Free Diving and DCS

[Liquid]

There's also no hard evidence connecting cancer and smoking, and a million other things that are taken for granted. Does it make smoking cigarets healthy!?

I am no factbook, I can't recall everything. Like I said- From what I was tought, As well as from working with all sorts of diving models (which by no means are reall tissues on reall people, only imaginary tissues on a PC) I have an absolute answer and it is the one I gave. Not everything is researchable, and not everything that IS researchable is worth researching, as some things are left to comon logic (You can reasearch what are the likely outcomes of shooting oneself in the head, but I am certain that some pure logic will give a good answer here!!!).

If you studdied some modern physics, you probobly know that a lot of it is based on moddels that where not vrrified in a test, since they can not be tested (at least not in today's technology, and probobly not for some years to come). If you know about Schrawdinger's cat, you should have a nice reason for it.

One last thing I am wondering about- Aside from shouting "Gewald" (I don't know what it really means, but it's a word in yedish, that is like screaming someone is wronging you or something like that ) will you personnaly go and free dive right after you go out of a scuba dive or do you just like to argue?

 

[art.chick]

Great discussion of DCS & freediving! One risk to freedivers is "shallow water blackout." That is not a risk on scuba.

 

[Liquid]

That's very true art.chick. However this has nothing to do with DCS, and everything to do with hyperventilating before the dive, in order to create a low amount of CO2 in the blood which will enable to dive longer.

 

[Dr Deco]

Dear Readers:

There seems to be constant interest in the topic of combining free diving and scuba diving. Regrettably, there is no laboratory data on this subject. It seems to be frequent enough, and unaccompanied by DCS problems, that it one would get the impression that it is quite safe. That is essentially “proof from field data,” and implies that the divers themselves have been there own test subjects. While such may seem grossly unappealing to many, that does appear to be the bottom line.

Laboratory experiments with animals does suggest that the lung capillaries are very good filters for gas bubbles, and that they do not penetrate into the systemic arterial system. The arrangement of these capillaries is such that they serve a purpose of filtering. In the natural world, most likely this takes the form of small blood clots. For divers, bubbles are also filtered. Therefore, diving when you have gas bubbles in the venous circulation does not mean that you will find these in the arterial circulation (and brain and spinal cord) if you are recompressed.

Divers, however, must always be mindful that these “facts” are generalities, and that they may not hold in all cases. This means that some divers have reported serious problems in individuals performing free dives following scuba. That this cannot be explained is not to imply that we should disregard the report. An explanation might involve the fact that these individuals had venous bubbles, a PFO, and experienced fluid shifts while underwater (increased preload).

I would personally be leery of much free diving before or after scuba.

Dr Deco
:doctor:

 

[pescador775]

Freedivers/spearos often spend considerable time, up to 4-5 hours, swimming, getting chilled, fatigued and dehydrated, and building up N2. If the hunting has been good and there have been no "close calls" the freediver may not even notice or care that he is tired. For these reasons, especially with respect to the dehydration, they seem to be at increased risk for bends after a subsequent tank dive.

The case of freediving after SCUBA is somewhat different. Freediving to SHALLOW (30') depths after a surface interval is a good way to wind down and should be harmless. I know of no problems from personal experience. I can't see a theoretical issue with this either provided the above precautions are followed. It would be interesting if data had been compiled on this. I imagine some chamber operators would have anecdotes concerning these practices.

I completely agree with Dr Deco's description of the possible variables which might raise safety issues with either.

 

[Chief Chris]

Taravana, a condition first observed by E.R. Cross in 1958, and reported in 1958- is a diving syndrome seen in working Tuamotu Island natives diving the Takatopo Lagoon. The word apparently means 'to fall crazily' and is thought to represent decompression illness in these divers. P. Paulev, a Danish naval officer described his own personal experiences with DCS from breath-hold diving in 1965.

I would worry about this. For the most part it won't happen. But has been reported.

 

[sheck33]

Liquid once bubbled...


1) Actualy- there's a solid answer to the shalow than deep/deep than shalow quesion-and it's Deep than shallow. why? for a very simple reason- The dive tables are based on calculations that one of their factors is that every dive is as deep as the last one or shalower, but never deeper. Do it otherwise, and you change the algorithm. I worked a bit with some formulas and saw how it affects the tissues.

no there is not a solid answer to that question. And this ALWAYS do your deep dive first is lowest common denominator BS. I am not saying ALWAYS do your deep dive last BUT the order in which you do it is not an issue PROVIDED you decompress correctly to begin with. And doing my second dive deeper doesnt change the algorithm, the algorithm doesnt care what order you do dives in.
That is one of the problems with these, and all, models. Models also dont know whether you are a smoker or overweight or have some other problem.

People also get taught NEVER hold your breath. BS again, what student divers should hear is WHEN it is ok to hold your breath and when it is not and WHY.

a nice example: dive to 300ft for about an hour followed by a dive to 300ft for about an hour with a 1-2 hr SI. According to all these beautiful models & tables they should be dead right? they'r not..

 

[The Iceni]

pescador775 once bubbled...
At surface pressure the amount of dissolved nitrogen in the human body is about one liter. Borrowing from classical Haldanian theory and Henry's law, this amount can be doubled to about two liters without subsequently incurring DCS. However, the human lungs, when inflated to maximum, contain approx 4 liters of nitrogen. I think you get the picture.

For example, if you could freedive to depths of 100 feet or more, and hold your breath for 30 minutes, you would get the bends, in my opinion.

Hi Pescador,

We all know that few humans can hold their breath for very long, certainly not for thirty minutes.

As Dr Deco has already pointed out there is no reliable experimental data so it is difficult to seperate myth from what is theoretically possible in the scenario of mixing scuba and free-diving. I also support what liquid posted.

I like to go back to first principles when analysing such questions. I think I am right in making the sweeping statement that DCI cannot develop unless a sufficient amount of excess inert gas has dissolved in the tissues. I am not sure it is wise to look at the volume of dissolved inert gas, Pescador. Perhaps it is better to look at its effective partial pressure, which is what Haldane et al. really did.

DCI can develop (on surfacing and the release of pressure) if sufficient inert gas has earlier been forced into solution in the tissues under the pressures generated by (scuba) diving; - There must be both an increased pressure AND a continuous supply of inert gas at that pressure.

Free divers do indeed expose their alveoli to increased partial pressures of nitrogen on every dive and Pescodaor is quite correct that this gas will dissolve in the peripheral tissues. This movement of inert gas into (and out of) solution will continue until a state of equilibrium is reached and the effective partial pressure of the gas in solution in all parts of the body equals that in the lungs.

Unless the free diver spends more time underwater that he does recovering on the surface after each of his dives I aver DCI can never occur in free divers; -

Solubility

Say on the surface your lungs do indeed contain 4 litres of nitrogen at 1 bar. If you instantaneously free- dive to 30 metres (say 100 fsw) the alveolar pp N2 will rapidly increase to 3.2 bar but because nitrogen rapidly dissolves in blood (it's half life is in seconds) the ppN2 of the blood will rapidly rise towards 3.2 bar but - and this is the important point - the alveloar ppN2 will fall in proportion to the amount of gas removed from the lungs by solution in the blood (Of course, this depends on the solubility of nitrogen in blood, which I will look up later).

However, in scuba, the alveolar pp N2 will remain at 3.2 bar because whatever nitrogen taken from the alveoli is continuously being replaced by the regulator - under pressure.

Tissue half -times

This concept is much simpler to grasp. It takes time for inert gas to dissolve in the body's tissues and a free diver is simply not exposing most tissues to long enough exposures to approach their half-times, let alone the state of equilibrium (approx six half times)

Thus the tissue pp N2 can never reach 3.2 bar in 30 metre free divers, even after a theoretical thirty minute dive.

Any point to this?

I do not believe that free-divers run a serious risk of DCI because they can never dissolve sufficent inert gas in the compartments that matter although other factors, including bubble dynamics may play a part here. On the other hand free-diving after suba could be hazardous because this flaunts at least two basic rules of scuba diving;-

1) Free divers undertake yo-yo profiles.
2) They perform very rapid ascents (with no safety stop!)

Even after a routine no-stop dive the faster tissue compartments will contain gas in the liquid phase approaching saturation, and decompression does not stop on surfacing.

So from this armchair (and with no experimental data whatsoever)I suggest that, as a rule of thumb, it would appear to be safe to free dive before scuba but post dive free-diving ought to be avoided at least until it is safe to fly.

 

[pipedope]

If you want information from real world experience read;

http://www.wkpp.org/articles/Decompression/why_we_do_not_bounce_dive_after_diving.htm

Real world experience trumps theory every time.

 

[Frank O]

Dr Paul Thomas once bubbled...
I do not believe that free-divers run a serious risk of DCI because they can never dissolve sufficent inert gas in the compartments that matter although other factors, including bubble dynamics may play a part here.

Apt comments, and in fact DCS is not common among freedivers. However, there have been some notable cases among relatively advanced breath-hold divers who follow aggressive schedules spending considerable cumulative time at significant depths. In particular, I remember that the Canadian freediving coach Kirk Krack told us when I took one of his clinics last spring that a German freediver of his acquaintance got a very serious bends hit after spending a good part of a day freediving with a scooter. This fellow apparently was going up and down and up and down, to depths quite a bit over 100 ft -- but was only freediving, with no scuba involved. I wouldn't be surprised if, all told, his bottom time exceeded his surface recoveries. If memory serves correctly, the outcome of the incident was that he was in a wheelchair for several months. So, although rare, it does happen!