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>> function in an animal model. My research has shown even very small amounts
>> of air in the brain can alter blood flow and function. Larger amounts are
>> very bad, and none of this is due to bubbles blocking blood vessels. I want
>Are you saying that even relatively small amounts of gas in the blood, as
>in a minor type I hit, causes brain damage?
Yes
>Is the damage permanant?
I guess you mean is it permanent in people, or maybe you mean are there any
cognitive deficits associated with diving? I wish I had a way of finding
out. (Actually there is a way, but I don't have access to the resources I
need to do it). The brain is better at repairing itself than we used to
think and can compenstate for a lot of minor and even major damage.
>any type of DCS symptom to be evident, there must be a significnt amount of
>gas in the blood so "relatively small" is far more than insignificant.
Relative to the amount of gas you might expect is needed to cause any
damage. In my rabbit model of cerebral arterial gas embolism (read DCI) 25
microlitres of air injected into the internal carotid artery is enough to
reduce brain blood flow and brain function by up to 50% over 3 hours. To
see these air emboli it is necessary to videotape the blood vessels on the
surface of the brain and play the tape back a slow speed to see the bubbles.
I would describe 25 microlitres of air as 'relatively small'.
>In Bove's book "Dive Medicine", the chapeter on DCS (not written by Bove)
>states that it is suspected that cerebral damage from DCS is far more
common >than is currently realized.
I agree.
>If damage is not caused by bubbles blocking blood flow, what does cause damage?
It is caused by biochemical processes initiated either by the presence of
gas in the circulation and/or the effects of gas emboli passing through the
circulation. The most important culprits here are the granulocytes. These
further reduce brain blood flow and go about the place wrecking things.
Have a nice day.
/Rat
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shelps@ac*.ma*.ad*.ed*.au* Stephen Helps
Anaesthesia & Intensive Care
University of Adelaide
ADELAIDE, 5005, South Australia
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If everything seems to be going well, you've probably overlooked something
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