Question: Are you aware of any documented cases of a diver with DCS symptoms and undetectable bubbles using Doppler instruments? (Sincere question, not intended to be confrontational or snarky)
To reinforce your statement, there are also many identified and unidentified human variables. The only reliable and absolute DCS prevention is stay at sea level (people can also be bent in unpressurized aircraft).
Maybe some of this will help the OP and some other readers:
It is difficult to believe that bubbles never play any role in DCS, at least in severe DCS cases. Doppler studies actually show blocked vessels and autopsies show dead tissue. Like everything in medicine though, I also dont believe that the simple physics of bubble formation is the only bad actor. DCS may not always be the result of blocked blood flow due to bubbles, but it
is caused by gas being released from tissues more rapidly than the body can accommodate. That in turn
may cause physiological responses that produce symptoms long before compromised circulation has an impact.
Hello Akimbo,
Food for Thought: 21 years ago, in his masters thesis, Sawatzky systematically analyzed maximum Doppler scores and DCS incidence in a total of 3,234 dives. He found only one incidence of DCS not accompanied by detectable bubbles, giving a negative predictive value of 0.99 and a sensitivity of detectable bubbles as a test for DCS of 0.99. However, Sawatzky also detected bubbles without any symptoms of DCS, which gave a PPV of only 0.04! This illustrates that having detectable bubbles yields only a 4% chance of developing DCS! Even when using high bubble grades as test criterion, the PPV is low. (PPV - positive predictive value).
Please let me reiterate that I NEVER stated nor do I believe that bubbles do not play a role! HOWEVER, given the above and other studies, it is hard to argue that bubbles ALONE cause DCS. Current scientific endeavor in DCS research focus on exactly on that - what is the or are the cofactor or cofactors.
So please don't restate or suggest that I said or intended to imply that bubbles never play a role - I don't. But it is also incorrect to state that bubbles will cause DCS! If that were the case, most of us would get bend.
In the past with the understanding at THAT time, the only means to reduce the risk of DCS (since we cannot prevent it or else you don't dive or go to space), was to follow tables, de-nitrogenate, attempt to compress micro-nuclei, etc. i.e. control the bubble.
As more data and studies became available, the focus to control the bubble has changed. Although still important, we now know that most of us bubble regardless of following decompression procedures and only very few get bend. So the new question is: Why do some bend and not others?
The typical "undeserved hit' is an example of that question. Why did this person bend when he/she did everything right? And, that is precisely what some scientist currently focus on.
Articles on this and other topics are posted on the Add Helium website:
Add Helium - The Rebreather Epicenter for divers to read themselves if curious.
Thank you for your question. It allowed me to clean up/clear up any misunderstandings.