28% Nitrox

[BoltSnap]

Answers to some of the questions and comments posed above are found in the article I referenced earlier.

Figure 2 shows a graph from a Lambertson study. There was no CNS toxicity below ppO2 of 2.0. However, the study was performed in a chamber, and there is evidence that wet immersion presents greater risk than seen in a hyperbaric oxygen chamber. The take-home point from the figure, though, is to look at the CNS Toxicity curve, and note the sharp, exponential rise at the elbow of the curve once the toxicity threshold is reached.

The big question is, where is that elbow when diving?

The answer to that is: Who knows? Look at Figure 4 where Bitterman references a study by Donald. Donald took the same diver and had him do the same hyperbaric oxygen profile 20 times over 3 months. Each time he "dove" until neurological symptoms occurred, and each time the symptoms occurred after a different length of exposure ranging between 5 minutes and 2.5 hours! Heck, that might as well be random!

Bitterman concludes: "As can be seen, there are large day to day variations in time duration of symptoms, suggesting that there is no fixed, personal, predetermined threshold of tolerance to oxygen toxicity."

String: One of the risk factors mentioned is age. When Bitterman talks about possible mechanisms for how CNS toxicity develops, he discusses vascular modulation and enhanced antioxidant states. These are things that can be affected by age very much, so it seems reasonable that age might be a factor. (As a diver who is a little above the average age, it certainly makes me want to be a little less cavalier than I have been.)

Can you please give the reference to this article again? I don't seem to be able to find the previous reference.

 

[wve]

See Post #83. There is a link. I'm not where I can re-post the link at the moment.

 

[DevonDiver]

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[RJP]

What purpose have you chosen 28%? If you are not diving deeper than 110 feet you could just use 32% because it is easier to get fills.

You just answered your own question.

 

[adutto]

Agree with everyone... there are only 2 "standard" EAN tables (32 and 36), my suggestion would be to do the calcs manually and then use a programmable computer in which you can put the 28% mix.

Just a thought, around here it would be difficult to find someone that do this mix for you, but I believe that in the US that shouldn't be a problem right?

Regards

 

[String]

Bitterman concludes: "As can be seen, there are large day to day variations in time duration of symptoms, suggesting that there is no fixed, personal, predetermined threshold of tolerance to oxygen toxicity."

Other studies have found that BUT there are papers going back 60+ years that have identified in some individuals having a higher tolerance than others. Its mainly random but there is a background trend for a small group of people being more tolerant to higher pO2s than others.

String: One of the risk factors mentioned is age. When Bitterman talks about possible mechanisms for how CNS toxicity develops, he discusses vascular modulation and enhanced antioxidant states. These are things that can be affected by age very much, so it seems reasonable that age might be a factor. (As a diver who is a little above the average age, it certainly makes me want to be a little less cavalier than I have been.)

I can see how circulation as a whole can affect the risk of DCS but this isnt directly related to age. Granted with age the incidences of reduced circulation and so on are higher than when younger its not guaranteed.
Im not aware of any studies with data statistically linking age to an increase of DCS.

 

[wve]

Other studies have found that BUT there are papers going back 60+ years that have identified in some individuals having a higher tolerance than others. Its mainly random but there is a background trend for a small group of people being more tolerant to higher pO2s than others.

Yeah. I was quoting Bitterman's conclusion. The interesting thing about this particular study was the wide variation in a single individual who provided his own control.

I can see how circulation as a whole can affect the risk of DCS but this isnt directly related to age. Granted with age the incidences of reduced circulation and so on are higher than when younger its not guaranteed.
Im not aware of any studies with data statistically linking age to an increase of DCS.

As a general rule, older folks have worse circulation than younger people, primarily due to atherosclerosis, although other factors can also come into play. I can't quote you any studies relating age to DCS risk either, but there must be some because most reviews cite it as a risk. Of course, there are exceptions to every rule.