Absence of Po2 change in fetal brain despite Po2 increase in placenta in response to maternal oxygen challenge

Authors

  • I Huen,

    1. Centre for Imaging Sciences, University of Manchester, Manchester, UK
    2. The University of Manchester Biomedical Imaging Institute, University of Manchester, Manchester, UK
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  • DM Morris,

    1. Centre for Imaging Sciences, University of Manchester, Manchester, UK
    2. The University of Manchester Biomedical Imaging Institute, University of Manchester, Manchester, UK
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  • C Wright,

    1. Maternal and Fetal Health Research Centre, Institute of Human Development, University of Manchester, Manchester, UK
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  • CP Sibley,

    1. Maternal and Fetal Health Research Centre, Institute of Human Development, University of Manchester, Manchester, UK
    2. St Mary's Hospital, Central Manchester University Hospitals NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, UK
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  • JH Naish,

    1. Centre for Imaging Sciences, University of Manchester, Manchester, UK
    2. The University of Manchester Biomedical Imaging Institute, University of Manchester, Manchester, UK
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  • ED Johnstone

    Corresponding author
    1. Maternal and Fetal Health Research Centre, Institute of Human Development, University of Manchester, Manchester, UK
    2. St Mary's Hospital, Central Manchester University Hospitals NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, UK
    • Correspondence: ED Johnstone, Maternal and Fetal Health Research Centre, (Institute of Human Development), University of Manchester,

      St Mary's Hospital, Manchester M13 9WL, UK. Email edward.johnstone@manchester.ac.uk

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Abstract

Objective

Magnetic resonance imaging allows the noninvasive observation of Po2 changes between air breathing and oxygen breathing through quantification of the magnetic longitudinal relaxation time T1. Changes in Po2 are proportional to changes in the longitudinal relaxation rate ΔR1 (where ΔR1 = 1/T1oxygen − 1/T1air). Knowledge of this response could inform clinical interventions using maternal oxygen administration antenatally to treat fetal growth restriction. We present in vivo measurements of the response of the fetal–placental unit to maternal hyperoxia.

Design

Prospective cohort.

Setting

Large tertiary maternity hospital.

Sample

Nine women undergoing low-risk pregnancy (21–33 weeks of gestation) and five nonpregnant adults.

Methods

During imaging the air supply to mothers was changed from medical air (21% oxygen) to medical oxygen (100% oxygen) and T1 was monitored over time in both the placenta and fetal brain using a periodically repeated magnetic resonance imaging sequence. To demonstrate that the method could detect a brain response, brain responses from five normal adult volunteers were measured using a similar imaging protocol.

Main outcome measure

Changes in T1 following oxygen challenge.

Results

No significant ΔR1 (= 0.42, paired t-test) was observed in fetal brains. A significant placental ΔR1 (= 0.0002, paired t-test) of 0.02 ± 0.01/s (mean ± SD) was simultaneously observed in the same participants. In the brains of the nonpregnant adults, a significant ΔR1 (= 0.01, paired t-test) of 0.005 ± 0.002/s was observed.

Conclusion

Short-term maternal oxygen administration does not improve fetal brain oxygenation, in contrast to the response observed in the adult brain.

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