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>Prime Rat writes:
>> Blocking of brain arterioles or capillaries by bubbles produced during 
>> decompression or directly injected into the arterial circulation is only 
>> seen when the heart stops beating, ie (as is well known) after death.  If we 
>> perform a craniotomy on a rabbit and produce intra-artial bubbling by 
>> decompression or direct injection of air into the arterial circulation the 
>> bubbles are seen to pass though the arterioles and disappear.  They can in 
>> fact, be detected in the saggital sinus (using ultrasonic Doppler) exiting 
>> the brain vascular bed.  Conclusion?  Bubbles do not block the capillaries.  

>Can you provide a little more detail here.  I'm not clear after
>several readings of this how you conclude that bubbles do not block
>the capillaries.  

They are not seen to.  Blood flow is not affected for at least 45 minutes 
after the bubbles have been seen to enter the brain circulation.

>If they don't block the capillaries, what do they block?  Why wouldn't

They block nothing.

>they block the capillaries, if they block the lungs?  (Later in this
>message, you say "...the lungs can fill up [with bubbles]") Perhaps
>brain capillaries behave differently than other capillaries?

Pulmonary artery pressure is very low.  The bubbles stop in the lungs (up to 
a ceratin point) but they do not block lung 'blood flow'.  

>story@be*.wp*.sg*.co*		  Every dive is a decompression dive.

I've always thought that.

/rat

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
shelps@ac*.ma*.ad*.ed*.au*|Stephen Helps PhD            Ack!  ___/|
FAX   (08)232-3283             |Anaesthesia & Intensive Care       \O.o|
Voice (08)224-5495             |University of Adelaide            =(___)=
                               |ADELAIDE, 5005, South Australia      U
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"It's not denial. I'm just very selective about what I accept as reality."
                                         --- Calvin ("Calvin and Hobbes")
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