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rearing up (long)



List:
Please allow me to try my hand at answering some of these interesting
topics with my usual disclaimer that my vertebrate knowledge is almost
entirely confined to humans.
1.  In terms of Betty Cunningham's remarks about whales, before diving
cetaceans expell air from their lungs and use oxygen attached to
hemoglobin and myoglobin during the dive.  If oxygen were exhanged in
the lung during the dive, nitrogen would dissolve in the blood, and
bubble and cause distress on the ascent.  While diving, arterial shunts
maintain normal blood flow to the brain and reduce it to the muscles; a
slowing of the heartbeat further economizes oxygen use.  As has been
mentioned, the hydrostatic pressure encountered at great depths are
allieved by filling the body tissues with noncompressible fluids.
Alveolar collapse is complete in bottle-nose dolphins at 70 m. depth.
2.  The term "aneurism" has not been used correctly on the list.  A
cerebral aneurism is a dilatation (or ballooning) of the junction of the
arteries at the base of the brain, and may or may not rupture and bleed
into the subarachnoid space (and potentially be fatal).  They occur in
about 3 to 4 percent of the general public, and one study showed about
35% will bleed over a 15 year period.  They are NOT generally associated
with high blood pressure, and rupture occurs most commonly in young and
middle-aged adults.  Bill Berry of the group REM had one bleed a few
years ago.  The "aneurism" that is being used on the list should really
be called an intracerebral hemorrhage.  These are spontaneous ruptures
of small penetrating  arteries deep in the brain and ARE associated with
hypertension (high blood pressure).  When one bleeds it is called a
stroke.
3.  In terms of the sauropod rearing question, with their small brains
and presumably small-diametered cerebral arteries I have been under the
impression they would not require that much of an increase in blood
pressure to perfuse their brains.  I believe I heard somewhere that
turtles can function for quite some time with their cerebral circulation
entirely disrupted (was it a Bob Bakker quote?).  Would not a rearing
sauropod be able to increase her cerebral blood flow by increasing the
heart rate slightly, asking the adrenals to kick out a little more
cortisol and adrenaline, and increase the sympathetic nervous system's
firing to the peripheral arteries and veins thereby shunting blood to
where it's needed most, without raising intracranial pressures to
dangerous levels?  I believe so.
4.  Lastly, if sauropods weren't eating the trees, who was?
Sorry for the long note.--Ken Clay, M.D.