"Undeserved" DCS hits

[ianr33]

Statiscally, that's true. But getting back to my OP, do you believe it's inevitable, or avoidable?

Both!

You learn as much as you can, and do your best to reduce the probability of getting hit. But that probability is never going to be zero.

 

[Chatterton]

So, what do we use to calculate decompression? Maybe you are all table oriented, or maybe you have the latest dive computer, I don't know, but it doesn't matter. They all use a thing called "mathematical calculations". This math stuff gives us an estimation of what I will call a, "biological process" that involves molecules.

The dive profiles we use, provide us with estimations of the biological process going on in our bodies, without the input of biological considerations like cardio pulmonary efficiency, physical exertion, anxiety, thermal considerations, and overall organism fitness.

Let us say, that we have two identical divers making two identical dives with the same equipment. Diver 1 uses 2500psi of gas, while Diver 2 uses 1500psi of gas. So, Diver 1 breathed more gas, specifically more molecules of inert gas? So, would it not follow that Diver one had more molecules of inert gas in his/her body to get rid of? Duh????

This is not about what we don't know about decompression physiology, it is about how we can calculate the complicated biological process of inert gas loading and unloading? the simplest and cheapest way is to estimate using time and pressure? It is up to the diver to interpolate this information based on unique aspects of each and every individual dive. How much gas did I use? Should I decompress more or less than indicated by the estimate provided by my computer/table?

The jackass that says he has had an "unearned hit" is laying a firm foundation for the next time he/she gets bent, because they need to soothe their bruised ego instead of taking responsibility for screwing up, misinterpreting their dive, and actually learning something that they can use on future dives.

If you have a PFO, you have a PFO and you need to get it fixed an/or quit diving.

If you are overweight, out of shape, don't have experience, don't know anything about diving physiology, and are diving beyond your capabilities, then you come to me with some story about an "unearned hit", I am going to suggest you stop diving and take up bowling or knitting before you kill yourself.

Seriously. Political correctness in diving is absurd, and so is this "unearned hit" crap. Only a Total Dumb Ass of the first order uses this as his/her excuse.


Cheers

 

[Tortuga68]

It seems so far we all agree that there's no such thing as an 'undeserved' hit ie if you got bent then you did something wrong, knowingly or otherwise

What about the other end of the spectrum - the people who break/bend some or all of the 'rules' and get nothing except a rueful grin... I think we all know, know of or have heard of someone like that - people that breathe their travel gas for the entire BT, or switch to oxygen at 21m on deco instead of 50 mix (these are two examples I know of personally) and not only live to tell the tale but don't even get symptomatic

Why do you think rec divers are getting bent and not these people? Luck, personal tolerance, love of jesus - something else?

 

[boulderjohn]

I think it's agreed that multiple dives over several days put you outside of prevalent deco theory ie tables, is that the reason for these hits?

According to DAN research published a couple of years ago, roughly 80% of DCS occurs on the first day of diving, and roughly 80% of those cases occur on the first dive.

 

[boulderjohn]

Let us say, that we have two identical divers making two identical dives with the same equipment. Diver 1 uses 2500psi of gas, while Diver 2 uses 1500psi of gas. So, Diver 1 breathed more gas, specifically more molecules of inert gas? So, would it not follow that Diver one had more molecules of inert gas in his/her body to get rid of? Duh????

I asked a similar question a number of years ago in the Ask Dr. Decompression forum and got a resounding "no."

You inhale and you exhale. While what you inhale is in your lungs, it can diffuse into your blood at a rate consistent with the gas laws. Then you exhale and that which did not diffuse goes away. Then you inhale and we start again. Inhaling and exhaling at different rates will make very little difference in the amount of diffusion. A diver who goes through air more quickly than another will have a slightly richer mix of nitrogen in the lungs at any given time, but it is not a big difference. Most of the excess nitrogen inhaled is exhaled into the ocean and does not diffuse into the blood and then the body.

It comes down to the gradient between the partial pressure of the gas in the lungs in comparison to the partial pressure of the gas in the blood. The rate at which the PP in the lungs is replenished will have only a marginal difference.

 

[Cave Diver]

According to DAN research published a couple of years ago, roughly 80% of DCS occurs on the first day of diving, and roughly 80% of those cases occur on the first dive.

Was that attributed to anything specific? Stress of traveling, including fatigue, dehydration, etc? Or was there even any distinction made on whether local vs. travel dives?

There may also be a simple intracellular process in DCS -- I had a chance to talk to some NEDU guys last year who were doing some cellular research that implied this might be true.

A little above my head, but I'll jump in with a question anyway. Would that give any indication on whether immune systems would play a part in DCS?

 

[Tortuga68]

BJ, thanks for sharing your thoughts on what isn't a relative cause of DCS in divers with different RMVs

Could you extrapolate that into an opinion on whether there is such a thing as an undeserved DCS hit?

 

[boulderjohn]

Was that attributed to anything specific? Stress of traveling, including fatigue, dehydration, etc? Or was there even any distinction made on whether local vs. travel dives?

They had no idea. All they had was the data.

 

[boulderjohn]

BJ, thanks for sharing your thoughts on what isn't a relative cause of DCS in divers with different RMVs

Could you extrapolate that into an opinion on whether there is such a thing as an undeserved DCS hit?

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."

I just went to the thread that brought up the topic. If I had to bet, I would say she did not have DCS at all. I would bet she had a lung overexpansion injury. Her dives were all well within recreational limits. What was not normal was her rapid ascent to the surface from depth. After the dive she felt a choking sensation, a common response in certain cases of lung overexpansion injuries.

If that is the case, I would use the word "deserved."

 

[ianr33]

According to DAN research published a couple of years ago, roughly 80% of DCS occurs on the first day of diving, and roughly 80% of those cases occur on the first dive.

Do you recall if the paper included the denominator?

If 99% of all dive "trips" were only one day long then the fact that 80% of DCS cases occurred on the first day of diving would indicate the first day is actually safest.