Decompression sickness in Freediving

Is it possible to have DCS for Freediver? Unfortunately yes…But at the same time, it is quite easy to put the risk at the minimum. At our school, we normally discuss in details this topic at PADI Master Freediver course, so here are our thoughts on this subject…

DCIM101GOPROG0063938.JPGIn scuba diving, when you are breathing compressed air underwater, your body is saturated more and more with Nitrogen (79% of the air is Nitrogen). The chain looks like this – you breathe in the compressed air from a scuba tank and now the pressure of N(Nitrogen) in your lungs more than in your blood, so, it going to your blood. And now in your blood pressure of N is higher than in your tissues, so, it is going to your tissues. Until you have an equal pressure of N everywhere (this is what we call saturation). And when you start coming up, opposite happens. Now pressure of N is smaller in your lungs, so the reverse process is happening – from your tissues N going to the blood and then to your lungs and then you exhale it. But it doesn’t happen that quickly. In some tissues, this process is slower than in others.

So, this is why when scuba divers coming up, they need to do it slowly (in this case N slowly coming from your body with every exhale) and they also need to have a long surface interval between dives (to release as much N from their body as possible before the next dive). And why they can spend the only a certain amount of time on certain depth (not to get too much N to their tissues).

dcs2If they violate these rules, they have a very good chance to have DCS! Without making it too complicated, DCS is when molecules of N combined in your blood (or tissues) in the form of a bubble and can cause very serious damage!

But why it can be an issue for Freediver?
Among the first, spearfishers who were shooting fish relatively deep (around 20 meters) noticed that after the long session they have symptoms which are commonly associated with “bends” (another word for DCS). So, imagine you dive to 20 meters. On the surface, you did big inhale and bring this air (and around 79% of it is nitrogen) to 20 meters, where the pressure is 3 times higher. So, the pressure of any gases inside your lungs (we call it partial pressure) going to be also 3 times higher. If the pressure is going to be higher in the lungs, then it will go to your blood and further to your tissues in the attempt to reach equilibrium. When you start your ascend, the reverse process will take place. But not 100% (some of our tissue need time to release N2). Some N2 will still be in your tissues. Very very small amount. Not a dangerous amount. But then you are going to do 50 dives more to this depth. And now you have much more N2 in your blood. And on your next ascent, it can forms bubbles and this is DCS….

There are also some predisposing factors which can increase the risk of DCS. Let’s name a few

  1. Dehydration
  2. Exercises
  3. High level of CO2
  4. Cold
  5. Not enough surface time

As you can see, spearfisher who is doing a long session with relatively deep dives and DCIM101GOPROGOPR9056.JPGsmall recovery time has a very good chance to get DCS….What to do, if you are spearfisher? Limit duration of your spearfishing session, have enough rest between dives, use appropriate thermal protection, stay hydrated!

Ok, what about DCS for Deep Freedivers?

Let’s say you are one of the most famous Freediver of all time, Herbert Nitsh, and diving not to 20 meters but to 214 meters!! You make a big inhale as possible (don’t forget, around 79% of inhaling air is N2) and put it under a huuuuuge pressure of 21 atm (this is what you have at 200 meters). During your descent, this N2 from your lungs will come into your bloodstream and from there to your tissues.
And now you will start your ascent. It would be No Limit discipline and you are not going to use your muscles for going up (which is very good to reduce the risk of DCS), you are probably also not dehydrate it nor cold (which is also very good)
But you are quite fast for this huge amount of N2, dissolved into your tissues. The bubbles will form. But not big in the beginning. But when you ascent with the constant speed, they are going to increase in size (because the pressure is decreasing). How to prevent it? You need to stop…And this is what Herbert did – he made a first safety stop at 70 meters (for 30 secs) and the second stop at 30 meters (for 60 secs). But the closer you are to the surface more important your speed is going to be. This is why he dramatically decreased his ascent rate after 30 meters (from 3 m/s to about 1 m/s). And this is how he became The Deepest Man on Earth by making a dive to 214 meters!!
But later, when he was trying to beat his own record he lost his conscious on his way up and failed to do all of the above (safety stops and slow down his speed). As a result, massive DCS….Luckily (actually his story of recovery is almost like a miracle) he survived and recovered from it!

But if you are diving not that deep, let’s say to 40 meters; is it possible to have DCS? And the answer is yes… Last year Freediving legend William Trubridge got DCS during his routine training. I mean routine for him but crazy for all of us! Let’s have a look at it

William did 5 dives to 40 meters with “hangs”. Time of each dive was about 1.50, the surface time between dives only 2.15. As a result, after his 5th dive, William felt one of the symptoms of DCS – numbness in his leg. He went to a hospital and took special treatment for DCS there (pretty expensive!).  This story has a lucky end as well, William completely recovered and competing again!

According to him, he done this type of training before (even harder) and never had any problem.

So, what is the problem here and how to avoid it? The dives were not too deep and not too long (especially if you are World Champion). But the recovery time was quite short.

So, if you are just starting freediving – this is a basic advice – DO have long surface intervals. How long? Here a couple of ways how to count it

  1. The time between your dives should be 3-4 times longer than your dive time. For example, if your dive time 30 secs, then have a rest for at least 2 mins
  2. Divide dive time by 5 and the result is a time in minutes. If you dive to 40 meters, have a rest for at least 8 mins.

And be even more conservative – have even longer rest!

A few things which I would you to remember

dcs3First of all – symptoms of DCS. Type 1 DCS – skin rash on shoulders and upper chest, joint and limb pain. Type 2 DCS – peripheral tingling and numbness, unconsciousness, respiratory arrest and paralysis, coughing, feeling of air-starving.

Second – predisposing factors. Obesity, intense exercise less than 12 hrs before diving, age, fitness level, dehydration, injury and illness, alcohol, carbon dioxide, cold. Obviously, scuba diving before freediving is absolutely no-no!

Treatment for DCS – the patient should lay down and breath 100% O2. Transportation to a recompression chamber should be organized as quickly as possible.dcs4

And one more times how to avoid DCS

  • Don’t freedive after scuba diving
  • Have enough surface interval
  • Don’t ascent very fast from the deep dive
  • Reduce the number of deep dives in one session
  • Limit the duration of the dive session
  • Stay hydrated and use an appropriate wetsuit
  • Don’t consume alcohol and don’t do intense exercise before a session

Stay safe, enjoy Freediving and educate yourself about the activity which you love!

 

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