How to measure sensitivity to oxygen

[mdax]

Cora and i have both been tested for PFO's through our local doctors.
We're wondering how to test for sensitivity to oxygen, either duration or ppo2 exposure as it seems to be something that is difficult to determine but will kill you quickly in a cave.

Has anyone outside a military member requested a test using a chamber and o2 for periods of time to determine whether you have elevated sensitivity?

What type of test does the military put candidates through? depth/time and ppo2.

It'd be interesting dealing with our HMO regarding approval for this test but they've always been really good about our other requests...
Thanks

[Sharky1948]

From what I understand, a test of O2 sensitivity would be of little value. The body's sensitivity to elevated PO2 varies from dive to dive, day to day, etc. I'm not sure you would learn anything valuable even if such a test were available to you.

[Greenwood_60]

I think you would be better off being concerned that you might be sensitive, than "knowing" you are not.

[adam0321]

There used to be what's called aott. Or oxygen toxicity test for all seal and recon marines. What we did was put divers in a chamber at 60 feet and put them on oxygen. I believe the time was around 20-40 minutes. This was stoped because it was implemented at the end of training and of someone failed it was 2 years of training wasted. And I think only about 2% actually had problems.

Sent from my Eris

[gasdiver]

There used to be what's called aott. Or oxygen toxicity test for all seal and recon marines. What we did was put divers in a chamber at 60 feet and put them on oxygen. I believe the time was around 20-40 minutes. This was stoped because it was implemented at the end of training and of someone failed it was 2 years of training wasted. And I think only about 2% actually had problems.

Sent from my Eris

When I went through commercial diving school in 1980, we did a PO2 test in the can at 60' for 30 min. I never heard of anyone failing the test, but it was given about 30 days into the 5 month program. I guess if you failed, they'd refund some of your money. During my 4 years working in the Gulf, I never saw anyone get an O2 hit in the water or in the can. I have no idea if the commercial diving schools still do this.

[FW]

When I went through commercial diving school in 1980, we did a PO2 test in the can at 60' for 30 min. I never heard of anyone failing the test, but it was given about 30 days into the 5 month program. I guess if you failed, they'd refund some of your money. During my 4 years working in the Gulf, I never saw anyone get an O2 hit in the water or in the can. I have no idea if the commercial diving schools still do this.

Herein lies the problem. We used data similar to this back in the '70s and determined that 50' would be safe for O2. Then Lewis Holtzendorff toxed on O2 at 50'. We adjusted the depth several times over the next 40 years as more accidents happened (not all in caves), to the current 20'. The bottom line, NO TEST in a chamber will tell you how you will react in the water.

[Kelly Jessop]

. The bottom line, NO TEST in a chamber will tell you how you will react in the water.

That is what I understand,why this paradox exists,but people can breathe ppo2 of 2.5 of oxygen at rest in a chamber at rest and be fine,and replicate the same thing in the water,and show symptoms.

[karst.window]

Unfortunately there just isn't any way to definitively test your sensitivity to oxygen. Most of current "wisdom" is based on anecdotal evidence as has already been mentioned. I do recall however going back through most of the "toxicity" accidents when I was going through my cave as well as rebreather training and did not find any events (even counting multi-day dive profiles) that were reported with pO2's below the 1.2 threshold, however nearly 100% of seizures underwater will be fatal. (Someone feel free to correct me if they find evidence to the contrary as I may find myself diving a 1.0 as Ken does.) With the stakes that high it seems to be prudent to lower your pO2's for the working portion of the dive to 1.2 as increasing even to 1.4 offers marginal benefit.

As far as nitrogen being "anesthetic" and or "narcotic"...

We have all experienced the affect of nitrogen "narcosis". There does appear to be some type of affect with regards to impairment of motor function, motivation , and judgement. How this actually occurs is largely unknown. Hell we still don't even know for sure how many modern anesthetics exert their effects. General anesthetic gases as well as IV anesthetics will prevent as well as "break" a seizure very rapidly. I would expect nitrogen to play a minimal role in the concentrations our bodies see to prevent or attenuate a seizure.
With Hal Watts I would say that on certain days when he felt the narcosis more so than others is probably based on descent rate. The faster he descends, the more rapid the increase in the "dose" of nitrogen he received. For instance, if I have an entire vial of Diprivan which is an IV anesthetic (Michael Jackson Juice), I can give that entire vial to a patient and they will remain "awake". They will be impaired but observers would describe them as awake. Liken that to a slow descent. Now I take that same vial of Diprivan and I give the whole thing in one push then unconsciousness will ensue. That would be more of the rapid descent type. Rapidly increasing the dose of an "anesthetic" or "narcotic" drug will increase its onset and side effects. Basic pharmocology.

I expect the answer to oxygen sensitivity lies in consideration of many different mechanisms but a large part of it in my opinion is based on acute (single dive very high pO2) and chronic exposure (multi day diving). Not to mention oxygen free radical scavenging which likely plays a role as well. With so much individual variation from a physiologic standpoint as well as from a dive practice standpoint we may not ever get to the bottom of it. Way too much physiology to discuss on this forum but again it seems prudent to me to lower working pO2's because no one wants to find out how sensitive they are to oxygen the old fashioned way.

Sean Costabile, MD
Cardiovascular Anesthesiologist

[gasdiver]

The bottom line, NO TEST in a chamber will tell you how you will react in the water.

I agree.

[Ken Hill]

FWIW, a former student who is a long practicing MD specializing in Hyperbaric Medicine and and active (non cave) diver told me a while ago he believes there is an anesthetic affect of the PN2 (Nitrogen Partial Pressure) that may reduce the toxicity effect in water. I'd like to hear other opinions as to this theory of his. It may go a long way to explaining the causes of in water incident that may or may not have been seizures that can be attributed to P02.

His theory was based on early diving to depths in the 260 - 300 ffw range on air and long exposures to P02 of 1.8- 2.1 that either rarely produced or produced no evidence of what appears to be toxicity issues. Yet, I've interviewed two people that took 80% and the other 100% to greater than four atmospheres for less than a couple of minutes and both stated they felt physical symptoms that alerted them to the mistake.