Author: Dr. Petar J. Denoble
The question about possible damages to the brain in breath-hold (BH) diving has been around for a long time. While the average people may hold their breath at rest (static apnea) for less than two minutes, trained BH divers easily double that time and elite BH divers can triple that to over six minutes. The top BH athletes regularly exceed 8 minutes and are close to ten. The world record in static apnea time without breathing oxygen in 2014 was set by Serbian Branko Petrovic at 11 minutes and 54 seconds. By now that record too has been exceeded. The superior performance of elite BH athletes could be attributed to their inherited biophysical characteristics, and some metabolic enhancement induced by training, but above all with the ability to postpone the break-through of apnea and sustain profound hypoxia. Inevitably, the longer the apnea lasts the worse hypoxia becomes, and it does affect the brain. The loss of motor control and consciousness during static BH competitions occurs at rates of 9.6% and 1.1% respectively. Negative acute effects of hypoxia on brain functions have been documented at high altitude in mountain climbers and in pilots. Studies of chronic effects of hypoxia in BH divers were less conclusive. Some previous psychometric studies did not find chronic effects that could be correlated to the years of practicing or to the number of negative neurological events. However, other studies using brain imaging and biochemical markers in elite BH divers have shown brain function abnormalities.
Recent study (1) involved 36 subjects divided in three groups: 12 Elite BH divers (EBHD), 12 novice BH divers (NBHD) and 12 participants without experience with BH diving (CTRL). The EBHD could perform static apnea longer 
than 6 minutes (mean BH time 371 seconds) and practiced BH for at least two years. The NBHD could perform apnea longer than 3 minutes (mean BH time 245 seconds) and practiced BH for at less 5 months and less than one year. All subjects were subjected to a battery of psychometric tests. The EBHD group showed statistically lower performance on most tests, especially on tests measuring the short-term memory. The decrease in function was correlated to the length of static apnea. It was characterized as a mild short-term memory impairment not amounting to a pathological score except in one case. The diver with the pathological score was the one with the longest static apnea (436 seconds) and the longest diving career (19 years). There was no difference in psychometric performance between NBHD and CTRL.
The paper provides a review of previous testing and findings and it appears that positive findings of this study reflect the longer static BH times of EBHD group in comparison to BH divers studied previously. It appears that extreme apnea comes at price as it would be expected.
The conclusion of this study is that elite divers who practice for years are at risk of short-term memory impairment.
References
- Billaut F, Gueit P, Faure S, Costalat G, Lemaître F. Do elite breath-hold divers suffer from mild short-term memory impairments? Appl Physiol Nutr Metab.2018 Mar;43(3):247-251. doi: 10.1139/apnm-2017-0245. Epub 2017
The Dive Lab 
I went through the study in details and I am quite skeptical about the approach.
First the conclusion are made based on one part of 7 test were indeed elite freediver have shown longer time to answer (16% on average).
For the remaining test elite freediver have shown similar results in general and even better resulst at binary task choices.
On top of that I am wondering why results are shown for 11 elite freedivers instead of twelve mentioned in the study. Within this sample of 11 elite divers one is clearly diagnosed with a pathologic score and still considered in the model.
I also believe that the figure 1 and 2 of the study are misleading to be fair the regression should have been done with the total sample of Novice and Elite to see real impact of years of experience. By making sample based on the outcome we want to obtain we are right into confirmation Biais.
Given the information on the table recording response time for the card 3 (average and standard deviation) I have recreated a normal distribution of the 22 freedivers that gives me below formula:
Time= 1.77 X years of practice + 85.95047 with a p value below 0.05.
So yes apparently years impact response time. But to make sure it’s the case we need to see the study the correlation between age and time of response for the non freedivers and analyze subsequently the significance of practice solely.
Dear Jean,
Your comments help to frame properly this study. The sample is relatively small and the analysis could have been done as you suggest. However, the number of available subjects for this kind of study is small and every bit of research done matters. I wanted to bring to attention of readers this paper. I could have been more critical about it, but this is one of rare papers that provides some evidence that there may be some long-term damage in extreme free divers. For the sake of free divers, I hope that there will be more studies addressing this issue and that we will get clear and unbiased answers. Thank you once more for opening the discussion. I hope more people will contribute.
Best regards,
Petar
Petar J. Denoble
Vice President Mission
Divers Alert Network