Alexey Vlaskin- Freediving and Brain health

Freediving and Brain health

Freediving is a great for sport and recreation. It is a way of looking inside yourself and it refreshes the mind after a long working day. Generally, as a sport it is very beneficial for freedivers health and habit loop, it helps people stay healthy and in harmony with surrounding nature of the oceans.

Yet as a extreme activity freediving has some risks associated with it. They include different injuries like ear drum rapture, lung squeeze, sinus squeeze, minor cuts of limbs (rocky entrance), decompression sickness, shallow/deep water block out, nitrogen narcosis, major limb/body cuts (beaten by a shark), eyes injuries (eyes squeeze).

Sorting this list by probability of happening and by people’s perception of an issue and we would have two different lists, because generally people overestimate certain risks like be eaten by sharks. Reviewing risks it is important to note recovery periods for them.

In the table below I summarised the most probable issues freediver can have and common terms of recover:

Possible Issue Average recovery time
Shallow/deep water block out Death, no recovery or 1 day if diving with buddy
Decompression sickness Never or several hours, several days
Lung squeeze 2-6 months
Lungs barotrauma (for ex. after packing) 2-6 months
Trachea squeeze 1-3 months
Ear drum rupture 6 weeks – 12 months
Limbs cuts 6 weeks

Although decompression sickness is not the worst thing can happened to a freediver – the issue with DCS is that it might have a hidden nature and it may not be exposed to a diver straight away, unless one is suffering a major incident. In some cases, it takes several days of intensive freediving to realise that nitrogen built up and decompression sickness took place.

Recent research shows that many freedivers in Australia are affected by this issue and sometimes do not pay attention to it. However other research shows that decompression sickness in freediving mostly takes neurological form and may affect freedivers brains and spinal cords. That significant gap between importance of the problem and people perception of it – makes DCS a very dangerous issue for freedivers around the globe.  The goal of this essay it to discuss DCS in depth and see what freedivers should/can do in order to avoid this issue.

Decompression sickness

Let’s start be describing, what is DCS and what forms can it take. Decompression sickness – the bends, also known as decompression sickness (DCS) or Caisson disease occurs in divers or high altitude or aerospace events when dissolved gases (mainly nitrogen) come out of solution in bubbles and can affect just about any body area including joints, lung, heart, skin and brain.

Types of DCS

According to the [8] there two types of decompression sickness:

  • Type I – Simple sickness. Symptoms involve skin rush, muscular pain, most typically joints pain and rarely lymphatic system damages.
  • Type II – Serious sickness. Symptomatically can be mild and may not be perceived as serious. Involves damage in nervous system, spinal cord, brain, pulmonary system, lungs and circulatory problems such as hypoglycaemic shock. Type II DCS sometimes is compared with stroke as it has similar symptoms and treatment.

DCS and Freediving

On early stages of freediving training we are taught that freediving does not cause decompression sickness as a freediver does not breath pressurised air under water. And in the past for many years that was a general theory. A freediver only takes one breath of air (which is about 7 litters) and that amount of nitrogen is too small to cause any issues.


Only on the last course stages like AIDA 4 or luckily Apnoe Australia course B they speak about possibility of DCS to occur to a freediver. But is it a real problem or it only happens to a few elite freedivers who go beyond 100m mark?

I conducted a short research and survey and here are some quotes.

The first one is from the world famous No Limit champion – Herbert Nitsch:

“The original plan was that I would slow down the sled between 100 and 70 meters below the surface on the way back up, and have a one minute decompression stop at approximately 10 meters depth. Because of the blackout due to narcosis (at approximately 100 meters below the surface), I was not able to slow down the sled, and thus it continued on to 10 meters where it stopped as programmed. Fortunately the safety divers brought me right away to the surface. Because this omitted the planned 1 minute decompression stop, the result was serious DCS (decompression sickness), which is equivalent in my case to several brain strokes with severe initial consequences.” 

The second from another well known freediverEric Fattah[2]:

“Since July 2005 (he wrote it on July 2006) I have suffered freediving DCS at least 7 times. On the worst occasion I went into the recompression chamber. Upon entering the chamber and going to 18m on 100% O2, my symptoms disappeared. This year I was doing nothing but FRC diving, starting each dive with about 4-5L of air. I still suffered DCS at least 4 times (i.e. NO packing, not even full inhale!)
After analysing the data, I concluded that the primary risk factor was the ascent rate. Ascending over 1.15m/s, especially in the last 10m, dramatically increased my risk of DCS. With ascent rates of 1.20m/s, I could suffer DCS after just two dives to 40m.”

“Additionally, an extra slow down on last ~25m is due to my new safety precaution regarding DCS (decompression sickness).”Matt Malina [6] (in a private conversation Matt admitted that he suffered DCS in past on his competitive deep dives.)

“It was holiday mode freediving, I did not quite paid attentions to the surface intervals as the diving itself felt very easy. I did many 30m+ drops, slow FIM dives to 30+ and several to 40-50m. As I can tell there were two main reasons for DCS: surface intervals were small as we had a group of 3 and were cycling between dives fairly quickly(may be about 9 minutes for a round; I did to many max dives that day, normally I do not more that 2 (max/submax), that day I did a bit more. In terms of symptoms, that night I had hands tingling and they felt hot. Symptoms cleared in 3 days.” – Jack Hatfield, from the private conversation.

“I had DCS many times and I had all kind of stuff in [terms of symptoms]” – Australian champion, Ant Judge.

As you can see DCS happens to the professional freedivers. In fact, author spoke to many different pro freedivers and did not find anyone who did not experience that. Moreover, if a freediver has a limb cut or lungs injury – he/she can feel it straight away. But if a freediver has regular minor brain damages – it may go hidden, as humans do not have neuron endings in the brain to feel it. That is why many Australian freedivers and spear fishers are perceiving risk of DCS is low and do not pay much of the attention to it.

DCS and Scuba

Freediver are not the only people who can experience DCS, many scuba divers have this on their risk assessment list. However, DCS is Scuba and Freediving may have different consequences and some scientific articles state that DCS in Freediving more likely to have a neurological consequence.

DCS in scuba was heavily studied in the past and as a result there are some clear practices established in order to avoid this issue after scuba diving. There is a great experimental material collected about suffering DCS in Scuba and here there is a list of typical issues which are mostly associated with decompression sickness Type I:

Source: [8].

Symptom Frequency
Local joint pain 89.00%
Arm symptoms 70.00%
Legs symptoms 30.00%
Dizziness 5.30%
Paralysis 1.60%
Shortness of breath 2.30%
Extreme fatigue 1.30%
Collapse/unconsciousness 0.50%

Let’s compare these results with some data collected by DAN organisation from Australian and spear fishermen[11]:

Symptom Percentage
Headache 50
Nausea 50
Dizziness/vertigo 50
Lack of concentration 37.5
Fatigue/lethargy 37.5
Visual disturbance 25
Lacks coordination 25.0
Disorientation 12.5
Speech disturbance 12.5
Vomit 12.5
Paraesthesia 12.5
Join pain 12.5

In fact, DAN has done some great research on DCS in breath hold diving which described in [11]. Data was collected from five groups of people:

  1. Taravana – a condition known in Tuamoto Archipelago in French Polynesia where the BH pearl divers suffered symptoms such as vertigo, paralysis, mental anguish and unconsciousness. They dive to depths from 13-43 meters with bottom time up to 2m:30s and surface intervals between 4 to 10 minutes.
  2. Ama – Japanese breath hold divers which work in the sea on collecting different animals from the sea bottom. Ama divers use variable weight technic to descent to the bottom of the sea.
  3. Spanish – Spanish freedivers who used underwater scooters to travel to the sea bottom during several hours. They have managed to achieve depths of between 25 to 45 meters with breath hold time up to 4 minutes with average 2m:13s. They conducted about 15-20 dives per hour for the period from 3 to 8 hours.
  4. Australian – data collected from Australian spear fisherman using survey.
  5. Competitions – data collected from competitive freedivers.

Here the table that demonstrates the data intersection from all of these five cases(which highlights that typical symptoms related to Type II DCS):


As you can see symptoms in freediving are typically Type II symptoms and that gives us a sense that freedivers some how affected differently than scuba divers. In [11] we found detailed description which is still to be checked by other scientist and doctors.

Mechanism of DCS

Mechanisms for DCI in breath-hold divers have been described (Figure 1) [10]. After deep, repeated dives, bubbles are formed in venous side and travel through the heart to the lungs. Microbubbles can pass through the pulmonary capillaries, but in general these microbubbles are harmless to tissues. An experimental study showed that microbubbles transiently impair the blood brain barrier [9]. At first, we thought the major mechanism of DCI in breath-hold divers was such microbubbles [10]. But from the MRI findings of Ama divers with DCI, we do not now think microbubbles are the major mechanism of DCI. Since Ama divers have large cerebral infarcts in arterial branches, we should consider other factors as major mechanisms of DCI. Large or small bubbles are normally retained or trapped at small pulmonary arteries or pulmonary capillaries. When Ama divers reach to the bottom, we think that bubbles ‘trapped’ at the lung are compressed and easily pass through pulmonary capillaries. Such bubbles passing through the lung enlarge at the surface and the bubbles induce cerebral arterial gas embolism. In addition, there is a possibility microbubbles are related to trapped bubbles. 

Figure. 1


Competitive freedivers

Again – [11] – has a very interesting article about five competitive freedivers brain examination. Here is the results of their research: “The long term consequences of repetitive breath-hold diving on the central nervous system are unknown. Other investigators have noted brain imaging abnormalities in symptomatic breath hold divers with abnormalities on neurologic exam. We performed brain imaging on five asymptomatic breath-hold divers with multiple breath-hold dives to depths exceeding 30 m [98 ft] over a period of over five years. At the time of brain imaging, neurologic symptoms, physical examinations and brain MRIs were normal. However, brain SPECT scans were abnormal in all five divers. Repetitive breath- hold diving may be associated with asymptomatic brain function abnormalities.”

This logically creates a suggestion that competitive depth freedivers should regular (once a year) do MRI examination of their brains in order to track any abnormalities.

Typical scenarios of DCS

  1. Repetitive freediving.
  2. Deep freediving.
  3. Freediving or spearfishing using artificial mean like scooters (for Spanish freedivers) or variable weights for Ama divers in Japan.
  4. Freediving after scuba. (For the sake of this essay we are not going to talk about the last one as it is obvious preventive mean by not freediving within next 12 hours after scuba diving.)

Key factors

There are certain key factors that may lead or may prevent freediver from having a DCS. It is very important to consider those factors when contemplating your freediving plan.

  1. Surface interval. If it is not big enough, Nitrogen builds up in tissues. AIDA recommends using “rule of thumb”. For dives below 30m, use depth / 5 = minutes of surface intervals. For shallower dives – use double time of your bottom time. And it is recommended to not dive deeper than 60m more that once a day. Author of this essay was precisely following those rules during AIDA 4* course, and yet (most probably) was affected by fatigue and as a result had some minor DCS issues.
  2. Long bottom time. It causes more Nitrogen to absorb in tissues. So that consequent surface interval should be longer. A freediver should specially be aware of this doing FIM dives, because they feel like an easy dives. It is recommended to increase surface interval after those dives.
  3. Ascent rate. The quicker you go up the more probability of nitrogen to form bubbles, especially last 20 meters where pressure change is the most dramatic. That is why elite freedivers adapt a technic of slowing down the speed on the last 20 meters. [6]
  4. Depth. The bigger depth the more pressure that surrounding a freediver. That creates higher partial pressure in their lungs and makes nitrogen absorb more in tissues according to Henri’s law. Allow one PB a day for depth training.
  5. Packing. Increased amount of air in lungs allow to absorb more nitrogen for it to the tissues and increases the probability of DCS. Increase surface intervals.
  6. Dehydration.
  7. Fatigue.


  • Breathing pure oxygen on the depth 5-10m for 10 minutes can really help to avoid DCS symptoms even after freediver felt not well after the diving. Some Japaneese vilages that adopted that technique report more happier divers and less fatigue issues and DCS cases.
  • In some cases, it is recommended to do a full course of treatment in high pressure chambers.


What should a freediver do if he is expecting to cross the border of DCS safe freediving and is going (for some important reasons) do repetitive dive with short intervals. For example, AIDA Instructor course suggest 5 drills to 25m with one minute surface interval as a endurance test for future instructors.

(It is certainly highly not recommended to do so.) But what to do if he/she has to do that?

There are interesting studies [4] and [5], that suggest that aerobic training (like running for half an hour) 24 hours before the unhealthy freediving may help to reduce consequences of DCS-unsafe freediving.


In our research we showed that although the DCS risk is not the main risk discussed or perceived as dangerous it may affect a very important parts of freedivers body – brain and spinal cord. For competitive freedivers it is recommended to conduct brain MRI to track any abnormalities. For the general freediving public, it is better to stay safe and consider key DCS factors during their freediving session planning.


[1] –

[2] – Eric Fattah on DeepBlue –

[3] – DAN decompression sickness report –

[4] –

[5] –

[6] –

[7] – Good article/interview to read

[8] –

[9] – Hills BA, James PB. Microbubble damage to the blood-brain barrier: relevance to decompression sickness. Undersea Biomed Res 1991; 18:111-116.

[10] – Kohshi K, Wong RM, Abe H, Katoh T, Okudera T, Mano Y. Neurological manifestations in Japanese Ama divers. Undersea Hyperb Med 2005; 32:11-20.

[11] – DAN, BREATH-HOLD DIVING Workshop Proceeding, 2006