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Perusing the recent posts, I noted the following quote from scubadoc in _persistent diving related sickness_:
Now, it gets interesting! Consider that this might be the result of multiple shallow dives effectively lowering your complement blood levels causing this picture. One of the causes of post-diving fatigue is thought to be due to the 'using up' of most if not all of your C3a, and C5a,d fractions in your blood by venous gas emboli of multiple shallow dives. This has even been shown to be protective to decompression illness on subsequent deep dives!
What an incredible set of findings. This theory strikes me as likely, primarily because, to paraphrase Murray Gellmann, the great theories that prove true always make previous mysteries disappear. This complement activation theory offers possible explanations for:
1. Unexpected (so-called "undeserved") hits (heightened sensitivity to complement activation)
2. Delayed hits
3. Post-dive fatigue
4. Reduction of post-dive fatigue on EANx
5. Reduced susceptibility to DCS of frequent divers
I have a few questions, though.
First, how else does the reduction of complement affect the human body? Does this reduced level reduce our ability to combat other illnesses or infections?
Second, asthma and chronic allergies can reduce complement. What else? Do recent infections, antibiotics, or HIV result in lowered complement levels?
Third, assuming the repeated dive acclimation works to eliminate C3, how long does it take the body to replace it?
There is a nice discussion of the Complement system in a section of the Merck Manual
The complement system is a highly complicated system of over 34 proteins in the serum of the blood that are set off into several different cascades of reaction upon encountering a foreign protein or antibody.
When this system is overwhelmed it leaves the individual immunosuppressed or more susceptible to invaders that would initiate that particular cascade. This includes infections, allergies and any other artificially introduced substance, such as bubbles. In other words, the bubbles are there and probably still do their damage from physically blocking the blood supply to tissues but do not institute the usual cascade of effects that cause long-term local damage, as with cytokines.
Asthma, chronic allergies or other chronic infections would deplete complement.
Replenishing complement would depend to a great extent on each individual, his nutritional and physical status and the cause of his complement activation.
One should be cautious with the "complement system" theory, since tese substances have not always been shown to be changed in diving situations where you would expect a change.
One knows that Dr. Deco’s bias lies with variable concentrations of tissue micronuclei to explain variations in the effects of diving. That is not to say that biochemical changes and edema do not occur, especially in cases where DCS has appeared and treatment has been delayed.
One of the interesting things about barophysiology is that there are many phenomena and a multiplicity of hypotheses. I have just returned from a NASA-sponsored meeting regarding barophysiology. A committee was called to study the data, and their conclusion was just the opposite of the committee that met previously on this same topic!
__________________________ Dr. Deco
So how close are we to really knowing the "facts" in these subjects or is the only thing that can be agreed is to disagree? I am curious as to why "their conclusion was just the opposite of the committee that met previously on this same topic"?
Is it a situation where there is more or new data to study or are these just different interpretations of the same data?
A committee tries to take all the real evidence about a subject (ie., data that's derived from RCTs) and come up with a concensus. Often, the data that is impressive to that particular committee points toward one conclusion that's entirely opposite of what a previous group might have surmised. This is not to say that one point of view is right or wrong - but that the data at that time seemed to indicate one thing uppermost in the minds of the committee.
This often happens in deciding the guidelines of treatment regimens for diseases - evidenced based treatment regimens.
It does make one think of the definition of a committee - a group of blindfolded people examining an elephant for the first time; one feeling only the trunk, another feeling only the leg and another feeling the tail, all coming to different conclusions as to what they were feeling.
The main thing to remember is that bubbles occur as a physical fact of inert gas coming out of solution due to increased pressure. The bubbles are known to cause the clinical picture we call decompression illness - how it does this is still being investigated.
This "agreement" is an interesting point, and it highlights the difference between science as taught in school and science as it is encountered in the front-line trenches . At the advanced level, science is not facts, but rather, it is an art. It is a feeling, an intuition; it is something based on experience.
Thus, at the “front,” scientists will interpret data in a way that depends on their experience. After many years, when all data is in, the picture becomes clearer. Then a consensus is reached, but it is seldom that way in those initial years.
I have often spoken to young people in school over the years about this same subject. Students see science as a collection of facts to be memorized. They find that boring. At the advanced level, this is not at all the case. Rather it is a case of evaluation, give and take, and re-evaluate. It is fascinating. BUT it can be perplexing for the nonexpert who believes that he sees facts changing daily before his eyes.