Chronic oxtox

[jasondrake]

I've been diving nitrox for a while and read piles of bumf on oxygen toxicity, acute and chronic. Pulmonary exposure seems to be a limiting factor in deco scheduling on extreme technical dives, with various methods of calculating maximum allowable exposure over a dive, series of dives and weeks of dives. I understand that oxygen is potentially damaging to lung tissues and why. However, I had a long conversation with a doctor fried who works in the ITU in Glasgow (asked to remain nameless) who tells me that they regularly have ill patients on pure O2 (realistically 90% due to masks etc) for many days 24hrs a day. No air breaks etc. I asked if this was damaging their lungs and he said sure, a bit, but nothing to worry about and certainly nothing permanent. He laughed, as did a colleague, when I explained the diving line on chronic oxtox. Long term exposures to high F02's seem the norm in hospitals.

Any thoughts?

[Mark Scott-Simons]

In hospital they have different methods of delivering oxygen mask, nasal tube, tent etc each give different FO2 eg a nasel tube gives, IIRC, FO2 of 40% ish.

As to exposure times diving increases your susceptability to CNS toxicity for reasons not completely understood but one of which, very relevant here, is exercise level. A seriously ill patient obviously is not doing any where near the exercise level of even a relaxed diver decoing on a blob.

Divers have had tox events at 1.2 Bar (Comex diver working) yet bent divers are regularly treated at 2.8 bar with an almost zero incidence rate in pots. Though some do report "fried" lungs as an after effect from the pulmonary effect.

As for pulmonary exposure, ppO2 of 0.9 bar for 24 hours gives a UPTD count of 1100 which is well within limits even if continued for a few days [OTU of 4000 produces in 50% of people a reduction in vital capacity of 50%, plus pain. IIRC]. Again the relaxed state of the patient would increase their tolerance. The patient once taken off a mask would probably be suffering some effects from the exposure including pain and decreased breathing efficiency but as they are stuck in bed and probably on pain medication these side effects are very acceptable especially given the alternatives - seriously ill or dead.

Its possible your friends didnot realise the effect that being at pressure and underwater has on the sport and commercial diving fraternities. Toxing is often fatal underwater and is not uncommon whereas its very possible your friends wont have seen an OxTox event. Plus finishing a dive with lungs fried from pulmonary effects hurts. And for people doing this for fun or work is unacceptable.

So bottom line we have different degrees of acceptable exposure cos we are after different experiences.

Scotty

Edit: missing 0 in "OTU of 4000 produces in 50% of people a reduction in vital capacity of 5%, plus pain. IIRC" 5% -> 50%

[Andy Phillips]

As it goes the effects of O2 both CNS and pulmonary are fairly well documented, in a hospital the risks of pulmonary are offset against the benifits. The one far outweighs the other.

There have been a significant number of tests done for CNS in chambers which is where the max value of 1.6 PO2 comes from. The biggest threat comes from people who have been working fairly hard at depth as the surface they think that they will be OK to raise the PO2 to 1.6 for deco, wrong, they have a high level of CO2 in there system, the body thinks I need more O2 and so increases the percentage of 02 in the system. Bang, a hit. This for me is why I set a max O2 of 1.5 on deco, and why I will never use 100% o2 on deco, I have a family I would like to see grow up.

Lastly, pulmonary, for the most part will take care of itself provided you watch your PPO2 level, and overall O2 clock during a repetative dive series. All that will happen is you will grow older quicker.

Andrew

[Dr Stevil]

<font color='#0000FF'>Thoughts? yes, I've got a couple.

The first one - and I'm not having a go at you Jason, it happens a lot - is that a weekend nitrox course or two seems to mislead many people to believe they are then equipped with a broad understanding of the myriad effects of oxygen biochemistry; a subject you could study from now &quot;until the 12th of never&quot; and still not get to the end of it (I've been doing it for the past six years and will continue to do so far at least another 2 &amp; 1/2 years in my current job).

My PhD topic was about oxidative-damage in biological systems, &nbsp;particularly in terms of proteins (which make up the largest percentage of the dry weight of your body), so as you can imagine I've read quite a lot on the biochemical effects of oxygen, 99.99% of which you won't find in any diving related texts (I've posted a couple of oxy-facts below).

If anyone should be bored enough to be interested, I could probably do a synopsis from my thesis introduction on &quot;the superoxide theory of oxygen toxicity&quot;. In the meantime, for anyone with a smattering of scientific knowledge (or a lot of perseverance) I can recommend leafing through &quot;Free Radicals in Biology and Medicine&quot; by Halliwell and Gutteridge.

Chee-az
Steve
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Some Oxygen facts:

it is oxygen (in the form of oxygen free radicals or reactive oxygen speces: ROS) which has been implicated as a (or the)causitive agent in: aging, many forms of cancer, Alzheimers disease, Motor Neurone disease, muscular dystrophy, huntingdons corea, AIDS, &nbsp;etc etc.....

The only reason we can exist in this 21% O2 atmosphere is that we possess numerous oxygen detoxifying systems,

Once upon a (pre-historic) time, the release of oxygen into the atmosphere wiped out over 90% of all life on earth

[MATTBIN]

Just goes to show how much we know about diving and the gas we use doesnt it?

AndyP - If I remember correctly doesnt GI3 advocate only 100% O2 deco, certainly seem to think he ruled out 80%, makes you a stroke my friend!

Matt

[jasondrake]

I understand why my thread had no relevance to acute cns toxicity, but it's the pulmonary bit that baffles me. &nbsp;I've done a bit more than the standard weekend course, and have a biology degree although obviously not as specialised as what Steve W has done. It's because I've studied (and even carried out god help me) some 'science' that I have absolutely no faith in scientific statistics, published or not.

I appreciate that the environments of a diver and a patient are wildly different and very significant. Thats kind of why I posted.I was just interested that a guy who's done 10 years of medical exams and spent 10 years administering oxygen to people, while closely observing their cardio-respiratory health, feels that fear of oxygen lung damage while diving is a joke. This guy has a profound understanding of cardiorespiratory physiology, gas physiology and &nbsp;so many other ologies that I coudn't keep up. I personally prefer to follow the advice of those who 'do' over what the books say. But this time I've no idea. Mind you I've smoked so much crap over the years that my lungs are probably beyond salvage anyway.

[Tim Ingmire]

can I ask a question here?

AIUI CNS tox is the main cause of concern for those diving and is therefore important to manage your 'dose' over time / course of dives - Pulmonary Tox is covered in the manuals but really only for 'completeness' of info as it is not a major cause of concern for divers as it requires very long exposure times that we just don't suffer.

Or am I just plain wrong?

[Bob Cooper]

A very interesting thread this......With some excellent, and very well informed posts. &nbsp;I'm certainly no expert on cardiorespiratory physiology but I have done some diving...... The primary &quot;risk&quot; associated with high PPO2 oxygen exposure is that of oxtox. &nbsp;The effect of CNS oxygen toxicity in diving is.....drowning. &nbsp;An O2 hit can result in a convultion which will *drown* you. &nbsp;That is the difference between hyperbaic medicine, where patients are regulrly exposed to PPO2'sof 2.8 bar or whatever, and diving, where we like to set a max ppO2 of 1.6 bar at deco and a much lower limit for the &quot;working&quot; portion of the dive. &nbsp;You can tox in a chamber quite &quot;safely&quot;. Tox in the water and you need a really switched on buddy team to help you out.

[Andy Phillips]

This really is Steve W's field, but, my understanding, and this comes from floating about on the periphery of the field is that over the last few years it has been discovered that by subjecting the body to high PPO2's i.e. breathing O2 at pressure has led to some fairly miraculous results in certain diseases, and in the treatment of burns, there is some research currently in Cancer Research with surprising results.

O2 itself is fundimentally toxic, it is what causes us to age, but Steve W can add more to this line.

What Bob say's is correct, for diving we are concerned with CNS toxisity, this can cause a seizure and thus drowning. This being said, damage can be caused to the lung tissues due to low presures of O2 but as long as we are aware of this and pay it respect we can ignore it for diving.

Andrew

[jasondrake]

On a slightly different note, does steve w or anyone else know if any studies have been done on the in interaction of acute cns oxtox and nitrogen narcosis. Nitrogen at high pp obviously has &nbsp;a 'soporific' effect on the nervous system, and high oxygen pp seems to have kind of the opposite. (twitchy lips and spasms etc) I'm sure the areas of biochemical effect are probably different and complex but could one counteract the other? For intance at 70metres on air could the high levels of nitrogen delay the onset of acute cns? I'm not suggecting anyone tries this but has anyone ever had an O2 hit while diving deep on air?