Can freediving cause DCS?

[trux]

Another problem that I did not see addressed in any documents, is the impact of diving response on the DCS risk. At breath-hold diving, due to the vasoconstriction and blood shift, the blood pressure in the core and in the brain raises. That effect may be further amplified by involuntary diaphragm contractions. When you then surface and start breathing, the cardiovascular responses normalize after a while. That means the blood pressure difference in the core and in the brain may add to the pressure gradient profile from the dive itself (similarly as flying after diving, though likely not to the same extent), and I imagine it may amplify the nitrogen bubble creation.

Please note that this is my personal speculation, not based on any scientific study, but it is something not discussed in common scuba diving hyperbaric medicine, because it is not relevant there. It is a question whether it was considered and examined by freediving experts - so far I did not find any references to such studies.

 

[efattah]

For those who claim that most cases of DCS are 'misdiagnosed', consider some of my history:

DCS Episode #1: Wreck diving trip to HMCS Chaudiere in BC. I did 9 dives to 20 to 38m, average dive time 2'44", average surface interval 6'30", which was following the table presented to me by Kirk Krack, a table which was created by a diving physician. Immediately upon exiting the water, Dr. Potkin (DCS expert himself) did a tearfilm analysis, and about 8 minutes later my symptoms began. I explained each symptom to Dr. Potkin and he reviewed my profile. He concluded I was suffering DCS and I was put on 100% O2 immediately. This was despite the fact that I was following the freediving table presented to me.

DCS Episode #8: After suffering severe DCS symptoms at Ansell Pt, I went to the hyperbaric facility at the Vancouver General Hospital. There, TWO experts in DCS/hyperbaric medicine diagnosed me with freediving DCS and immediately put me in the chamber on Navy Table 6. Upon descent to 20m on 100% O2, almost all symptoms disappeared. Symptoms gradually reappeared (less intensely) during the reascent to 0m, which took many hours. Once again I had been diving following the previous 'table', which was now clearly inadequate (at least for me).

 

[efattah]

Herbert Nitsch suffered a tremendous DCS hit during a spearfishing trip. He did 15 dives to 35-45m, 2'30" to 3'30" long, with 6'30" intervals. Upon getting out of the water, he suddenly collapsed and his whole body was paralyzed. He was carried to a recompression chamber where he recovered.

 

[unobreath]

For those who claim that most cases of DCS are 'misdiagnosed', consider some of my history:

DCS Episode #1: Wreck diving trip to HMCS Chaudiere in BC. I did 9 dives to 20 to 38m, average dive time 2'44", average surface interval 6'30", which was following the table presented to me by Kirk Krack, a table which was created by a diving physician. Immediately upon exiting the water, Dr. Potkin (DCS expert himself) did a tearfilm analysis, and about 8 minutes later my symptoms began. I explained each symptom to Dr. Potkin and he reviewed my profile. He concluded I was suffering DCS and I was put on 100% O2 immediately. This was despite the fact that I was following the freediving table presented to me.

DCS Episode #8: After suffering severe DCS symptoms at Ansell Pt, I went to the hyperbaric facility at the Vancouver General Hospital. There, TWO experts in DCS/hyperbaric medicine diagnosed me with freediving DCS and immediately put me in the chamber on Navy Table 6. Upon descent to 20m on 100% O2, almost all symptoms disappeared. Symptoms gradually reappeared (less intensely) during the reascent to 0m, which took many hours. Once again I had been diving following the previous 'table', which was now clearly inadequate (at least for me).

I don't disagree that you suffered DCS as a treatment table 6 is used for DCS type 2. But I was more referring to some of the guys that have posted getting 3 DCS hits while spearfishing. As they do not have a doctor there to do a doppler or tear film sample, or even a blood sample. The only way to treat DCS is a recompression chamber. 100% 02 on surface is good but the chance of still having nerve damage is quite possible and more than likely.

As for the high CO2. CO2 headaches are not fun, but are extremely possible in freediving. I am sure we have all experienced them but high CO2 doesn't contribute to DCS as DCS involves inert gases like nitrogen. A headache is probably the biggest problem with CO2 besides BO.

 

[trux]

I am sure we have all experienced them but high CO2 doesn't contribute to DCS as DCS involves inert gases like nitrogen. A headache is probably the biggest problem with CO2 besides BO.

That's a mistake coming from you being a scuba guy and having little background in freediving physiology. Any gas that is not being consumed or removed by the metabolism, and is dissolved in liquids or fats, will create bubbles during decompression. Although CO2 dissolves very well in liquids and would be so a dangerous decompression gas, it is normally not an issue, because it is being bind and transported away by hemoglobin. At high acidosis (after a prolonged apnea), the evacuation effect of hemoglobin is limited, so less CO2 will be removed from the body and more bubbles will be produced. It is true that the bubbles will be quickly consumed by the metabolism as soon as you start breathing normally and hemoglobin starts transporting efficiently, so they are not of a such concern like nitrogen bubbles after the surfacing, but I believe that at freediver it may aggravate / amplify a nitrogen DCS to a higher degree than it would be at an aerobic (scuba) diver.

Besides it, headache is far not the only risk CO2 poses, even if we dismiss the above DCS effect as a pure speculation. CO2 retention seriously increases the risk of oxygen toxicity and also nitrogen narcosis. Besides it, it has narcotic and toxic effects itself and in extreme cases may lead to a blackout.

 

[apneaboy]

CO2 acts as a capillary dilator which increases the uptake of inert gases such as Nitrogen so would contribute to DCS I believe. As well as increase the toxic effects of Oxygen and narcotic effects of Nitrogen at depth.

 

[cdavis]

You folks have gotten way beyond my level of expertise, but shouldn't there be a difference in bubble formation between an inert gas like nitrogen,(N2) which dissolves in the blood without changing chemical form and a chemical like C02 that ionizes and forms an acid in the blood, no longer C02 gas, but something else?

Connor

 

[trux]

You folks have gotten way beyond my level of expertise, but shouldn't there be a difference in bubble formation between an inert gas like nitrogen,(N2) which dissolves in the blood without changing chemical form and a chemical like C02 that ionizes and forms an acid in the blood, no longer C02 gas, but something else?

The main reason CO2 is (normally) not a problem, is that it is chemically bound to hemoglobin (at least a significant part of it). The part that dissolves in blood and other body liquids is similar to CO2 dissolved in soda (or beer) - it also changes the pH of the liquid, but will still make hell of bubbles when you depressurize it (decapsule the bottle).

 

[Lockedin]

Might be a non-issue, but I (as most non-professional SCUBA divers) were taught that breathing a compressed gas at depth, and then ascending too quickly (big over simplification, I know). As many other spearos, I believed that since I was on a surface breath, DCS was not an issue.

My question (for those with bigger brains than I):

1. Do freedivers lungs compress the air internally (especially at depth)? It seems that packing would!:naughty
2. And do contractions further compress air?

Very interesting discussion! The heat that's been generated (great job monitoring, Sanso & BennyB!), should be taken as an indicator of passionate interest, and minds at work. Just try to be civil! Not to get religious (yet another heatable topic ), but:

As iron sharpens iron, so one man sharpens another. Pr 27:17

 

[bass hunter]

Hi guys,im fairly knew to freediving and dont know that much about the safety aspects as regards getting "the bends".
Realisticaly how deep would I have to dive to get it,or is it more the case of surfacing too quickly from any depth.

 

[cdavis]

Hi Richie,

Basically, if you are fairly new, I wouldn't worry about it at all. DCS is something that seriously deep divers need to consider, like 30 m +, usually a whole lot +. There is, IMHO, good reason to be aware that some risk exists at lessor depths (say 20 m) if doing repetitive dives of long duration and short surface intervals, not something a non-expert diver is likely to engage in. The only place you might be concerned is if you are doing many dives in 18 m or more and then get on an airplane. Use the search function and you will gain quite a lot of detailed info.

Connor

 

[sanso]

...
Realisticaly how deep would I have to dive to get it,or is it more the case of surfacing too quickly from any depth.

Uhm - have You read this thread?
Do that and You will find enlightenment - or maybe not, but You'll definitely get the picture.

 

[Michael]

I think I may have gotten a DSC hit a couple days ago. I was doing dives to 40M (and because of technical problems with the dive rig we cancelled target dives- which turned out to be a lucky break bc had I done my target dive I think the DSC would've been worse). A couple hours later I boarded an airplane for home. That night, I felt some mild neurological symptoms of DSC, confusion, extreme irritability. It was also after many days of diving every day so I was already fatigued.

 

[cdavis]

I know one other diver who combined a full day of spearfishing, long, 50-60 ft dives with an unpressurized airplane trip on the same day. He got a case of skin bends out of it, so its possible.

Been body surfing lately?

Connor

 

[rafacuatic]

Hello.
A month after my first DSC spearfishing, i meet an hiperbaric doctor and told me that after a bend is easy to have more.
Last week i felt the symptoms after 2 dives to 60 m with more than 15 min interval.
It is a good idea to breath o2 at 5m for sometime after the dive?
Rafa

 

[David Goh]

One question to all: have you tried using a dive computer during your freediving, and do you think it would contribute to increased safety and possibly DCS avoidance?

After having watching the market for some years, I only finally plunked down some money to buy the Oceanic GEO dive computer for my own safety: dive computers have been around for ages, but it is only recently that dive computers with free-diving modes have shown up, and even more recent are dive computers that support computation of nitrogen loading profile for both scuba and freedive.

After reading about the DCS hits, I still have my concerns that the computations may not be adequate for freedivers who have been diving in a certain way and been hit, and may need further tweaking by the manufacturers.

There is an "extra-conservative" mode on the Oceanic Geo, and I'm seriously considering turning this on, even though I'm not sure what alarms might be triggered during freediving ascents if this was activated...

I think sufficient practical usage is needed by frequent deep-diving freedivers to validate that such computers are of value to DCS avoidance in freediving.

I'd be interested to find out if those that got hit with DCS would consider using one of these computers and the next time they get hit, perhaps extract the profiles of the preceeding dives that lead up to the hit, and share this information with DAN for further study into the DCS-Freediving link...

Cheers,
David
Singapore

 

[ricki]

I have some limited experience with the Geo, some recent comments from another forum appear below:

I also picked up a Oceanic Geo. The display and normal functioning
seem to be good. I would urge caution with regard to the free
diving deco meter function however. The deco algorithm my need more
evaluation and development for free diving. During some scooter free
dives last year I had three high nitrogen alarms from the meter
between 105 and 125 ft.. I only noticed one at the time and picked the
other two up on the video audio track later on. More at:

[ame=http://fksa.org/showthread.php?t=4615]Deeper Scooter Free Diving Video - Cayman Wall - FKA Kiteboarding Forums[/ame]

The alarms happened while cruising around maximum depth of the dives
vs. not during ascent. The ascents weren't unduly fast. I was
observing minimum ten minute surface intervals between dives and
hadn't been SCUBA diving with it in some months. The alarm displays
cleared after staying on the surface for a period of time. By
"conventional" rules of thumb, I shouldn't have been at high risk of
DCS problems in the dives. Then again, how much do we really know
about DCS and free diving, i.e. well tested tables and models? Not
knowing what to think, how to interpret the results I contacted
Oceanic and was asked to send the meter back for evaluation. They
concluded the meter was functioning properly but I got the impression
the free diving deco function uses the SCUBA deco algorithm. The
algorithm may or may not consider some of the unique aspects of free
diving vs. SCUBA diving (potentially multiple short duration dives often
without deco safety stops and short surface intervals).

Also, I think the meter algorithm is supposed to calculate deco for
residual nitrogen resulting from combined SCUBA and free diving. This
is part of the reason I bought it, although I try to put tanks rarely.
Looking into instances of nasty DCS brought on by free diving after
accumulating residual nitrogen from SCUBA I concluded I wouldn't do it
until after I had cleared after at least 24 hours regardless of what
the meter's calculations might say to be on the safe side.

Rick

 

[immerlustig]

hi,

what does the manual say about the deco-meter (?) function in freedive mode?

cheers

 

[ricki]

hi,

what does the manual say about the deco-meter (?) function in freedive mode?

cheers

Beyond meter operation and limited interpretation, not much. A section from the Geo manual appears below:

I also came across a product description:

Advanced Free Dive Mode
The GEO provides accurate depth and time with an amazing 1-
second sampling rate for subsequent PC download and analysis.
Dive Time is displayed in seconds and minutes. Custom audible
alarms include Elapsed Dive Time, Countdown Timer and (3)
Independent Max Depth Alarms. The GEO is the first Free Diving
Computer to calculate and track Nitrogen Tissue Loading, allowing
you to switch between SCUBA dives and Free Dives on the same
dive day.

again, mixing free diving and SCUBA when residual nitrogen may
be an issue seems to be a bad idea from accidents we've heard
about on here. Just because a computer model says something is
OK, is it really OK? Depends, of course.

 

[David Goh]

The tissue model for nitrogen gas absorption is applicable in a hyperbaric situation, whether it is scuba or freediving or even cassion/chamber operations.

The only thing is whether the existing safety parameters i.e. ascent rate, nitrogen loading, etc will be adequate? Would it be necessary to make it even more conservative ensure that those who freedive deeper longer with many more repetitions don't get hit?

Alternatively, it may beg the question of whether some of the freediving practices of individuals needs to be modified to bring them back within the safety margins. Bear in mind that in the 1960s when studies were made, traditional breath-hold divers (fishermen, etc) suffered "taravana" syndrome after making repetitive dives for 6 hours (typically 18 to 20 dives in 2 hours to depths of 130 feet). Clearly the divers did not realise that their practices were causing them to suffer from decompression sickness.

On the other hand the use of a dive computer will at the very least warn the avid freediver that he is putting himself at risk... if he knowingly accepts that risk, then it's his own call.

Cheers,
David.