Mailing List Archive Mailing List Archive
On Sat, 16 Sep 1995, Bernie Woolfrey wrote: > George, well, i are is not george....but i know what he means.... > What do you mean by "Oxygen Window"? it was once remarked that the only saturated diver is a dead diver (hills '77). the partial pressures of gasses dissolved in the tissues of a living diver sum to less than the pressure of inspired gas. this difference in pressure is the O2 window (or inherent unsaturation, etc), resulting from the metabolic exchange of O2 for CO2. CO2 is highly soluble in tissues, so its tension is low for a given concentration. that is, the partial pressure of CO2 doesn't make up for the ppO2 used in a breathing cycle. obviously, what Hills meant was that if there is no metabolism, then the O2 window is zero. the O2 window is of vital importance to bubble model decompressions and for IWR.for example, consider if you have formed bubbles and you recompress yourself. the pressure inside bubbles in your body increases with ambient. if you breath O2, your tissue tensions of inert gasses will continue to fall. now, if the pressure of inert gas in the bubbles exceeds the tissue tension (this excess is the O2 window....), gas will diffuse from the bubble to the tissue, and then hopefully out to circulation. there are two ways to open the O2 window: increase fO2 (within ppO2 tox limits....) or increase depth. the O2 window is the primary reason why stops should be pulled deep to eliminate bubbles.it is also an excellent reason for not blowing off DEEP stops (within 2ata of bottom depth....). if bubbles are eliminated early in the ascent, they won't be around to grow during your shallow stops or on the surface. now with regards to playing the O2 window off of oxtox, there have been reports of much lower cns thresholds for mixed gas compared to pure O2 . i don't know whether this was due to work-of-breathing (co2 generation/retention) at depth or if this is fundamental physiology.... in summary, there is no reason to open the window too wide early in the ascent if it's going to be slammed shut by an O2 hit--after all none of us want to be saturated divers. an excellent review of the O2 window was given by vann and thalmann in bennett and elliot #4,chpt. 14. regards, em. _____________________________________________________________.sig Eric Maiken email: eapg243@ea*.oa*.uc*.ed* Dept. of Physics o: 714 824-6621 U of California fax: 714 824 2175 Irvine, CA 92715-4575
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]