Nitrox o2 question......

[gbrandon]

Since taking my nitrox course, i have a few questions that the instructor couldnt answer. Maybe someone here can help me out?

1) some of the conditions that are predisposers of oxygen toxicity are: people that retain co2, using steroids, amphetamines, excessive caffeine. On the opposite end, vitamin e and magnisium were thought to have reduce the likelyhood of getting oxygen toxicity. My question is, what is meant by retaining co2? How does you body retain co2 versus someone that doesent? Have there been any tests done to see what the thresholds were on a person that had predisposers in one test, and used non-predisposers (<---is that a word?) in another test? How much credance do you give the above statement regarding predisposers?

2) Are there any studies that have been done to be able to test a person to see what his threshold is? how do you decrease your odds? (besides using the above as guidelines) Does repeated exposure to high levels of oxygen (over 1.0 ata) increase your tolerance?

thanks in advance.........

 

[roakey]

The only studies I can remember being done that identified CO2 retainers was attempting to predict who will get altitude sickness. This is reaching waaaay back, but it wasn't a very good study as far as I can recall in that it took a person's pet theory (CO2 retaining predisposes one to altitude sickness), rejected some people from the climb because it was determined that they were CO2 retainers (and they were NOT later tested to see if they would actually suffer from altitude sickness) and of the people who "passed" one still got altitude sickness.

Which doesn't tell you much except that there must be a way to test for it, but the study wasn't clear on those details.

Be conservative on your PPO2s and don't worry about it. Just because the working PPO2 is traditionally 1.4ATA, there's no need to dive exactly at 1.4ATA all the time...

Roak

 

[pipedope]

All of the literature I have seen indicates that O2 tolerence changes so much from day to day and even dive to dive that testing beforehand is useless.

 

[rmediver2002]

The military used to conduct ppo2 testing as a pre-qualification for dive school, as already stated the threshhold was shown to vary so widely from day to day for a given individual that the test was abandoned.

There are many variables to reactions to o2 toxicity and that is the reasoning behind selecting such low partial pressure threshholds (1.4 or 1.6 depending on agency) for SCUBA / NITROX diving.

Jeff Lane

 

[Dr Deco]

Dear gbrandon:

Oxygen Toxicity Sensitivity

There are more unknowns than knowns in this equation. There have been a number of studies over the past decades dating back to prior to WW II. The final result in all of these was that the partial pressure for oxygen seizure varied not only from individual but also within a given individual. There appeared to be no way to determine where you might get a seizure or not unless you were below a definite threshold. There is a point below which an individual will not encounter CNS (or pulmonary) toxicity. These are the partial pressure limits that all divers are advised to follow.

Carbon Dioxide Retention

It was noted that some individuals do not eliminate carbon dioxide from the lungs, and thus arterial blood, as well as do others. This carbon dioxide “retention” thus refers to lungs. The general explanation that follows is that this carbon dioxide increases the blood flow to the brain and increases oxygen partial pressure beyond the needs of the CNS. This excess results in an increase in “reactive oxygen intermediates” and triggers the seizure. There are no reliable methods currently to beat this problem.

Training

It is the experience of decades that you cannot develop and resistance to oxygen toxicity by repeatedly breathing increased partial pressures. It would most likely be detrimental in the long run. :boom:

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[gbrandon]

Dr Deco once bubbled...
Dear gbrandon:

Carbon Dioxide Retention

It was noted that some individuals do not eliminate carbon dioxide from the lungs, and thus arterial blood, as well as do others. This carbon dioxide “retention” thus refers to lungs. The general explanation that follows is that this carbon dioxide increases the blood flow to the brain and increases oxygen partial pressure beyond the needs of the CNS. This excess results in an increase in “reactive oxygen intermediates” and triggers the seizure. There are no reliable methods currently to beat this problem.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

How does one know if he/she has a problem with carbon dioxide retention? Is there a test for that?

Im more curious than anything. I dont drink caffeine, and dont smoke, work out daily, etc, so I dont feel im in any big danger, even if I did reach my maximum ppo. I was just more interested in the background of it all.

Thanks for the reply.

 

[blacknet]

Hello,

Basicaly everyone has a 'problem' with co2 retention, the question is how much work needs to be performed to get into the unsafe limits and how good the ventilation equipment is.

What's interesting to note is bennett and elliot states "Individuals who tend to retain CO2 durring exercise are found occasionally in the general population of atheletic young men, but the proportion among EDU divers was extraordinarily high." They also note higher levels amount ex-divers.

Ed