Pulmonary Oxygen toxicity

[canuckton]

I had an interesting question the other night....

We all know that Pulmonary toxicity starts to impair lung function after about 600 minutes, and severe breakdown at about 24 hrs (correct me if I'm wrong, I've never approached these numbers while breathing pure O2)

What about at lower ppO2's? For instance, if I used an O2 rebreather in a pool, at 10 feet, POT would be a danger after a marathon 600 minutes. But if it was set up to deliver 50% O2, would that double the time to 1200 minutes? Or is it a more complex relationship? (assuming, of course that my scrubber pack would be as big as a truck and last that long...)

Not only that, but is there a ppO2 over .21 ata that can be used for prolonged periods of time (say, 100 hours) without encountering POT problems, ever? If so, how high is it, and how did we arrive at that number?

Just for the record, I phoned DAN on this one, and they were not able to answer, though they said they'd phone if they did get an answer.

Whaddya think??

 

[madmole]

What you need are the NOAA tables that define limits for long term exposure to O2 rich mixes.

NOAA Oxygen Exposure Chart (this is for CNS and OTU)

PO2 Exposure Max Single Exposure Max 24 Hour Exposure
(Atmospheres) (Minutes) (Minutes)
1.6 45 150
1.5 120 180
1.4 150 180
1.3 180 210
1.2 210 240
1.1 240 270
1.0 300 300
.9 360 360
.8 450 450
.7 570 570
.6 720 720

but this table is also CNS based

There is also a table for multiday diving. The limits for each days exposure go down the longer you dive for. pulmonary tox only really becomes a problem when you do multiday diving. For example on my Inspiration. If I dive for 3 hours a day for 7 days then I hit the pulmonary tox limits on day 7 (and thats on 1.3 bar PPO2). But like all effects it is not clearcut and your mileage may vary. there are some individuals who are very sensitive, and as I'm a paramedic I have seen people react to O2 after 20 mins or so at 40% in the back of my ambulance (Elderly and its because we have washed out the CO2 in their systems)

The BSAC also publish a limit of 800 OTU units a day for their members and publish tables to calculate CNS and OTU (Pulmonary) Tox

The normal figure of 0.5 bar PPO2 is quoted as the highest level that can be breathed continously without symptoms. All levels above this are toxic

 

[madmole]

O well the table was formatted nicely when I sent it

 

[Dr Deco]

Dear Readers:

To my knowledge, the pulmonary toxicity limits end at about less than ½ atmosphere of oxygen. At this point, it is believe that this oxygen concentration is within the natural ability of the enzymes of lung tissue to combat the reactive oxygen intermediates.

When one goes to higher partial pressures, injury will eventually occur to the lungs with the formation of connective tissue (fibrosis). Unfortunately, this can progress to a point where it is irreversible and the individual needs more and more oxygen, gets more and more fibrotic, and eventually dies.

Dr Deco :doctor:

 

[DivingDoc]

I've attached a file of some abstracts related to this question. Unfortunately, some of them are a bit too much into basic physiology -- the part I've forgotten -- for me. Also, I am unfamiliar with the term, "saturation diving." Perhaps someone can help me here. The Norwegian study also uses units with which I am unfamiliar.

So -- Dr. Deco -- would it be possible to get pulmonary Oxtox from intermittent hyperbaric O2 exposure over a 7 day period with, say 13-14 dives all using 32-36% Nitrox (32 for deeper dives of 80-100 fsw and 36 for shallower dives of 50-60 fsw)?

I'm attaching a file with the abstracts.

ET

 

[BRW]

According to many data/fits and likelihood
analyses, neither pulmonary (measured in OTUs
or UPTDs) nor CNS (measured in fraction of
total allowed exposure time) IS MUCH of a problem
below ppO2 < 0.50 atm.

Lambertsen (building rebreathers such as the
LARS series used by UDT, SEAL, and SF folks)
at the the Unversity of Pennsylvania clocked
most of this work, and it's still valid today.

So, bottom line, if your oxygen exposures
stay below 0.50 atm you really have little to worry about -- full body (pulmonary) or
neurological (CNS) toxicity.

The reams and reams of tech diving profiles
reflect this fact, especially on the extreme
side -- real deep for real long on depleted
oxygen bottom mixes, but pure oxygen mix switches
in the shallow zone. Bookkeeping of oxygen dose
is the trick here.

Bruce Wienke

 

[Dr Deco]

Dear DiveDoc:

Saturation Diving

Saturation diving refers to exposures of an individual to pressure such that all of the inert gas has been taken into the body for that depth (pressure) and the tissues are not saturated. Some will saturate faster than other (blood is the fastest, brain and cord are next). The process is complete after a couple of days. Saturation according to a dive table is after six halftimes of the longest compartment. This means that, after this duration, the table maker does not believe that the incidence of the biomarker for DCS will change

Oxygen Toxicity

I personally , have little experience with oxygen toxicity (in nitrox) and diving. The references that you supplied indicate that there may be some subtle changes (CO diffusion) other than change in vital capacity (the old standard). I have experience with hyperbaric oxygen therapy and know that little is seen (in these resting individuals).

As Dr Wienke indicated in the posting above, recreational divers seldom (if ever) experience problems associated with pulmonary toxicity. This is not necessarily the case with technical diving. Acute exposures to oxygen are certainly possible for CNS effects, and this is controlled by the proper nitrox mix.

Possibly other readers will have some comments on this topic.

Dr Deco :doctor:

 

[chuckrt]

I work in a surgical intensive care unit as a Lic. RRT and deal with this problem daily in compromised pts.. At 1 atm we do not get concerned about > 60% ox till around 2-3 days. This will then manifest as Leaky Capillary Syndrom and start causing increase in ventilation pressures. I have not seen a case unless the pt. was intubated. There have been many cases of long term hi oxy. via mask with no toxic symptoms at our hospital. I have not seen cns toxicity at any time maybe the drugs pts. are on hide the symptoms, I don't no. Bottom line is if doing recreational diving and following the prescribed tables there should be no problems. In the last 20 years I have seen many improvments in treatment for ox tox and have seen a dramatic increase in survival rates.

Bottom line: there shouldn't be concern if you are doing things right but if you are not following the rules don't do it.

chuckrt

 

[canuckton]

chuckrt,

Interesting, interesting....

we weren't really worrying about oxtox (either type) within our conservative and well-validated diving tables...

rather, I was concerned about long (looooooooong) exposures at very shallow depths, which are pretty common for harvest divers up here. I am not a harvester myself, but there were some questions about gas management, and the issue came up.

It seems that there was a project to measure lung degradation after long periods of breathing 36% at 1.5 ata, and after a 52 hour exposure, no breakdown of lung function was detected.

Not only that, but apparently, one can dive shallower than 20 feet pretty much indefinitely without having to worry about decompression, although age and mass affect the amount of Doppler bubbles after such a dive.

 

[Dr Deco]

Dear Chuck:

I was taught that oxygen toxicity limits are for healthy individuals. Those who are compromised and not receiving oxygen as they should into their capillaries are manifesting some limitation. This limit might also be expected to reduce the progress of oxygen toxicity.

In any case, these patients can be exposed to higher partial pressures of oxygen and the negative responses are muted and delayed. (So I was taught, anyway.)

Dr Deco :doctor: