Diving after DCS

[tursiops]

If what you write is true then PO2 settings and MOD tables for a particular EANx blend are irrelevant. Which of course, is not the case.

You are conflating O2 exposure with O2 toxicity (hence MOD). Two different things. You can have one without the other.

 

[Maolli]

You are conflating O2 exposure with O2 toxicity (hence MOD). Two different things. You can have one without the other.

Yes you can have O2 exposure without O2 toxicity but you cannot get O2 toxicity without exposure to 02.

At least theoretically excessive 02 exposure can cause O2 toxicity in single tank recreational divers breathing Nitrix blends of 40% or less although this has never been proven to have occurred.

 

[dmaziuk]

Not knowing how much conservatism is needed plagues the "pretend it's air" approach as well. Perhaps on 36% they're unlikely to have an issue, but on 28% they might. The risk clearly increases, which was the main point I was trying to make.

The part you're missing is that the M-values, 99 Surfing GrapeFruits, and the rest of the computer conservatism tweaks, normally apply to the leading tissue compartment. Nitrox applies to all TCs. You don't know how much conservatism you need on EAN28, but you do know that you get reduced nitrogen loading across the board and not just in the bit that happens to be controlling at the moment depending on the profile, prior bubble voodoo, heart rate, and whatever else your computer may be "factoring in".

Also, I'm not digging up the references but IIRC when you get to the actual statistics, it disappears at GF of 60-ish or thereabouts. So mathematically, setting your GF to 60 does not mean you won't get bent, it means we'll have no clue what your chances are.</nitpick>

 

[Maolli]

You are not paying attention. These divers are 60ft two dives a day. So MOD and PO2 are not relevant.

You are not reading what you posted. You stated that 02 exposure is irrelevant to recreational divers. Period.

"O2 exposure for recreational open circuit divers has absolutely ZERO value." -davehicks

 

[hiker11]

I disagree. We often recommend that divers in the OP's husband's situation dive nitrox on the air setting on the computer.

The OP reported that her husband already had a PFO test.

What you described sounds like inner ear decompression sickness. We would typically recommend a PFO test in your husband's case just to have some data on which to base a diving recommendation, as was done here. Can you say exactly what test he had? Was it a transthoracic echo? If so, was bubble contrast used, and did they have him perform a Valsalva (bear down as if having a BM) maneuver during the test? Also, what did the skin bends look like? Did it have more of a marbled appearance, or was it red and blotchy like hives?

IF he has a PFO, we would generally recommend that he stop diving after an incident of severe DCS. That's not acceptable to some divers, so our recommendation in those cases is usually to do exactly what you all are doing, which is dive more conservatively, use nitrox on the air setting of your computer, take a day off in the middle of the dive trip, limit your dives to two per day, not push the computer to the edge of the no-stop limits regardless of setting, and avoid provocative dives (generally those deeper than 60 feet). You'll have to gauge the risk of taking dive trips in remote locations and mitiage it as best you can. My other recommendation would be to get evaluated by a physician trained and experienced in assessing divers, which you've already done.

Best regards,
DDM

Thank you for your helpful comments.

The test my husband had was a Transthoracic Echocardiogram. Quoted from the report: "An agitated saline study (bubble study) was performed with and without Valsalva, and was inconclusive in determining if a small shunt (PFO) is present."

My husband remembers only 1 skin bends episode, but I think there may have been another. This is all in retrospect-- if we had known about skin bends at the time, we would not have brushed it off. We just thought something was odd. He doesn't remember any rash, but just a weird skin feeling on his abdomen a few hours after diving.

Both physicians he saw checked the computer profiles from his dives in Cozumel and nothing was an obvious cause of the DCS. The thing that was different on that trip was that we were diving with a company that gave us big tanks, so our dives were longer than usual. There were also big currents that week so every dive was more strenuous than usual and some days it was really ripping current.

We thought our diving days were over when he got the recent DCS hit in Cozumel. But when we asked the hyperbaric physician in Coz if he could ever dive again, he answered enthusiastically "Absolutely!". He characterized the DCS hit as 'mild'. We had a dive boat trip for the Galapagos booked and asked him about it. He didn't see any problem with my husband going but advised diving very conservatively. In the end, we decided to cancel the trip since we thought it might be too risky.

At my husband's age of 73, we didn't think we had enough years of diving ahead to justify the more invasive PFO test and subsequent PFO closure if one was found. Cost is not at issue at all-- it was more about the procedure and surgery risks weighed against the risk of diving super conservatively. Both dive physicians have been very supportive of my husband continuing to dive or we would not even consider it. But obviously, we are still trying to figure out the way forward.

 

[hiker11]

What computer does he use? At one time it was not unusual for some divers to set computers to air when diving nitrox (while limiting depth to the actual MOD) to give a more conservative profile. But there are now computers with conservative algorithms as well as additional settings for added conservatism.

If surgery is out and it will make no difference in your choices I agree, there is no reason to do the additional testing.

Shearwater computer. Now being set to a conservative profile.

 

[davehicks]

You are not reading what you posted. You stated that 02 exposure is irrelevant to recreational divers. Period.

"O2 exposure for recreational open circuit divers has absolutely ZERO value." -davehicks

It isn't. CNS O2 exposure is not relevant to recreational open circuit divers. It is next to impossible to come anywhere close to a significant level of exposure. In the context of 60ft 2 dives a day: impossible. So not relevant.

Ps: PPO2 is a real time measure and not cumulative. It's a different topic.

 

[tursiops]

Shearwater computer. Now being set to a conservative profile.

What was it set on before?

 

[lizardland]

You are not reading what you posted. You stated that 02 exposure is irrelevant to recreational divers. Period.

"O2 exposure for recreational open circuit divers has absolutely ZERO value." -davehicks

He's right. Recreational divers diving open-circuit nitrox within the limits of their training will be extremely unlikely to come near the cumulative CNS oxygen expsoure limits that more technical computers track.

I've had mild symptoms of pulmonary toxicity from multiple days of long rebreather dives but I'd be surprised if that was possible on single cylinder recreational diving unless you were doing a hell of a lot of dives. In which case lung irritation is probably the least of your worries.

 

[Maolli]

He's right. Recreational divers diving open-circuit nitrox within the limits of their training will be extremely unlikely to come near the cumulative CNS oxygen expsoure limits that more technical computers track.

He said monitoring O2 exposure in rec divers has zero value = irrelevant. Not the same as "unlikely".