4 – Sudden total asphyxia revisited
Myers devoted the beginning of his 1972 paper to a
careful review of physiological findings from
experiments on "acute total asphyxia" at birth in which,
"Term fetal monkeys are exposed to rigorously timed
episodes of total asphyxia by slipping a thin, saline-
filled rubber sac over the fetal head at surgical
delivery and clamping the umbilical cord. The
envelopment of the fetal head prevents onset of air
breathing while the clamping of the umbilical cord
abruptly halts fetal placental circulation." [1, p247].
This graphic description should be appreciable by just
about everyone.
Events that take place during abrupt catastrophic
asphyxia were described by Myers in great detail.
Heart rate drops within 20 to 30 seconds after oxygen
in the blood is exhausted to a rate of 60 excitations
per minute, representing the heart's basal rate in the
absence of oxygen. Slowing of heart rate during
asphyxia therefore represents a mechanism for
preservation of this organ.
Normal pH was reported as 7.28 to 7.34 but fell
steadily to 6.7 as carbon dioxide was converted to
bicarbonate. Blood oxygen was depleted within the
first minute and a half; and, "By the end of another
minute, all energy transformations carried out in the
fetal organs and tissues take place anaerobically" [1,
p250]. Release of lactic and pyruvic acids from
anaerobic metabolism led to further decrease in pH, to
as low as 6.60.
Myers stressed that anaerobic processes supply only
1/19 the energy that is generated by aerobic
metabolism; and, "Just as rapid decreases in oxygen
content lead to rapid deterioration in cardiovascular
function, so the sudden restoration of oxygen to the
blood stream during resuscitation leads to a dramatic
reversal in vital organ function" [1, p250]. Normal pH
levels returned to normal more slowly; and according
to Myers, "Herein lies the most convincing
demonstration of the importance of oxygen delivery
and of the minimal importance of the concentration of
the other acid-base and respiratory gas constituents
for the functioning of vital organs."
Oxygen is an urgent on-going need for all aerobic
species. We tend to take breathing for granted hence
forget to include oxygen as the most essential of
physiological needs; the need for warmth, food, and
shelter etc follow.
- Myers RE (1972) Two
patterns of perinatal brain
damage and their
conditions of occurrence.
Reference