Oxygen Toxicity and Bends

[mjsylver]

Which is why I will always stick to recreational limits on geezer gas.

 

[descent]

... I was tested for [oxygen toxicity] by the U.S. Naval School for Underwater Swimmers. They took as to 66 fsw in a chamber and had us breath pure oxygen for a time (5 or 10 minutes--can't remember which), to see if we experienced symptoms.

[-]The Navy OTT is one half hour at a pp02 of 2.8[/-]. The Navy OTT was one half hour at a pp02 of 2.8.

If you twitch[ed], they kick[ed] you out of dive school and ban[ned] you from diving. (pdf)

 

[Superlyte27]

The Navy OTT is one half hour at a pp02 of 2.8.

If you twitch, they kick you out of dive school and ban you from diving. (pdf)

It's pretty rare. I performed this test 30 times a month for 6 months to new students at commercial dive school. In 180 students, no one every tox'd

 

[descent]

It's pretty rare. I performed this test 30 times a month for 6 months to new students at commercial dive school. In 180 students, no one every tox'd

In the linked paper, the two researchers guesstimate from their limited data that the rate of heightened sensitivity in their test population is 26/1347, or 1.93%.

But they also admit that they suspect a great deal of underreporting. It is likely that some operational divers are being exposed to elevated partial pressures of O2 and not experiencing serious symptoms. If so, then the two percent number sounds far too high.

 

[dreamdive]

I was under the impression that tolerance testing is no longer done since there is a lot of intra-variabilty (same person may tox sooner/later than previously).

What will be interesting to watch-out for is Dr. Whelan's study, looking to increase tolerance to oxygen via induced ketosis: Oxygen Toxicity: Potential New Method of Prevention

Add Helium - The Rebreather Epicenter

 

[Superlyte27]

It's not done anymore. You are correct.

 

[Kevrumbo]

. . .Was very worried about OxTox seizures while breathing Open Circuit Oxygen at 9meters depth for over an hour (an Oxygen ppO2 of approx 2.0) during an In-Water-Recompression (IWR) session last Oct-Nov 2014, even with interval relieving Air Break gas switches.

Also the previous three type I DCS incidents experienced on my Truk trip last Oct-Nov 2014 -all were upper Right arm/Shoulder classical acute "pulsing" symptoms with increasing pain within 90min time post-dive, and occurring within three to four days of starting Open Circuit Deep Air bottom mix dives with 50% & O2 deco (two tech deco dives per day with a 3 hour SIT). Possible contributing factors were dehydration, insufficient "acclimatization" to the tropical environment, and no prior "work-up" practice deco dives to sensitize the body's immune/inflammatory response system to high FN2 saturation & resultant micro-bubbles in tissues & venous blood vessels (first early AM deep dive with deco of that trip was SF Maru at 51m ave depth, 45min BT and over two-and-a-half hours runtime, after trans-pacific flight from LA arriving late in the night before).

All DCS Pain Symptoms at that time last Oct-Nov were resolved with IWR -the modified Australian Method as taught by UTD- with either 30, 60 or 90min of elective O2 breathing at 9m depth (10min O2:with 5min Air Break); and then slow 0.1m/min ascent to surface (same breathing 10min O2:with 5min Air Break). Went with 60 minutes O2 time at 9m (Air Breaks do not count or accrue credit into the O2 time at 9m; on the slow 0.1m/min ascent you have to hold at depth during the 5min Air Break, so after 10 minutes and 1 meter delta of ascent on O2 you switch to Air and stay at that depth for 5 minutes). The entire IWR treatment session took three-and-a-half hours (and the CNS readout on the Petrel Dive Computer was "pegged" at 999).

-------
There's also this interesting prelimInary Study:


Aviation Space Environ Medicine 2015 Jan;86(1):41-5. doi: 10.3357/AMHP.4113.2015.

End Tidal CO2 in Recreational Rebreather Divers on Surfacing After Decompression Dives.

Mitchell SJ¹, Mesley P, Hannam JA.
Author information

• ¹Department of Anaesthesiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand.

Abstract

INTRODUCTION:

Deep dives using rebreather devices result in oxygen exposures that carry a risk of cerebral oxygen toxicity. Elevation of arterial CO2 levels increases this risk. CO2 retention may occur during the deep working phases of dives, but it has not been investigated in 'real world' dives at the end of resting decompression when oxygen exposures are peaking, often to levels higher than recommended maxima.

METHODS:

We conducted an observational field study to measure end tidal CO2 (Petco2) in divers surfacing after decompression. Sixteen rebreather divers conducted two dives and two completed one dive (a total of 34 dives) to depths ranging from 44-55 msw. Bottom times ranged from 35 to 56 min and time spent on decompression ranged from 40 to 92 min. The first breaths on reaching the surface after removing the rebreather mouthpiece were taken through a portable capnograph. The Petco2 was recorded for the first breath that produced a clean capnography trace. Petco2 measurement was repeated for each subject 2-3 h after diving to give paired observations.

RESULTS:

There were no differences between mean surfacing Petco2 [36.8 mmHg (SD 3.0)] and the mean Petco2 made later after diving [36.9 mmHg (SD 4.0)]. One subject on one dive returned a surfacing Petco2 higher than a nominal upper limit of 45 mmHg.

DISCUSSION:

We found no general tendency to CO2 retention during decompression. It is plausible that breaching oxygen exposure limits during resting decompression is less hazardous than equivalent breaches when exercising at deep depths. Mitchell SJ, Mesley P, Hannam JA. End tidal CO2 in recreational rebreather divers on surfacing after decompression dives. Aerosp Med Hum Perform. 2015; 86(1):41-45

 

[descent]

It's not done anymore. You are correct.

Well, ffs. No one told me.

Screening for oxygen sensitivity in U.S. Navy combat swimmers.

"The United States Naval Special Warfare Community uses oxygen tolerance testing to screen Navy combat swimmer candidates .... The authors conclude that O2 tolerance testing of U. S. Navy SEAL candidates is not a useful screening test and recommend discontinuation of this test."

Naval Medical Center, San Diego, California 92134-5000, USA
Undersea Hyperbaric Medicine. 2000 Spring; 27(1):21-6.​

Fifteen years ago?

Is this what it feels like to get old?

 

[Superlyte27]

Seems right. I was doing it in 1999

 

[ajduplessis]

Never toxed and hope it never happens. I completed a schedule 6 treatment a year ago and never experienced any symptoms. Those who have toxed mostly all mention visual challenges.

I use high volumes of vitamin C & E before, during and after all big dives. Does it actual help or is it placebo?