O2 Narcosis

[Lost Yooper]

Ok docs, I'm interested in the artcle that says that CO2 is 120 times (perhaps several hundred times) more narcotic than N2 http://kupla.tky.hut.fi/~arn/ss_2001/material/Oxygen Narcosis.htm

Will someone diving air to 200' produce more CO2 than if he were to use an 18/35 trimix (for example)?

If the person were to exert at depth, using the above scenario, would the air diver produce more CO2 quicker than if using trimix? Once the CO2 is "getting out of hand", it will continue to accumulate and the narcosis will get worse, right?

So what I'm getting at is whether or not deep air diving is more dangerous for the physiological reason of producing very narcotic CO2? Does trimix reduce the amount (or time) of CO2 made, especially during exertion at depth?

Thanks,

Mike

 

[The Iceni]

Come on Yooper, you know this already. I am sure!

The only natural source of carbon dioxide is from cell metabolism. The amount produced by the body is only determined by exercise and so is not DIRECTLY related to depth. This is why the scrubbers in rebreathers last the same regardless of the depth dived (and indeed why the oxygen in the rebeather lasts just as long regardless of the depth dived).

In my opinion the toxic problems of carbon dioxide far outweigh any risks of narcosis.

On the other hand at depth the work required to move gas in and out of the lungs does increase, which means in practice that respiratory dead space increases for any given effort.

So at extreme depth - with open circuit at least - there is a real risk of the build up of CO2 to toxic levels.

As Helium is much less viscid than Nitrogen, simply because Trimix is easier to breath than air, the risks of such hypoventilation and CO2 toxicity are lessened.

This is just one of the reasons Helium is used as the diluent for deep dives.:mean:

 

[Lost Yooper]

Well, I might have suspected this, but I wanted to be 100% clear.

Is there any evidence that high PPCO2 causes any physical, long term damage (measured in years) of any sort?

Thanks Paul,

Mike

 

[Dr Deco]

Dear Mike:

The question of carbon dioxide intoxication is one that your body will answer for you. In concentrations more than a few percent, it is very uncomfortable. You experience “air hunger” or the feeling of suffocation, and then intense headaches. These effects appear to be the most serious problems.

The only time that one would really worry about carbon dioxide (of which I am aware) is in chronic expose to low-level increases. These might be in factories, mines, in submarines, or (as concerns NASA) in spacecraft cabins.

It has been postulated that long=term exposure could lead to a slight acidosis (= blood becomes somewhat more acidic) and this in turn could lead to a loss of minerals from the bones. These situations are argued since good long-term data does not exist, (as far as I am aware).

Curiously, it has been reported over that past decade that excessive drinking of carbonated beverages has been linked to bone mineral loss and resulting osteoporosis in older individuals. This is only will excessive imbibing, not a couple of cans of pop a day. Whether this is due to something connected with carbon dioxide has not been proven, but it is linked to carbonated beverages independently of which kind.

Thus, when talking about adverse effects of CO2, diving is not the way to go if you wish to get them. Suffice it to say, that a diver will know the unpleasant effects of carbon dioxide, long before there is a chance for a permanent physiologically deleterious effect.

Dr Deco

 

[The Iceni]

Hi Mike,

Your thirst for knowledge appears insatiable!

I cannot imagine a set of circumstances where the effects of prolonged hypercapnia (raised pp CO2) could be isolated from other variables and accurately measured in the body's tissues in a high pressure environment but I do know that the body can normally buffer the acidic effects as I discussed above.

What I do know is that traditionally there are two kinds of clinical presentation in patients with chronic obstructive pulmonary disease (COPD), the "blue bloaters" and the "pink puffers" whose main problem is chronic hypercapnia.

In the the first group, the cyanosis due to the poor oxygenation is the main feature while in the second group the dilatation of the superficial vessels of the face due to chronic CO2 retention appears to be dominant.

All suffer from the effects of both hypercapnia (predominantly) and hypoxia. Many develop pulmonary hypertension, right sided myocardial strain and cor-pulmonale - eventually (often after many years) succumbing to heart failure. (I would be interested to see if they are more prone to osteoporosis, which is usually attributed to the oral steroids which are prescribed for many sufferers of COPD).

I am not at all sure that this is in any way relevent to changes experienced by fit individuals when diving.