Personal O2 Toxicity Concern question..

[Saturation]

Braunbehrens once bubbled...


Thank you for the information regarding hits and some of the mechanisms, I find this topic very interesting. I frequently deco on oxygen at 1.6 ppo2.

I am curious about some of the less intense effects of high ppo2. You mention free radicals and hydrogen ions, which I assume do some damage? I realize this may be on the order of breathing car exhaust or eating pesticides.

I assume there are also other effects, such as better oxygenation of areas in the body that may not "get enough" for some reason at a PO2 of .21

Also, I know some organisms are anaerobic, and exposing them to oxygen will kill them. Am I correct to assume that breathing high ppo2 gas will also have an effect on these?

Are there any other effects?

Hi B:

Quick comments as am about to leave to dive!

pp02 1.6 is ok for deco

Aging research suggests 02 exposure is damaging but is repaired whose efficiency diminishes with aging. At most, non-normal high 02 use may be associated with premature wear = early or accelerated aging. Among air divers, the long term effects of transient high pp02 show a definite reduction in vital capacity with time, i.e., a reduced lung elasticity.

If damage exceed repair, we have acute 02 toxicity, such as when total OTU leads to acute respiratory distress syndrome, with over 50% fatalities.

Yes, high 02 exposure is 'antibacterial' but most organisms that live within us are 02 users. Most bacteria that thrive without 02 cause disease in humans. The various bacteria in our guts balance each other, if anyone gets the upper hand, usually diarrhea results but is non-fatal [such as taking antibiotic pills which selectively kill a set of them.]

Dr. Thomas refers you to the textbook, Bennett and Elliott, which has a great graph of the subtle regional variations in circulation accross different tissues. Practically speaking within a dive, all tissues are equally oxygenated, but certain tissues are oxygenated first, and given priority in extreme conditions: such as the brain and spinal cord. This also one reason to avoid eating heavily during diving, as blood is also preferentially directed to the gut to speed digestion but not to the expense of other tissues if so warranted, such as the muscles in times of danger. This leads to indigestion and in severe cases vomiting!

 

[The Iceni]

Saturation once bubbled...
Among air divers, the long term effects of transient high pp02 show a definite reduction in vital capacity with time, i.e., a reduced lung elasticity.

If damage exceed repair, we have acute 02 toxicity, such as when total OTU leads to acute respiratory distress syndrome, with over 50% fatalities.

. . . This leads to indigestion and in severe cases vomiting!

Hi saturation,

What you post is absoluely true, however can I put this into perspective? It is generally accepted that high levels of ppO2 below 0.5 are entirely safe with prolonged exposures in healthy adults. Reversible changes in lung function tests can be detected in most subjects after about 24 hours exposure at 1 bar and the time to damage reduces exponentially with increasing ppO2. With extreme exposure irreversible lung damage occurs.

I would suggest that acute lung injury from pulmonary oxygen toxicity is quite rare.

In the past it was assumed 1 bar was the safe level for continuous use and a unit of exposure was derived given that there are 1440 minutes in a day; the Unit Pulmonary Toxic Dose.

This is now refined and is used by the Royal Navy, and NOAA to determine a safe exposure in any 24 hour period.

The formula used is UPTD = t mins x k, where k for each period of exposure is derived from the ppO2.

k = ((ppO2 - 0.5)/0.5) ^0.883(corrected see below!)

Thus at 0.5 bar k = 0 and at 2 bar k = 2.5

In any 24 hour period the reduction in lung function has been determined from empirical data;-

615 UPTDs in any 24 hour period gives a reduction in vital capacity of 2%

825 = 4%
1035 = 6%
1230 = 8%
1425 = 10%
1815 = 15%
2190 = 20%

As lung redundancy is considerable, a reduction of 10% in vital capacity is considered an acceptable exposure in recompression treatment, which again corresponds to continuous exposure at 1 bar (1440^0.883 ~ 1425)

CNS toxicity occurs at ppO2 in excess of 1.4 bar which has a k value of 1.63 giving a single 24 hour pulmonary exposure limit of 14.5 hours. Most rebreather divers use a set point of 1.3 bar, which gives a k value of 1.48 and a pulmonary limit for a single 24 hour period of 16 hours.

RN recompressioin treatment table 62 gives 637 UPTD. The maximum number of UPTD's recommeneded by IANTD for a day's diving is 850. They also recommend a planned limit of 300 units/day to allow for continuous, safe Nitrox diving.

Although technical divers will know that pulmonary effects are additive over multiple days of diving and the severity reduced by "air breaks", single day exposures of the magnitude to cause major problems are very unlikely in recreational scuba.:mean:

However, I agree that vomiting into one's mask is not to be recommended!

 

[Saturation]

Dr Paul Thomas once bubbled...
Hi saturation,
..
I would suggest that acute lung injury from pulmonary oxygen toxicity is quite rare.
...Although technical divers will know that these effects are additive over multiple days of diving and the severity reduced by "air breaks", single day exposures of this magnitude are very unlikely in recreational scuba.:mean:

Thanks Dr. Paul, an excellent summary of OTU, I find easier to pronounce than the original UPTD .. i.e., oh-too versus up t-thee.

What I suggests is the consideration of long term injury induced by chronic hyperbaric exposure. The OTU ergo whole body toxicities are 'acute' given the time frame, but there is speculation that repeated exposure-recovery cycles over years leads to irreversible changes.

The vital capacity recovers quickly, usually 1 day, and as long as 7 days, but other markers of repair, DLCO for example, take 1-2 weeks to recover.

Rebreather divers on constant pp02 have experienced transient persistent myopia for weeks, due to the hyperbaric effects on the lens. The same effect has not been seen in OC divers.

There is an unexplained long term reduction of VC in divers over years of diving. Its speculated it can be caused by simply breathing compressed gas, rather than the transient higher pp02 during the dive.

 

[Falcon99]

I just checked back in and to my suprize, the thread is wonderful!

One question though... Dr. Thomas, I did some surface plotting with the UPTD formula and was a bit confused at the outcome. It showed lower UPTD for higher ppO2 values. Changing the power to a -.883 seems to correct it. Please don't take this as a correction... It's more of a clarification question .

Here's what looks like the better plot...

James

 

[steevke]

Formula should be (IIRC)

OTU = t * ((ppO2 - 0.5)^0.83 / 0.5)

HTH

Steven

 

[Charlie99]

t * [ 0.5 / (ppO2 -0.5)] ^ -0.833...

or the equivalent t* [0.5/(ppO2 -0.5)] ^ (-5/6)

ref: http://www.drogon.net/ddplan/reference/cns.pdf
(an Erik Baker paper)

note that -5/6 is -0.833... , not -0.883

 

[The Iceni]

Falcon99 once bubbled...
. . . I did some surface plotting with the UPTD formula and was a bit confused at the outcome. It showed lower UPTD for higher ppO2 values. Changing the power to a -.883 seems to correct it. Please don't take this as a correction... It's more of a clarification question .

Oh dear,

That will teach me to copy from someone elses work without checking! :wacko: I simply used the formular provided in the booklet given me by the Royal Navy last week;- I belatedly undertoook their diving medicine couse.

They (I) have simply inverted the main part of the formula! Of course it should read

k = ((ppO2 - 0.5)/0.5)^ 0.833

NOT (0.5/(ppO2 - 0.5))^ 0.833 as I originally posted.

The constant 0.5 simply produces a graph with a k value of zero at 0.5 bar, and obviously k must increase if ppO2 increases. I must give Lieutenant Commander Mark Glover a call.

In practice I suggest we all should use the tables provided by our preferred agency if we want to track pulmonary oxtox. It is all to easy to get the sums wrong, particularly at a dive site.

 

[Falcon99]

Hi again.

Not breaking geek tradition, here's the plot with the correct formula. After looking at the formula a second time, I noticed it is essentially the same as taking the incorrect one and giving it a negative power. Your original reference, Dr. Thomas, was correct if given a negative power.

Note that (a^b)^c = a^(bc)

The inversion of the ppo2 fraction is a^-1.

Therefore (a^-1)^b = a^(-b).

In short, the first formula to a -0.883 power is correct.

Here's a color-magnitude plot for you, just for kicks

James

 

[Charlie99]

Falcon99 once bubbled...
In short, the first formula to a -0.883 power is correct.

The correct exponent is -5/6., i.e. -0.833... , not -0.883

Deco and oxygen tolerance are imprecise, but that doesn't mean that we have to add in more imprecision by using non-standard equations.

 

[The Iceni]

Charlie99 once bubbled...
The correct exponent is -5/6., i.e. -0.833... , not -0.883

Deco and oxygen tolerance are imprecise, but that doesn't mean that we have to add in more imprecision by using non-standard equations.

Does it make sense to measure the diameter of the earth with a micrometer?