A few questions... (Breathing Up Technique and diving environment)

[trux]

I don't think that's very relevant for a beginner, Trux. Has it ever happened to a freediver? There are guys diving 100m+ with minimal hyperventilation and nobody has had a CO2 blackout, at least that I'm aware of. Wouldn't you have to be experiencing extreme narcosis before you blacked out?

You are right, but it is my obligation to mention the possibility, whatever remote it is. Normal freedivers hyperventilate anyway, even if they think they don't, but if there is suddenly a newbie reading this thread, he could come to the conclusion that if he increases his CO2 level far over the average, he'd be perfectly safe from BO. I cannot claim such thing here.

And I do not think that the depth induced narcosis is necessary prior the CO2 BO. CO2 amplifies the N2 narcotic effects, but besides it, it has also toxic effects that are independent. At high CO2 levels you will black out even at atmospheric pressure.

 

[toku58]

Toku. I remember watching Davide Carrera prepare for a successful (and the easiest I have ever seen) 99M dive in constant weight. After getting in the water he lay face down and breathed through his snorkel for a couple of minutes. I was 1m away and could not hear his breathing. I now teach that to my students: if you can hear or see your buddy breathing before a dive, he is probably hyperventilating.

O.K. so I should focus on relaxing and just before decent, should I fully exhale all the air in my lungs and take a deep breath, then go down? Or is that still hyperventilating?

So I should not purge at all?

So far if I just do that I can only hold my breath (Static) for about 1 min.

If I purge a few times, I can hold for about 2 min.

 

[azapa]

So I should focus on relaxing and just before decent, should I fully exhale all the air in my lungs and take a deep breath, then go down? Or is that still hyperventilating?

Just relax and really float on the water, let the water take your full weight, nothing should be tense, check your breathing once in a while, it should be slow and relaxed, just moving your diaphragm in and out (like an half an inch max). You should feel no hunger for air, nor should you feel lightheaded. When your are ready (leave at least 3x your past dives time as rest) breath out slowly and fully inhale, starting from your diaphragm upwards. Then dive. This is not hyperventiation.

I should add that a good duck dive, beening correctly weighted, a good fining technique etc will do 2x more for your dive times than hyperventilation ever could, so approach more from that angle than the cheap trick angle


So I should not purge at all? No, it only helps the short term feel good factor but is dangerous and in the long run will not improve your dives

So far if I just do that I can only hold my breath (Static) for about 1 min.

If I purge a few times, I can hold for about 2 min.
So, keep practising until you can do 2 mins without purges too!


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[Kars]

For diving I found that the stress you may have at the surface can not be overcome on the way down.

So make sure you exhale just as slow as the other relaxing breaths, and inhale 'full' just as slowly as the other breaths. If the in hale takes too long, you can interrupt with a micro hold and breath in on top of the previous inhale. - Dave's double breath technique. But whatever you do make sure it's gentle and retains your relaxation.

Like Azapa said there are a lot of factors involved, and having a weak spot in one of them usually yields stress that reduces comfort, dive time and quality of the experience.
About training and advanced techniques. I think that for the different level freedivers there are different training techniques than can be used. Beginners should not try the empty lung stuff, for they lack the skill to read the subtle signals in relation to the freediving dangers involved with such types of dives. - for instance: BO comes VERY sudden with empty lung dives.
Take your time and practice to get to know your body and mind, there is so much to discover and learn, and it's a great ride!

Love, Courage and Water,

Kars

 

[toku58]

Thanks guys I'll work on it!

 

[JenR]

Okay, I have read this thread and I still have a question!
I am very new to freediving and after reading this, I know I am doing my breath-up wrong. I always take very deep breaths and deep exhales for at least a minute before I go under, which is obviously hyperventilating (I even feel high sometimes). I now know this is quite dangerous. I could do 3min static with HV.
How should I do the breath-up then? I haven't really read a clear description. I tried breathing normally (like you do always), whilst being very aware of my breathing, and then take 2 deep breaths and deep exhales before I hold it. In this way, I can only reach 2minutes! Is this the right way to do it?

 

[Kars]

Hi JenR,

The 'trick' is not reducing the CO2, but becoming more relaxed. Through this relaxation you'll produce much less CO2, that in turn will give you a smoother ride and longer breath hold.

I suspect that with hyperventilation your urge to breath comes at about 1'30 and quickly ramps up until you need to come up at 3'. With normal breaths I suspect you will feel the urge to breath to start at 45" - 1' then you go into the fight-mode and tens up and fight the contractions.

What you need is diaphragm flexibility together with better body and mind relaxation.

What I advice is to practice table A and B. What you can do is do a Table A (CO2) and 10 minutes after that a near maximum dive. Make sure you're hydrated and have an empty belly.

Relax take your time to improve your technique, focus softly on relaxation, not on time!

 

[neurodoc]

This turned out to be a very fascinating thread. I would like to add a thought to see what the group has to say about it, since not as much was discussed about it. The subject is the "passive" vasoconstriction and blood shift. To define that, I would say "active" VC and shift results from constriction of blood vessels, restricting and redirecting blood flow. Passive would result from pressure changes outside the blood vessels, either whole-body or chest pressure. Here is an example: If you dive down more than a few feet, the external water pressure may provide compression of the capillary beds in the extremities, raising resistance and reducing flow. A little deeper, and the veins and arteries in the arms and legs will get constricted from the compression forces. This may have the same effect as active vasoconstriction; a shunting of blood flow to the core. If we consider the difference between FRC and full-lung dives or breath holds, there is a big difference in chest pressure. If we raise the pressure in the chest cavity with full lungs, it would likely shunt blood away from the pulmonary circulation (right heart chambers) and into the main circulation. This would be somewhat counter to what we would like, I would think, and would seem to reduce the dive response. On the other hand, FRC, when under external pressure, is going to cause a relatively lower chest pressure which when combined with external water-pressure compression would likely cause shunting of the blood flow into the chest/heart and away from periphery much more than full-lung diving. So, this would seem to be a potential mechanism for the observation that FRC dives seem to create more dive response than full-lung dives, yet changes in blood gases do not explain this observation. It should mean that FRC dives result in more arm and leg lactate buildup due to reduced circulation compared to full-lung dives.
Any thoughts? it seemed logical in my mind, I hope it seems logical to some of you with far more knowledge and experience than I have
Richard

 

[Kars]

What you say seems logical to me too Neurodoc. Have you got any ideas how to test this?
Tomorrow is another pool session and I like to do an empty lung dive again. This time without slow burning food in my belly... Hopefully it's not too busy in the pool for a max dive.

 

[MUniRulez]

@neurodoc: imho there will be no constriction due to the external pressure. This due to blood being a liquid, and therefor hardly compressible. indeed the entire body is 80% h2o, so basicly only some cavities filled with air will be susceptible to compression. these would be obviously lungs, sinuses and other bone cavities, and possibly gas buildup in the intestines.

cheers, Francois

 

[neurodoc]

Francois, what you said makes sense in concept-you are right and fluids are not compressible. But, the volume taken up by blood inside the blood vessels is a variable; compression from external forces does in fact reduce the blood flow. That is why a sphygmomanometer (blood pressure cuff) works-you are restricting the blood flow by applying an external pressure to the limb. The blood going into a limb via blood vessels must overcome whatever pressure exists outside the body in order to keep the blood vessel open. So, when you consider the variables the human body presents, the blood is not compressible but the blood vessels are, since the volume of blood flowing through them is not static but is variable and the walls of the vessels are elastic.
Richard

 

[trux]

In fact François would be right if the body was completely filled with fluids - the blood vessels would not constrict due to the external pressure, regardless if they are compressible or not. Of course, the constrictor muscles can restrict the blood flow, but a homogeneous external pressure would definitely not do it if there were no compressible space in the body, which is not the case (we have lungs and other cavities). The blood-shift is the result of two independent effects - the hydrostatic environmental pressure together with negative intrathoracic pressure gradient, and the peripheral muscular vasoconstriction. If you'd fill the lungs (and other cavities) with a liquid, the muscular vasoconstriction would still work for reducing the blood flow, but the external pressure would not affect it.

 

[MUniRulez]

This negative intrathoracic pressure gradient would be the result of peripheral vasoconstriction and intrathoracic vasodilatation I presume?

And I have heard some reports that actually plasma backfills sinuses and alveolae at depth due to the pressure.
Shifting back to the vessels when pressure decreases.

 

[neurodoc]

Trux, that does make sense. Thank you for your reply. If we were completely filled with fluid, and if the blood vessels were all of equal diameter and elasticity then there would be no blood shift. I have a feeling that blood would preferentially be squeezed out of the capillary beds and into the larger blood vessels when the whole system is compressed, due to fact that larger the vessel the greater its cross-sectional area in a non-linear fashion. Cross-sectional area will increase by a square of the radius, so the bigger vessels always have more capacity to absorb volume changes and the smaller ones are more prone to lose their volume under pressure. I'm not totally sure about this but it seems intuitively reasonable. I like your explanation of the pressure gradient due to intrathoracic space. It is what I was implying when comparing full-lung dives with partial lung or FRC dives-perhaps the full-lung dives cause more pressure in the thoracic cavity, which gives the blood from the extremities less of a negative pressure gradient, so more stays in the extremities. If diving with less air in lungs, less pressure in thoracic cavity should allow the external water pressure to drive the blood from the extremities into the thoracic cavity, causing a pressure-induced peripheral vasoconstriction. Also, any peripheral vessel constriction would have more of an effect if there is more pressure gradient.
I wonder what kind of study it would take to see how much of the peripheral loss of circulation is due to pressure gradient and how much due to blood vessel wall muscular contraction....

 

[trux]

The elasticity and the diameter would not result in constriction as long as there is no air at all in the body. Fish would have problems with peripheral blood flow in such case. What can have impact is the hydrostatic pressure difference between the bottom and the top part of the immerged body. Especially near the surface where the pressure gradient grows rapidly with depth.

 

[trux]

This negative intrathoracic pressure gradient would be the result of peripheral vasoconstriction and intrathoracic vasodilatation I presume?

No, it is not the result. It is the cause.

And I have heard some reports that actually plasma backfills sinuses and alveolae at depth due to the pressure.
Shifting back to the vessels when pressure decreases.

Not really. Have a look at this thread for the explanation: http://forums.deeperblue.com/freedi...ng-water-accumulation-breath-hold-diving.html

 

[MUniRulez]

So what causes the pressure difference?

cheers, Francois

 

[trux]

So what causes the pressure difference

The ambient pressure of the water column compresses the body and hence also (better told especially) the lungs, but due to the limited flexibility and elasticity of the chest and diaphragm, with the growing ambient pressure the difference between the ambient (external) pressure of water, and the pressure in the lungs grows. This transpulmonary gradient then contributes to the blood shift from extremities to the pulmonary vessels, which reduces the inner volume of the lungs, and compensates the pressure difference (but certain negative gradient remains anyway).

 

[MUniRulez]

...This transpulmonary gradient then contributes to the blood shift from extremities to the pulmonary vessels...

thx trux!

Being submerged actually helps us survive being submerged! Who would have thought ;-)

cheers, Francois

 

[neurodoc]

So then, the water pressure is in fact part of what causes blood to shift from the extremities to the thoracic cavity. When we look at breathing-up technique, would a full lungful of air then cause relatively more pressure in the chest than a partial or FRC lungful? Would a full lungful of air reduce the blood shift since there would be less transpulmonary gradient? and therefore, FRC or partial fill would have more of a transpulmonary gradient and hence more blood shift? I'm still working on completely understanding the difference, because I've noticed (as Kars has apparently) that I can't go much farther with full lungs than partial, and it is less comfortable as well. Trux and other contributors, thanks for sharing your knowledge and helping us learn! Being a chiropractic neurologist I understand physiology more than most, but am pretty new to freediving and finswimming so this really helps me to learn how things work underwater