O2 before a dive?

[ams511]

u-2-spy-plane-evades-the-day-of-retirement: Personal Finance News from Yahoo! Finance

Above is a link from Yahoo about the U2. It seems that the pilots suffer from the bends on flights (probably from the pressure suits). Anyway the article states that as a precaution the pilots go on pure 02 an hour before the flight. Never heard of divers doing the same but it sounded interesting.

 

[H2O 70]

I'm sure that you would off gas a fair amount of N before the dive if you did this. The question would be then how much N would you on gas as soon as your started to dive, assuming your breathing gas has some amount of N in it. I would think that you would take up a lot N pretty quick because of the large gradient difference in the tissues.

 

[Bubbletrubble]

I would think that you would take up a lot N pretty quick because of the large gradient difference in the tissues.

I had thoughts along the same lines. The benefit of washing out nitrogen in your pre-dive prep could, theoretically, be lost at some point during the dive assuming that you were breathing a gas mix that contained a significant amount of nitrogen. Then, you'd be stuck off-gassing a comparable amount of nitrogen in the tissues...same as if you hadn't breathed pure O2 in your pre-dive prep.

Probably not worth the added expense and effort IMO.

On the other hand, breathing oxygen-enriched gas would make more sense during a safety/deco stop and post-dive to facilitate off-gassing of nitrogen that accumulated in the tissues during the dive.

 

[Diver0001]

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A ScubaBoard Staff Message...

Moved to the Dr. Deco foum as he has specific experience in this area

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[fppf]

The "Pressure suits" did not increase the pressure above 1 atm. What it did was prevent the pressure from dropping to a point where they would get bent and pass out in a 21% environment.

The reason they breathed O2 before a flight is the same reason tech divers use O2 at there last decompression stops. The U2 pilots (and astronauts doing EVAs) needed to decompress before gaining altitude (lower the pressure on there bodies) to avoid getting bent.

Pre breathing O2 before a dive wont make that much difference, you will on gas what you lost very quickly.

 

[Rhone Man]

But with pilots it is the other way around - they needs to get rid of their excess nitrogen before they fly, because it is after they ascend that they are at risk of bubble formation because of the lower partial pressures.

A diver going through off-gassing before they dive is just going to rack it back up again very quickly during the first few minutes of the dive.

 

[ams511]

Maybe I misread the article but it seems like they were getting bent when landing not taking off or during the flight. You would have thought the air force would have addressed the problem on an aircraft that has been flying since 1956.

 

[Guy Alcala]

The "Pressure suits" did not increase the pressure above 1 atm. What it did was prevent the pressure from dropping to a point where they would get bent and pass out in a 21% environment.

Well, the main reason for the use of pressure suits is to prevent your blood from boiling if the cockpit suddenly de-pressurizes, due to damage or an engine flameout that you can't get re-started before you descend to a safe height (bleed air from the engine provides the cockpit pressurization). The U-2 is essentially a powered glider, so it doesn't come down very fast. Nor is it very maneuverable, so changing direction (its velocity vector) quickly isn't an option, especially at its operational altitudes where the air is thin and control forces are weak.

IIRR the rule of thumb is that the boiling point of water drops 1 deg. C per every 1,000 feet, so at a height somewhere around 63,000 feet (depending on the atmospheric pressure and lapse rate that day) the boiling point of the water in your blood has dropped to body temp, 37 deg. C/98.6 deg. F.

Maybe I misread the article but it seems like they were getting bent when landing not taking off or during the flight. You would have thought the air force would have addressed the problem on an aircraft that has been flying since 1956.

Yes, you mis-understood, although the way it's written it's not clear. The pilot was suffering the effects of the bends incurred at altitude while he was landing, even though he had recompressed somewhat during the descent. It's as if he was a diver in a recompression chamber that hadn't yet re-pressurized him to (or beyond) his original depth, to force the bubbles back into solution.

Guy

 

[Dr Deco]

Oxygen prebreathe is of great value in altitude decompression, since you never add nitrogen afterwards.

Oxygen breathing for a diver is less efficatious, since you do breathe nitrogen later [as a part of the dive itself].

 

[JonKranhouse]

The French Navy published results of a normobaric pre-breathing study, in English, in 2009.

Olivier Castagna1, Emmanuel Gempp2 and Jean-Eric Blatteau2

(1) Institute of Naval Medicine, BP 610, 83800 Toulon Army, France
(2) French Navy Diving School, BP 311, 83800 Toulon Army, France
Accepted: 27 January 2009 Published online: 14 February 2009

Abstract
Oxygen pre-breathing is routinely employed as a protective measure to reduce the incidence of altitude decompression sickness in aviators and astronauts, but the effectiveness of normobaric oxygen before hyperbaric exposure has not been well explored.

The objective of this study was to evaluate the effect of 30-min normobaric oxygen (O2) breathing before diving upon bubble formation in recreational divers.

Twenty-one subjects (13 men and 8 women, mean age (SD) 33 ± 8 years) performed random repetitive open-sea dives (surface interval of 100 min) to 30 msw for 30 min with a 6-min stop at 3 msw under four experimental protocols: “air–air” (control), “O2–O2”, “O2–air” and “air–O2” where “O2” corresponds to a dive with oxygen pre-breathing and “air” a dive without oxygen administration. Post-dive venous gas emboli were examined by means of a precordial Doppler ultrasound.

The results showed decreased bubble scores in all dives where preoxygenation had taken place (p < 0.01). Oxygen pre-breathing before each dive (&#8220;O2&#8211;O2&#8221; condition) resulted in the highest reduction in bubble scores measured after the second dive compared to the control condition (&#8211;66%, p < 0.05). The &#8220;O2&#8211;air&#8221; and &#8220;air&#8211;O2 &#8220;conditions produced fewer circulating bubbles after the second dive than &#8220;air&#8211;air&#8221; condition (&#8211;47.3% and &#8211;52.2%, respectively, p < 0.05) but less bubbles were detected in &#8220;air&#8211;O2 &#8220;condition compared to &#8220;O2&#8211;air&#8221; (p < 0.05).

Conclusion:
Our findings provide evidence that normobaric oxygen pre-breathing decreases venous gas emboli formation with a prolonged protective effect over time. This procedure could therefore be beneficial for multi-day repetitive diving.
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Gundi, and any other industry insiders encouraging her litigation against ScubaBoard and 100 "Does," should save their money on lawyers. Quit trying to put ScubaBoard out of business, and pay to put oxygen concentrators on the livaboard boats she books in the Maldives -- that would generate positive PR. (Review / comparison of O2 concentrators by SPUMS in 2008)