Any reported cases of Ox Tox between 1.4 and 1.6?

[justinthedeeps]

Post in thread 'Scientific studies on air breaks' (check out post 21)

I want to Like this reply but is there a link people can click on?

 

[Kendall Raine]

That's my conclusion as a former USAF hyperbaric doc and retired cardiac anesthesiologist.
Sequential T6's are not wholly unlike 47 repeated sessions at a PPO2 of 1.2, or spending several days on a high PO2 ventilator with dehumidified gas. There's a tiny bit of oxidative stress on the lungs, plus the repeated dry gas exposure. My slight dry cough was indicative of that. I'll concede that the whole symptom complex may just have been alveolar dessication since my mouthpiece bypassed nasal humidification, but I personally think the high PPO2 played a small role. Symptom onset may have been sooner, but not noticed since we were so active. But arriving home and lying about, the slight cough became more noticeable.

@Duke Dive Medicine ?

Interesting. Thanks for the discussion. I guess the lung irritation from dry gas would have been true of any gas (e.g. air) with (maybe) some fractional additional contribution from the higher P02s. The corneal edema is interesting/suggestive and probably not dehumidified gas related.

I follow your observation that sequential T6's would not be wholly unlike 47 dives (average depth of 55 feet across ~12 days). Without accounting for SITs and overnight air breaks, 47 dives on 32% for 12 days would yield OTUs around 52.4 per dive/x4=210 OTUs per day x 12 = 2520 OTUs. This compares with five days of one T6 per day (584 OTUs x 5 = 2920). What I'm a bit confused by is that the REPEX 12 day daily limit is 300 per day/cumulative 12 day limit is 3600. The REPEX limits are designed to avoid whole body toxicity damage. I went through tech training in the early 90's when Hamilton was the "Man" and maybe thinking has changed on REPEX limits, but if they're still considered valid I wonder if much of what you experienced was related to factors other than diving EANx/chronic (whole body) 02 exposure (e.g. dry breathing gas, dry cabin air/flying, other). The corneal edema issue is a head scratcher.

I've done dive trips similar in 02 exposure to yours (12 days noD diving on 32%) and never had any visual or respiratory issues so am curious about this question of multi-dive/multi-day EANx exposure.

 

[rsingler]

Yeah, it's a head-scratcher. We can debate the cough, but my temporary (~10d) increase in astigmatism was real, persistent and disconcerting. But now it's gone. And I was reminded of my CCR training, where I noticed a shorter version of the same thing after repeated long dives and deco at 1.4-1.6.
Maybe I'm just getting old.
Or maybe as a retired doc, I'm just attuned to mild symptoms that others might dismiss, especially since they're gone in 10 days. For example, the astigmatism really only bothered me at night, when with dilated pupils my depth of field was reduced. During the day, with small pupils and longer focal distance, I was only rarely able to notice it.

As for debating the cough, anecdotally I have repeatedly done semiannual big trips with 40-50 dives over a short period, and don't recall this being an issue. The new wrinkle is having become CCR and tech certified in recent years, and pushing the PPO2 and duration envelope where I had shorter NDL dives before. Then again, I'm a decade older now. Who knows?

 

[Mobulai]

uints should be abolished from all „control“ software tbh, not like memory is such a bottleneck nowadays (or a really specific usecase)

Garmin dive computers have a design flaw where they store the CNS% as an unsigned 8-bit integer (uint8). I've seen mine hit 255% on a dive and wrap around back to 0%, which is kind of hilarious

Wait this is _still_ out there? Such an overflow surely must have been fixed already