Changes in the heart at birth
Circulation bypasses the lungs during gestation, but closure of shunt valves in the
heart re-routes blood to the lungs after birth.  Charles White (1773) pointed out that
this cannot be expected to happen instantaneously.  Circulation to the placenta
should be allowed to continue until the alveoli of the lungs have sufficient blood
supply to begin to receive oxygen in exchange for carbon dioxide.
    "Can it possibly be supposed that this
    important event, this great change which
    takes place in the lungs, the heart, and
    the liver, from the state of a foetus, kept
    alive by the umbilical cord, to that state
    when life cannot be carried on without
    respiration, whereby the lungs must be
    fully expanded with air, and the whole
    mass of blood instead of one fourth part
    be circulated through them, the ductus
    venosus, foramen ovale, ductus
    arteriosus, and the umbilical arteries and
    vein must all be closed, and the mode of
    circulation in the principal vessels entirely
    altered - Is it possible that this wonderful
    alteration in the human machine should be
    properly brought about in one instant of
    time, and at the will of a by-stander?"

White C (1773) A Treatise on the Management
of Pregnant and Lying-In Women. Canton, MA:
Science History Publications, 1987, p 45
Available from:
http://www.shpusa.com/bkindex.html
Charles White (1728-1813)
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