; (B) Mean apparent P50 values on E14.5; (C) Representative AP50 maps inside the placenta and fetal liver on E14.5.