2 – Prolonged partial asphyxia
In Myers' (1972) experiments, prolonged partial
asphyxia was produced before birth, in most cases by
mechanical constriction of the materal abdominal
aorta (distal to the renal arteries).  Other
manipulations included: (a) partial placental ablation,
(b) catecholamine infusions into the maternal
circulation to produce maternal visceral
vasoconstriction, (c) use of fluorothane to produce
maternal hypotension, and near-term (d) infusion of
excessive oxytocin into the maternal bloodstream,
which stimulated frequent strong uterine contraction.  
All of these methods reduced maternal blood flow
and perfusion of the placenta [1].

Fetal heart-rate, blood pressure, blood oxygen, and
degree of acidosis were monitored and correlated
with three identifiable postnatal outcomes:

  1. Mild asphyxia with pH levels maintained above
    7.10 and fetal blood oxygen above 1.5 to 2.0
    volumes percent resulted in no evidence for
    brain injury on either clinical or pathological
    examination.
  2. Severe asphyxia with pH below 7.00 and fetal
    blood oxygen below 0.4 to 0.8 percent
    enduring for several hours leads to fetal death
    from heart failure.  Even if resuscitated and
    maintained in intensive care for many hours,
    the newborn monkeys were unable to maintain
    normal blood pressure and died due to
    progression of hypotension.  Brain pathology
    was difficult to evaluate because of their short
    survival, but brain swelling and necrosis in the
    cerebral hemispheres was noted.
  3. Intermediate degrees of asphyxia permitted
    survival but with evidence of permanent injury
    of the brain and heart.  "Asphyxial myocardial
    decompensation" was identified as a factor in
    impaired postnatal circulation and consequent
    diminished perfusion of the brain.  Swelling of
    the brain was discussed as a further
    compounding factor, "Severe brain swelling
    expressed the blood from the cerebral
    vasculature, leaving the entire brain pale and
    bloodless" [1, p265].
  1. Myers RE (1972) Two
    patterns of perinatal brain
    damage and their
    conditions of occurrence.  
Reference