"Undeserved" DCS hits

[Cave Diver]

Thanks Steve. I'll try to dig through some of Rubicon's stuff too. It would be very interesting if it pointed to a better immune system making some people less predisposed to developing DCS.

 

[boulderjohn]

There are studies, and I'll have to ask Gene to either look 'em up or I will have to do the leg work myself, into how the body's immune system reacts to bubbles knocking around in the bloodstream... bubbles are little foreign bodies which activate the complement complex, et al.

Heard a presentation one time from a nurse practitioner who did the research for her master's degree.

I think I know the study. I was interested in the topic and started threads in the Ask Dr. Decompression forum.

http://www.scubaboard.com/forums/ask-dr-decompression/279200-dcs-immune-system.html

http://www.scubaboard.com/forums/ask-dr-decompression/297493-dcs-immune-system-redux.html

As a part of that research, I corresponded directly with Gene Hobbes on the topic, and he and I looked for further research.

The problem is that her research showing positive results has not been replicated anywhere. It is not currently a widely held belief. It has not been disproven, but her initial work has not been supported by later work.

There are still people who looked at the original work and are repeating it. One agency, in fact, says it represents current thinking on the subject. As far as I can see, though, it does not.

 

[MXGratefulDiver]

Even "unexplained" is a load of crap yes?

Like JC said, it's always the guy who is overweight and totally out of shape that is like, "I didn't do anything wrong, I don't know how this could have happened"

I'm sure that if you truly delve into the causes of every DCS hit, you'd find at least a POSSIBLE and maybe even probable explanation.

Ah, not so ... my friend John Rawlings got terribly bent during a photo shoot for ADM in the Bahamas, and he's rather thin ... and in pretty decent shape for an old dude. According to his profiles, he was totally within NDL's on all of his dives, and being a very experienced diver who's been doing tech dives for years I'm pretty certain he handled his ascent profiles properly.

I think it boils down to the fact that there are a lot of variables involved, you're dealing with a body that wasn't designed for what we do to it every time we go underwater, and there's always the potential for all those variables to align in a way that's not going to produce a happy outcome. It's a risk we all take every time we go diving.

As Ross Hemingway once put it ... "we're all lab rats" ... anybody who thinks it can't happen to them because they've considered all the variables is kidding themselves.

... Bob (Grateful Diver)

 

[HowardE]

Ah, not so ... my friend John Rawlings got terribly bent during a photo shoot for ADM in the Bahamas, and he's rather thin ... and in pretty decent shape for an old dude. According to his profiles, he was totally within NDL's on all of his dives, and being a very experienced diver who's been doing tech dives for years I'm pretty certain he handled his ascent profiles properly.

I think it boils down to the fact that there are a lot of variables involved, you're dealing with a body that wasn't designed for what we do to it every time we go underwater, and there's always the potential for all those variables to align in a way that's not going to produce a happy outcome. It's a risk we all take every time we go diving.

As Ross Hemingway once put it ... "we're all lab rats" ... anybody who thinks it can't happen to them because they've considered all the variables is kidding themselves.

... Bob (Grateful Diver)

I should have said, "the guy who is overweight and out of shape who gets bent is always like 'i have no idea how this could have happened'"

It's not that everyone who gets bent is overweight. There's always SOME reason. Photo shoot for ADM in the Bahamas? Did anyone drink? Have something bad to eat? Many factors contribute to possible causes... yes?

 

[MXGratefulDiver]

I should have said, "the guy who is overweight and out of shape who gets bent is always like 'i have no idea how this could have happened'"

It's not that everyone who gets bent is overweight. There's always SOME reason. Photo shoot for ADM in the Bahamas? Did anyone drink? Have something bad to eat? Many factors contribute to possible causes... yes?

I agree with you that there's always a reason ... we just don't always know what it is.

Even those who understand DCS the most don't have all the answers ... and for that reason, I prefer to consider them "unexplained" rather than "undeserved". By virtue of the fact that we chose to go diving, we deserve the consequences of the risks associated with diving ...

... Bob (Grateful Diver)

 

[Rhone Man]

I think people sometimes try to over-rationalise DCS. If a large population is exposed to radiation, some will grow cancerous tumours (although not all the same type of tumours) and some will not - no one thinks that is weird. There is just an inherent randomness at the biochemical level that means you can only boil it down so far.

 

[Duke Dive Medicine]

Greetings all. I was invited to the forum by John (Cave Diver) and hope that I can contribute a few things without mucking up the waters.

Regarding PFO detection: Transthoracic echo with bubble contrast is sufficient to detect a clinically significant PFO, and that's typically what we order when we want a diver tested for it. However, it has to be with bubble contrast. TTE alone won't do. Color flow doppler in the hands of a good technician can also detect a PFO, though I've recently corresponded with someone who took a forceful valsalva to shunt with the bubble contrast but shunted at rest on the color flow doppler. Transesophageal echo can detect PFO without bubble contrast but is more invasive and expensive. Trancranial doppler detects bubbles in the temporal artery, which presumably means that someone with a high venous bubble load has shunted, but that doesn't necessarily mean that the diver has a PFO. A PFO or other atrial septal defect is not the only way to shunt bubbles. It's been shown that, in a healthy individual, bubbles can shunt through the pulmonary circulation with exercise. Shunts can also exist in the mesentery (the tissue that holds the small bowel in place).

The irony is that in most divers, PFO is not normally tested for until after a DCS incident (though many of the posters here have been tested without such an incident). Even still, the question remains whether the DCS was as a result of the PFO. There is a positive correlation between certain types of DCS (severe neurological hits, inner ear DCS, and maybe type II skin bends) and PFO, but that's about all we know. There are reports of bubbles being observed to cross a PFO in some studies - it happened to one of our flying after diving study subjects at altitude. We immediately took the chamber back down to sea level and the subject didn't suffer any ill effects.

Re PFO repair: our current position is that for the majority of recreational divers, the risk of side effects from the repair is higher than the risk of diving with a PFO. However, I've recently been corresponding with our head of interventional cardiology, who told me that he hasn't seen any adverse effects in anyone with a PFO repair performed at Duke in the ten years he's been here. At any rate, we counsel divers with a PFO who choose to continue diving to do so very conservatively (i.e. well within the no-d limits), and recommend that they consider diving nitrox on air tables. Ultimately, though, we leave it up to the diver whether to have the defect repaired or not. Clearly, the more provocative the dives, the more likely the diver is to have a high venous bubble load and the more likely he/she is to shunt, so in a deep tech diver, repair of a PFO may be more appropriate. Currently, the Navy tests anyone who suffers a DCS hit and disqualifies them from diving duty if they're found to have one.

Re bubbles and the immune response: any foreign object in the circulation will activate the inflammatory/immune responses. A bubble resting against the endothelium (lining) of a blood vessel will cause irritation, which activates the inflammatory cascade, which causes leukocytes (white blood cells) to adhere to vascular endothelium. These leukocytes release more inflammatory mediators which ultimately cause the blood vessel to become porous and leak and possibly develop a clot. The longer the bubble is there, the more this progresses and the harder it is to reverse, which is why it's important to seek treatment for DCS early. One of the benefits of hyperbaric oxygen is that it interferes with the molecule (beta II integrin) that allows the leukocytes to adhere to the endothelium, so it helps interrupt the inflammatory cascade.

I disagree with the position that everyone who gets DCS "deserved" to get it through some oversight, inaction, or inappropriate action. Yes, there are some cases where this is true, and we all have stories about such folks. However, it's entirely possible for a healthy, well-hydrated, well-rested triathlete to get bent on his first dive of a series despite following his computer or tables to a T. Maybe he shunted through his pulmonary circulation, or maybe it was just his day. The fact remains that the risks of DCS go up with depth and bottom time no matter what deco algorithm is used. Gene Hobbs and Keith Gault presented a poster at UHMS last year that demonstrated this using commercially available deco software, and we're working on expanding this research right now. The poster should be ready to go for this year's UHMS conference.

For what it's worth, we also use the term "unexplained" vs. "undeserved" because it takes some of the judgmental tone out of it. I think that one reason many divers don't seek treatment for DCS is the stigma that's attached to it, i.e. you got bent, therefore you must be an idiot. We've found that to be (generally) untrue, and we don't treat DCS like a "stupid" injury, we treat it like an athletic injury, because in the vast majority of divers we see, that's what it is. Hopefully one day we'll have a complete biochemical/biophysical explanation of DCS, but we're not there yet, so it might be best to reserve judgment (and hopefully some education leading to behavior change) for those who really need it.

Best regards,
Eric Hexdall, RN, CHRN
Clinical Director, Duke Dive Medicine

 

[LiteHedded]

Greetings all. I was invited to the forum by John (Cave Diver) and hope that I can contribute a few things without mucking up the waters.

Regarding PFO detection: Transthoracic echo with bubble contrast is sufficient to detect a clinically significant PFO, and that's typically what we order when we want a diver tested for it. However, it has to be with bubble contrast. TTE alone won't do. Color flow doppler in the hands of a good technician can also detect a PFO, though I've recently corresponded with someone who took a forceful valsalva to shunt with the bubble contrast but shunted at rest on the color flow doppler. Transesophageal echo can detect PFO without bubble contrast but is more invasive and expensive. Trancranial doppler detects bubbles in the temporal artery, which presumably means that someone with a high venous bubble load has shunted, but that doesn't necessarily mean that the diver has a PFO. A PFO or other atrial septal defect is not the only way to shunt bubbles. It's been shown that, in a healthy individual, bubbles can shunt through the pulmonary circulation with exercise. Shunts can also exist in the mesentery (the tissue that holds the small bowel in place).

The irony is that in most divers, PFO is not normally tested for until after a DCS incident (though many of the posters here have been tested without such an incident). Even still, the question remains whether the DCS was as a result of the PFO. There is a positive correlation between certain types of DCS (severe neurological hits, inner ear DCS, and maybe type II skin bends) and PFO, but that's about all we know. There are reports of bubbles being observed to cross a PFO in some studies - it happened to one of our flying after diving study subjects at altitude. We immediately took the chamber back down to sea level and the subject didn't suffer any ill effects.

Re PFO repair: our current position is that for the majority of recreational divers, the risk of side effects from the repair is higher than the risk of diving with a PFO. However, I've recently been corresponding with our head of interventional cardiology, who told me that he hasn't seen any adverse effects in anyone with a PFO repair performed at Duke in the ten years he's been here. At any rate, we counsel divers with a PFO who choose to continue diving to do so very conservatively (i.e. well within the no-d limits), and recommend that they consider diving nitrox on air tables. Ultimately, though, we leave it up to the diver whether to have the defect repaired or not. Clearly, the more provocative the dives, the more likely the diver is to have a high venous bubble load and the more likely he/she is to shunt, so in a deep tech diver, repair of a PFO may be more appropriate. Currently, the Navy tests anyone who suffers a DCS hit and disqualifies them from diving duty if they're found to have one.

Re bubbles and the immune response: any foreign object in the circulation will activate the inflammatory/immune responses. A bubble resting against the endothelium (lining) of a blood vessel will cause irritation, which activates the inflammatory cascade, which causes leukocytes (white blood cells) to adhere to vascular endothelium. These leukocytes release more inflammatory mediators which ultimately cause the blood vessel to become porous and leak and possibly develop a clot. The longer the bubble is there, the more this progresses and the harder it is to reverse, which is why it's important to seek treatment for DCS early. One of the benefits of hyperbaric oxygen is that it interferes with the molecule (beta II integrin) that allows the leukocytes to adhere to the endothelium, so it helps interrupt the inflammatory cascade.

I disagree with the position that everyone who gets DCS "deserved" to get it through some oversight, inaction, or inappropriate action. Yes, there are some cases where this is true, and we all have stories about such folks. However, it's entirely possible for a healthy, well-hydrated, well-rested triathlete to get bent on his first dive of a series despite following his computer or tables to a T. Maybe he shunted through his pulmonary circulation, or maybe it was just his day. The fact remains that the risks of DCS go up with depth and bottom time no matter what deco algorithm is used. Gene Hobbs and Keith Gault presented a poster at UHMS last year that demonstrated this using commercially available deco software, and we're working on expanding this research right now. The poster should be ready to go for this year's UHMS conference.

For what it's worth, we also use the term "unexplained" vs. "undeserved" because it takes some of the judgmental tone out of it. I think that one reason many divers don't seek treatment for DCS is the stigma that's attached to it, i.e. you got bent, therefore you must be an idiot. We've found that to be (generally) untrue, and we don't treat DCS like a "stupid" injury, we treat it like an athletic injury, because in the vast majority of divers we see, that's what it is. Hopefully one day we'll have a complete biochemical/biophysical explanation of DCS, but we're not there yet, so it might be best to reserve judgment (and hopefully some education leading to behavior change) for those who really need it.

Best regards,
Eric Hexdall, RN, CHRN
Clinical Director, Duke Dive Medicine

thanks for the post!

 

[The Chairman]

I think what we need to do is just throw the term "undeserved" into the garbage can because we don't really know what is deserved and what isn't.

I prefer to call them "unexplained."

Who really "deserves" a hit? Maybe someone like Hitler, but for the most part, divers aren't trying to earn a DCS hit just like no one deserves cancer or a heart attack.

2. We don't know what the "rules" are

It's not that we don't know the rules... it seems that the ones we know are good to know and in actuality, very, very few peeps get DCS diving within tables and PDCs. What we don't understand are all the mitigating factors.

 

[karstdvr]

. However, it's entirely possible for a healthy, well-hydrated, well-rested triathlete to get bent

Intersting that you mention hydration,when I understand a lot of research shows this plays less of a role than once thought.