Diving 32% Nitrox with "Air" Algorithms

[dmaziuk]

This is exactly the concept I was referring to: under medical control, high oxygen pressure is a great and powerful tool, exactly as a drug.

Well, not exactly: this is about the theory of aging, ROS, "eliminating all free radicals", etc. Of course none of those studies have anything about how much and for how long to do it to get the apparent antioxidant boost... or how much is too much. FWIW I haven't even bothered getting a nitrox cert, myself: I'll pay for it if and when I feel like I need it, but so far I have not felt that way.

 

[scubadada]

I was on a 10 Day trip on a live aboard in Turks and Caicos. Diving 5 dives a day and the top of the reef was 40 feet or lower. Using an Oceanic Datapro 3 computer. On several dives towards the last half of the trip found my O2 level were in the warning level and having to stay higher in the water column.

Dive computers use 2 major mechanisms for tracking O2 exposure, both based on the NOAA O2 exposure table. I dive a Shearwater Teric and an Oceanic VT3, illustrating the 2 methods.

NOAA O2 exposure table and section on CNS O2 toxicity from the Teric owne's manual

Shearwater computers use O2 exposures from the NOAA table and then apply a 90 minute half life to the elimination of O2 during surface intervals. Using this method, recreational divers will not approach the O2 exposure limit. My highest CNS O2 exposure has been 44%, following 4 dives in a day on 36% nitrox at average depths of 56-68 feet for 53-56 minutes.

Section on O2 toxicity from the VT3 owner's manual

Oceanic, and perhaps other Pelagic Pressure Systems computers do not apply a 90 min O2 elimination half life. Instead, they use cliff vesting for O2 elimination 24 hours after the end of the dive. This allows for 5 (or more) dives within a 24 hour interval when diving continuously over days. I did a 5th dive the next morning afer the 4 dives listed above using 34% nitrox for 70 min at an avg depth of 64 feet. My Teric showed an CNS O2 exposure 0f 23%, starting at zero that morning. My VT3 exceeded 100% exposure for the 24 hour period. My VT3 is frequently in warning or violation when I am diving continuously on higher nitrox mixes in SE Florida.

I have been aware of the 2 methods for tracking O2 for many years and have posted about them previously Alternate Gas Backup Computer. I take this into consideration when interpreting the information from my computers.

 

[SysGreg]

Most modern computers track CNS%. Few computers (if any) track OTUs; Shearwaters, for example, do not.

Garmin does track OTU.

 

[kammel78]

Are we operating under the assumption that the NOAA tables are anything close to being accurate?

 

[scubadada]

Are we operating under the assumption that the NOAA tables are anything close to being accurate?

It's what we all use, perhaps someone can comment on their derivation. You can ask the same about decompression algorithms.

 

[inquis]

Are we operating under the assumption that the NOAA tables are anything close to being accurate?

I think most do, simply because they are not in a position to develop and/or characterize a better approach. "Accurate" may be a bit of a misnomer as well, as those tables are upper bounds thought to have broad applicability. Individual variation will always exist, hopefully on the safe side of those guidelines.

 

[kammel78]

It's what we all use, perhaps someone can comment on their derivation. You can ask the same about decompression algorithms.

I think if you look into the origins of that table, you'll be surprised. Also, if you calculate the OTUs on any decent sized ccr dive, you'd also be surprised.

At least with decompression algorithms, there's been a long history of alternatives, revisions, open debate...

The OTU tracking...it's conservative enough that people aren't getting hurt, which is a valid outcome, but is it any way accurate?

 

[formernuke]

Also, if you calculate the OTUs on any decent sized ccr dive, you'd also be surprised.

We did in my class, I was surprised.

 

[inquis]

Dive computers use 2 major mechanisms for tracking O2 exposure, both based on the NOAA O2 exposure table.

Tracking OTUs (a.k.a., the REPEX approach) is a third major approach. However, someone staying within the "Maximum per 24 Hr" limits in the above table winds up approximately satisfying the 300 OTU daily limit as well.

(Using the 24 hr times, the accumulated OTUs would be 289 (1.6 PO2), 306 (1.55 PO2), 321 (1.5 PO2), etc., but all hovering around 300. As such, I doubt those 24 hr times were based on OTUs. In fact, I suspect the long-term OTU limit may have came from the 24 hr times, with additional allowance given for shorter missions.)

 

[Angelo Farina]

Well, not exactly: this is about the theory of aging, ROS, "eliminating all free radicals", etc. Of course none of those studies have anything about how much and for how long to do it to get the apparent antioxidant boost... or how much is too much. FWIW I haven't even bothered getting a nitrox cert, myself: I'll pay for it if and when I feel like I need it, but so far I have not felt that way.

My son is a genetics researcher at the University of Milano-Bicocca, doing a PhD on cellular aging, and working at the research unit in San Raffaele Hospital (San Raffaele Telethon Institute for Gene Therapy - SR-Tiget).

https://en.unimib.it/giacomo-farina

San Raffaele Telethon Institute for Gene Therapy - HSR Research

In his lab they tested most of these new theories about using oxygen, ultrasound, green light, pulsating magnetic fields, etc...

His opinion is that all these are actions with some biological effects, but for assessing the capability of "rejuvenating" cells there is still a long way to go.
Instead the immediate harsh effect of these actions, triggering inflammation, are real and easily measured. The basic idea behind all these approaches is the same as behind the skin treatment of "peeling", or the like. You stress the cells, and force a part of them to die, so new cells replace them. Or stressing the cells triggers self-repairing procedures.
As said, I have no objection about this kind of treatment, if performed under medical control and for getting a benefit.
I would never expose my body to these types of cellular stress for no reason and outside medical advice.