This is an amusing thread
It sure is. It has meandered quite a bit more than what is normal for a Scubaboard thread and should probably have been split at one point since the last pages aren't (IMO) particularly Basic any more, but that's another discussion.
For those of you trying to figure out what Tarponchick meant by her post, let me just say that she has views about diving with nitrox that are very much out of mainstream thinking.
Not just about nitrox diving, but also about science in general and the pathophysiology of DCS in particular. I have no hope of convincing
tarponchik that s/he is wrong, but for the benefit of other readers, I'll quote a few of his/her statements and show how far off s/he is, and also his/her disingeniousness in his/her argument.
this BS about "tissue stress" w/o any reference whatsoever? As far as I know, tissue stress is nothing but a theory.
"Nothing but a theory" is a well-known gambit played by people who have absolutely no knowledge about science. In science, a theory is about as good as you can get it. A theory is consistent with all observed data and can successfully and reliably be used as a prediction tool. Like Newton's theory of gravity, Darwin's theory of evolution or Einstein's theory of relativity.
I gave my opinion, that is it.
"Everyone has a right to their opinion". Sure, but no-one has the right to their own facts. Or, as philosophy professor Patrick Stokes
so eloquently put it:
The problem with “I’m entitled to my opinion” is that, all too often, it’s used to shelter beliefs that should have been abandoned. It becomes shorthand for “I can say or think whatever I like” – and by extension, continuing to argue is somehow disrespectful. And this attitude feeds, I suggest, into the false equivalence between experts and non-experts that is an increasingly pernicious feature of our public discourse.
[...]
Plato distinguished between opinion or common belief (doxa) and certain knowledge, and that’s still a workable distinction today: unlike “1+1=2” or “there are no square circles,” an opinion has a degree of subjectivity and uncertainty to it. But “opinion” ranges from tastes or preferences, through views about questions that concern most people such as prudence or politics, to views grounded in technical expertise, such as legal or scientific opinions.
You can’t really argue about the first kind of opinion. I’d be silly to insist that you’re wrong to think strawberry ice cream is better than chocolate. The problem is that sometimes we implicitly seem to take opinions of the second and even the third sort to be unarguable in the way questions of taste are. Perhaps that’s one reason (no doubt there are others) why enthusiastic amateurs think they’re entitled to disagree with climate scientists and immunologists and have their views “respected.”
Someone seems to have gotten their degree at Google University.
Or, to put it in a somewhat less snarky way: When someone says they "googled it", it's a strong indication that they know squat about what they're talking about, but they went on Google and read either the first hit, or the one that aligned best with their preconceived opinions. I'm not saying that this necessarily is the case here, but it should be considered as a possibility.
you have to either dive on NITROX or cut bottom time. At least, this is my understanding of the article I found.
This silly fallacy has already been thoroughly debunked by
@boulderjohn in
post # 118.
I'd recommend you read up the science and learn what stress is. To give you a hint, stress is our body's response to some unfavorable external conditions. Therefore, bubbles are not a sign of stress. They may cause stress, however, this has not been demonstrated. So until you prove that our body is stressed by the bubbles, and this stress can be measured (i e, in levels of released hormones, catecholamines etc) I object to the use of the term "stress" in relation of N2 bubbles formation.
Another interesting gambit: Find one definition of a term, but make sure it's not related to the common use of the term as it has been used in the discussion. Then use that definition to argue that the other part is wrong. "Stress" is a very unspecific term which - in medicine and biology - may indicate a response to some unfavorable conditions. I'll concede that point, but the following arguments fall flat to earth. Both "tissue stress" and "surgical stress" have their own Wikipedia pages where the terms are defined pretty well, and having talked in person with quite respectable hyperbaric medicine scientists, I understand why "stress" is used as a shorthand term for the physiological reactions to nitrogen bubbles in our tissues. In short, bubbles not only cause mechanical damage by appearing in joint or nervous tissues, but they also provoke a number of physiological reactions, including a immune system response to the hydrophobic nature of the bubbles. This is one of the reasons that it's important to start hyperbaric treatment of DCS patients as quickly as possible, because we want to minimize the body's physiologic response to bubbles.
If I wanted to be a bit sarcastic, I could point out that in physics, "stress" is simply force per unit area and does not lead to the release of "hormones, catecholamines etc", but that would be rather off topic here, so let's go back to what the science says about the body's reaction to nitrogen bubbles. Let's use
the review article I've already linked to, because I think it's a pretty good article.
VGE does not necessarily lead to DCS, but VGE is an indicator of decompression stress.
Arterial bubbles are often connected to the more serious cases of decompression injuries (Neuman 2003), which indicates that VGE is a relevant stress indicator for such symptoms
Note that the authors here use the term "decompression stress" in a reputable peer-reviewed scientific journal. This is a pretty strong indication that the scientific community recognizes that term and that it has a specific meaning.
Several studies have shown reduced endothelial function after exposure to vascular bubbles
[...]
Even in the absence of clinical manifestations, VGE can cause changes in barrier permeability. Proteins and leukocytes can be allowed into the extravascular brain tissue with subsequent formation of edema if the blood–brain- and/or blood–lung barrier (BBB and/or BLB) is broken down (Hjelde et al. 2002; Chryssanthou et al. 1977; van Hulst et al. 2003). Polymorphonuclear leukocytes (PMNs) play a central role in the bubble-induced inflammatory response (Martin and Thom 2002; Nyquist et al. 2004). Nossum et al. (2003) demonstrated reduced PMN infiltration in rabbits given anti-C5a monoclonal antibody and thus protected the endothelium against injury caused by small amounts of bubbles. From animal models of gas embolism, leukocytes have been implicated in the progressive fall in cerebral blood flow and decreased cerebral function (Dutka et al. 1989; Helps and Gorman 1991). PMN accumulation in rat brain is also demonstrated to be a part of an acute inflammatory response to brain injury (Clark et al. 1996; Schoettle et al. 1990). Schoettle et al. (1990) found a significant correlation between PMN accumulation and the development of cerebral edema. Similarly, leukopenic dogs suffered less microcirculatory damage after injection of air into the internal carotid artery than did control dogs (Dutka et al. 1989). In a recent study by Thom et al. (2011), circulating microparticles (MPs) were found to be elevated by decompression stress. Decompression from greater pressures resulted in higher amounts of MPs from different cell types, and the study gave a pathophysiological link between MPs and tissue injuries. Further, in a study by (Glavas et al. 2008) a possible link between formation of VGE after a single dive and impaired arterial vasodilatation were found. Together with the previously mentioned work, this points toward the hypothesis that DCS is an inflammatory disease.
(my emphasis)
I guess this directly contradicts
tarponchik's claim that bubble formation doesn't affect the tissues negatively (AKA "stresses" the tissue). And just, to provide the tl;dr verson of the last arguments:
There is evidence that the occurrence of at least some forms of DCS is not entirely consistent with purely physical processes.
I leave it to the informed reader to determine whom they want to listen to: Highly experienced and competent divers and diving instructors who have participated in this thread (plus literature written by competent hyperbaric scientists), or
tarponchik, who repeatedly has used numerous gambits and fallacies in their arguments and generally argues concepts that definitely aren't consistent with what diving certification agencies teach today.
Personally I know which viewpoint and research I am going to follow.
