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At 05:28 PM 9/6/00 -0700, Scott wrote:
>I knew there had to be a reason for telephone psychics!
>
>Hey, can you put the "oxygen window" into words that a Jarhead can
>understand and use for *normal* diving, as in 30 minutes or less of
>decompression? I have, at last count, 5 definitions of the concept, as it
>applies to decompression. I have spoken to no less than 4 experts, and they
>all have a different story, and none of them seems to float.

Basic one atmosphere oxygen window = the inherent unsaturation
That is, since metabolism burns oxygen and the "exhaust", namely CO2, is 
chemically transformed and taken out of solution and thus ceases to be gas 
tension there's always a total tissue tension of dissolved gases somewhat 
below the inspired P gas. That was a long sentence, let's try again: The 
lungs contain oxygen, inert gas and CO2 -- so does the blood. Since the 
body burns oxygen the oxygen drops. This makes the total gas tension in 
plasma and tissues a bit lower than what could have been dissolved. This 
"inherent unsaturation" leaves room for more gas to dissolve and promotes 
the shrinking of any bubbles that may be present.

The oxygen window in diving has an extended meaning. Since hemoglobin loads 
up with oxygen till it's 100% saturated and no more -- since tissue tension 
of extra oxygen is being metabolized and thus being checked -- since excess 
oxygen will be burned off sooner or later anyway -- one may disregard the 
extra oxygen as gas loading. Put simply, breathing a high PO2 (or rather, 
low P inert gas) provides "more room" for dissolved inert gas and promotes 
redissolving and elimination of any inert gas bubbles present. If you're at 
20' breathing oxygen you're making almost 1.6 ATA of free space for keeping 
inert gas dissolved while if you were breathing air 79% of that space would 
be occupied.

Extra space for keeping gas in solution means it won't have to be present 
as bubbles and bubbles are known to be bad for you :-)

regards,

Hans

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