A recent article published by Dan Europe and still viewable on their FB page, I consider to be one of the most valuable pieces of research into an aspect of deep freedive physiology that I have come across in a long time.
It concerned genetic markers for a susceptibility to lung squeeze.
It brought to mind the vital importance  of knowing how to train for depth and the necessity of understanding of the role of NO in deep diving so here are some thoughts on the subject –

One of the principle markers discussed in the article concerned the performance and behavior of Nitric Oxide (NO) which is one of the main instigators of blood shift. NO is a vasodilator and also behaves like a very powerfull anti-oxidant. Blood shift (ischemia and reperfusion) produces a large amount of free radicals, that in deep diving threaten to overwhelm the system, and the first line of defense is NO. NO is produced in the paranasal sinuses and we have only a limited quantity.
The free radicals are largely responsible for feelings of exhaustion after a single very deep dive 100+ mts. The effort expended on a deep dive seems insignificant in comparison, say to a marathon. But the feeling and demands on the system are not that far apart, the reason – free radicals produced by blood shift.
I have been observing this phenomena for decades. The exhaustion does not come only from lactic acid but largely from ROS. It takes time for NO levels to return to normal after a deep dive, doing consecutive days of deep diving you risk incomplete Blood Shift and consequently a lung squeeze. What you need is not more training, it is REST, to let the NO return to normal levels. This lesson should have been learned after Nick’s tragic accident in VB.
This exhaustion produces all the symptoms of over training. The lesson More is NOT Better, has to be absorbed. It is  complicated by feeling the effort expended in a dive was not that great.
In blood shift the capillaries on the surface of the alveoli dilate more than 200%, and take up space that has been produced by the collapsing Alveoli (see experiments by Dr. Paul Gabbott, done on MT and Aharon Solomons in the Welcome Foundation of Oxford university in 1998). If this engorgement of the Capillaries is incomplete the result is lung squeeze.
Conclusions For PRE _ Training for Depth

1. Rest is vital for training deep dives – depending on depth, perhaps no more than 2 or max 3 dives per week, and for dives over 110 mts not more than one.

2. I have recommended weeks of preparation for depth using dives on Residual Volume. This allows one to safely train –

  • The blood shift, so that is comes on strongly and at once.
  • Deep equalisaton techniques, one can do several dives without risk of DCS as the time of each dive is short (20 mts a very deep RV dive takes  no more than 50 secs.
  • It allows one to train on RV, Separately, EQ techniques beginning with mouth fill and other dives beginning with no air in the cheeks to simulate the last part of a deep dive.
  • It does away with pressure triggers (where one stops each time at the same depth without explanation).
  • It acclimatizes the body to pressure.
  • RV dives give one a more accurate comparison to full lung dives it is easier to work out mathematically where you are at ,in your training.
 3. RV dives have to be done in the presence of someone who understands the special precautions necessary  and how to get maximum advantage from them.
FRC dives often considered safer for training as being less extreme are in fact far more dangerous, being less extreme the blood shift happens later with the risk of the collapse of the alveoli exceeding the dilation of the capillaries and producing a lung squeeze.
FRC diving has given exhale diving a bad name, in RV diving on the other hand you will be stopped by not being able to equalise long before you squeeze.
After this stage of training we proceed to tables of head down drops to introduce real time into the dive, we gradually reduce the weight in the hand and add it to the body of the diver.
In conclusion even if you are not genetically privileged and have some of the wrong markers, it does not neccessairly exclude you from deep diving, but you are advised to take very seriously the above recommendations and when training full lungs only increase the depth by not more than 1 mt per session and only if you can equalise on the bottom. Any blood in the saliva after a dive is not normal and should be taken very seriously.

Please comment for any questions.

Thanks for reading and watching.

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