100% Oxygen damages our brains ?!

aquaxel

i have addressed the scientist in charge, dr. harper, directly with our questions with a reference to this discussion and asked for bringing some light to the matter.

additionaly i posted the article to the commercial dive community at longstreath to see what comes out of there.

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aquaxel

QUOTES FROM LONGSTREATH URL:

1. try telling that to anyone who has witnessed the mirracle of HBO therapy.

2. That is news? The US Navy Diving Manual and the NOAA Diving Manual
have both been saying the same thing for a quite a few years. Look in
the Physiology chapter, under Oxygen Toxicity: short and long term
effects. But when you look at benefits versus long term effects, benefits
are gonna take it hands down. If you are worried about it, you can always
add your own CO2 - hyperventilate.

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rgds aquaxel

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Simon Mitchell

Thank you for explaining that to me. But seriously....

Breathing 100% oxygen at 1 ATA actually does increase tissue O2 content. A small increase in cerebral venous oxygen can be detected under these conditions. Breathing oxygen in the range typically used by rebreather divers, (1.2 - 1.4 ATA) will increase this a little further. I'm not sure how you define "significant" in this context. Perhaps you mean that somewhere on this continuum you enter the risk zone for cerebral oxygen toxicity.

I would agree with that; but this is where the disconnect between diving and the relevance of the research being debated here becomes important. These authors suggest that hormonal and autonomic responses to hyperoxia are potentially detrimental to the brain and other organs, and have shown that some of them can be ameliorated by breathing CO2. In diving, the risk of oxygen toxicity is markedly enhanced by increases in CO2, and our biggest problem is keeping CO2 normal. There are many factors that favor an increase in CO2 during diving, and we do not need to worry about the hyperventilatory response to hyperoxia that these authors are interested in.

In short, this study has little or no relevance to diving.

Warm regards,

Simon M

Abbo

Does anyone have any data on what is a typical PCO2 during a CCR dive with a working scrubber? I understand that it is somewhat higher than in air at STP, but what are the normal ranges?

apitkin

My impression of the paper is that the authors have allowed their discussion and more importantly their conclusions to go considerably further than is supported by their data and other published literature.

I do not know the level of peer review that an article published in PLoS Medicine undergoes; the nine months that elapsed between receipt of the article and its acceptance would hopefully entail some sort of academic scrutiny.

As Simon says, this paper is of no practical relevance to diving, although it is of some academic interest to those of us who regularly administer oxygen to children.

Andy

Joe Botz

I read some where that high concentrations of o2 produces free radicals, and what about those silent bubbles with their effect cumulative degeneration of blood vessels and secondary tissue lose.

aquaxel

dr. harper has kindly replied. here it is:

Dear Mr. Schoeller:

I appreciate your raising these issues with the study, and I thought that your comments were thoughtful. Our focus for the study centered on neonatal resuscitation and supplementary ventilation for children, particularly those who fail to breathe during sleep (congenital central hypoventilation syndrome), so I appreciate the heads-up on the diving concerns. I had been contacted by individuals who supply oxygenators for aircrews, who, of course, also find the topic of interest.
In response to some of the questions raised on the blogs, it is important to point out that the University publicity office may have stressed too much the findings that 100% oxygen is dangerous, not the MR data. We believe that finding to be true, but the relationships of hyperoxia and cardiac, peripheral organ, and brain injuries have been well-described before our study. The issues are well outlined in the Iscoe and Fisher paper referenced in the manuscript, and the concerns are being addressed in neonatal wards, especially in Europe where a Norwegian neonatologist has taken a strong advocacy position. Locally, Childrens Hospital at the University of Southern California resuscitates now with room air rather than hyperoxia (although my own institution will have none of it!!!).
I think it is fair to say that the cumulative evidence suggests that there is a significant problem with hyperoxia. Our contribution to the area rests with demonstrating what mechanisms can contribute to these problems (with MR studies), not to show one more time what others have already demonstrated. The problem with 100% oxygen, as one of the bloggers mentioned, is that such administration constricts the brain vasculature, interfering with the objective of supplying more oxygen to the brain. This phenomenon is well known, but is curiously overlooked by clinicians. In addition, cardiac output is impaired, and release of multiple hormones is altered- we mentioned glucagon, but there is a whole range of other agents. As soon as one mentions hormone release, then brain areas controlling the hypothalamus are suspect, and sure enough, those areas reacted strongly to hyperoxia. CO2 has a different action- it will dilate the vasculature, allowing better oxygen perfusion. Again, this has been known for a very long time. When we added 5% CO2 to the mixture, the excessive reactions in the insula, cerebellar cortex, hippocampus, etc., all hypothalamic regulatory sites, disappear. (I know medical students are taught that the cerebellum is only a motor regulatory area, not a hormonal/sympathetic area, but new studies show the fallacy of that knowledge).
All this is not to say that high levels of O2 don’t have a place- of course they do, for hyperbaric treatments for wounds, recovery from rapid return from the depths, etc. Our caution is that adding a little CO2 would help. Perhaps 5% is not necessary- we have not titrated the range of values, but it is the case that the evidence is in on how injurious 100% O2 can be to the brain and heart, and especially the young brain. As someone else pointed out in one of the blogs, we did not do a hyperbaric study, but I suspect the findings would be similar, or even enhanced. Nitrogen would not help; it has to be the addition of CO2.
I showed your offer of participating in another study to one of the co-authors; she was very enthusiastic. I’m not sure whether the logistics of the study make it possible, but we will look into it.
I would like to cc Steve Iscoe on this email. We would not have done the study without him, and he is much more knowledgeable on respiratory aspects than I am.
Thank you very much for raising these questions. We chose PLos Medicine because it is an open access journal (unlike most medical journals which are subscription-only, and thus viewed largely by institutional users). It looks like this time, the strategy to spread the information widely worked.

Best regards,

Ron Harper

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Simon Mitchell

Thank you. An interesting commentary. But just to be clear, it does nothing to establish the study's practical relevance to diving.

Simon M

aquaxel

mayb during transport on 02, resucitation or deco or chamber treatment...

+ they are interrested to do diving related tests.

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rgds aquaxel

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