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

[Johan Andersson]

Connor and Ivo, I will return and try to answer/comment your latest posts, but I will probably not do it in a few days. Just wanted to let you know that even if I will not post in a while, I have not left the thread. It's just that I will have very little computer time in the near future (busy teaching today and have other plans for the weekend)...

/Johan

 

[cdavis]

Kars: FRC learning curve? LONG but rewarding. There is actually a pretty good history of my progress in "Exhale diving for the average diver"

Its been very interesting to watch progression. I'm pretty sure that much of what you have to learn to do FRC, slow down, minimal breathup, relaxation, etc, is a big help in full lung diving too. Where exactly the optimal point of lung "fullness" is is hard to see and is probably a moving target. One thing I have seen, inhaling substantially less cuts your dive time and depth initially. Training very quickly restores time. Much more slowly, training and practice result in longer dives than full lung and eventually most if not all of your depth ability comes back. I was completely stunned to do 109 ft last fall on FRC.

Johan, take your time and thanks again. We have some thinking to do.

Connor

 

[Johan Andersson]

Connor, for answers regarding FRC diving I guess science is just following you and the others doing it. There is no scientific studies on this topic (as far as I know). It is difficult to perform these studies as there are so few divers performing this type of diving (at least at a convenient distance from a suitable lab doing apnea research).

So 60 per cent might be the magic number.

However, the difference between the diving responses initiated at 60% and 85/100% were small (in conditions resembling static apnea). I don't think it could be the only factor explaining your experiences. At least, I will be surprised if that eventually turns out to be the only or major factor.

I find it difficult to understand this from a gas exchange/gas storage point of view. The following calculation is a major simplification, but I think it illustrates what I want to say (values are to some extent based on observations/measurements). Lets say you have a diver with a TLC of 10 liters (RV 2 L + VC 8 L). Diving at full lungs (assume 15% O2 in lung gas) gives you a total lung O2 store of 1.5 liters. Add a blood O2 store of 0.9 liters for a total of 2.4 liters of O2 in lungs and blood.

Now assume the same diver inhaling 60% of VC, that is 6.8 liters in total (RV 2 L + 60%VC 4.8 L), with 15% O2 in the lung gas. This gives you a lung O2 store of 1.02 liters. Add the blood O2 store, 0.9 liters, for a total of 1.92 liters of O2 in lungs and blood.

So, with 100% VC you have 2.4 L of O2 and with 60% of VC you have 1.92 L of O2 (a 0.48 L difference). Not all is usable, but lets ignore that for the sake of making the argument easier.

Finally, assume you have an O2 consumption of 0.25 L/min (a low O2 consumption; I have not recorded a lower average than 0.28 L/min in my studies). This is with a diving response initiated. The time that the O2 stores can support aerobic metabolism in the two cases above is 9.6 min (100% VC) and 7.7 min (60% VC), nearly a 2 min difference. Connor, you say you can dive longer at FRC that with full lungs. I can't explain that.

To get the same time from 60% VC as with 100% VC, the O2 consumption would have to be reduced to 0.2 L/min at 60% VC. The lowest value I ever saw during apnea is 0.21 L/min, if I remember it correctly. Maybe a further reduction is possible, but to explain longer times at FRC than full lungs, I guess you need something else as well.

Of course, such things as buoyancy, relaxation, etc, may be involved.

FRC theory says taking down more co2 helps the dive reflex, especially vasoconstriction

But at the same time, FRC diving will also cause hypoxia faster, and hypoxia definately augments the diving response. So, how can you/we say if it is hypercapnia or hypoxia that is the factor at play here? (Hypoxia will not be a factor in deep diving, with the increase in PO2 at depth, but possibly in dynamic or static.)

Discussing this makes me realize that this probably requires some more studies. Your experiences (that hypercapnia augments the diving response) are not in line with the previous scientific studies I based my arguments on. Of course, I'm also curious to find out why that is so. I'll try to do a study on this.

On your previous question about why assume people with differing co2 trigger levels might respond differently to mild hyperventilation, I'm not really assuming anything. Its just my observation that some people are much more susceptible to B0 than others and I'd like to know why.

This characteristic (susceptibility to low O2) probably follows a normal distribution, just as most physiological variables, and there are many contributing factors.

/Johan

 

[Mullins]

Connor, you say you can dive longer at FRC that with full lungs. I can't explain that.

Are we talking hypoxic limits though, or just comfort levels? FRC does feel pretty good because of the free ride down and low buoyancy change.

 

[Johan Andersson]

It is a pity the documents are not available publicly in full text. I'd love to see the details, and the quantitative results.

PM me your e-mail address and I'll send them to you.

It is also a pity the studies are not more complete: At the first one, I miss a measurement at hypercapnia.

In their second test, there was hypercapnia during the apnea (normal refers to during the breathing before apnea). Test 2 (with hypercapnia developing) did not elicit a more pronounced vasoconstriction than test 3 (hypocapnia).

And at the second study, if I understand it correctly, they actually did not measure values at a breath hold (except of the first control group BH1), but all four groups BH2-BH5 were rebreathing.

Yes, that is a "drawback". But even with this, when I look at their results I draw the same conclusion as the authors; "The total peripheral resistance (vasoconstriction) during BH with reduced alveolar CO2 levels increased more than during BH with increased CO2 levels from the pre-BH levels." As I wrote in the answer to Connor, I believe this deserves further studies, because this discussion has made me curious to understand why these studies are not in line with your experiences.

BTW, did they compensate in their measurements of the peripheral resistance for changes in cardiac output?...Or is the type of measurement they did already independent on the cardiac output?

The study you mention has no relevance for what we are discussing. Cardiac output is "compensated" for. The calculation of total peripheral resistance (related to preipheral vasoconstriction) is based on measurements of cardiac output and blood pressure. I could explain in detail if you want to, but that would take us even more off topic (as if this thread has not already "taken left where we should have taken right" ).

To add some more thoughts, there are more than the studies I cited above that shows that hypercapnia per se does not cause peripheral vasoconstriction (however in conditions other than apnea). For instance, see this study (full text available to everyone):
Differential responses to CO2 and sympathetic stim... [J Physiol. 2005] - PubMed result
It is also known that CO2 is a vasodilator when it acts locally at the peripheral arterioles. However, this effect is not as pronounced as in the cerebral vasculature.

/Johan

 

[Johan Andersson]

Are we talking hypoxic limits though, or just comfort levels? FRC does feel pretty good because of the free ride down and low buoyancy change.

Yes, that are of course things to consider.

/Johan

 

[cdavis]

Mullins has a point, at least for me. Lousy c02 tolerance and poor will power mean I come up well before some other divers , even when I'm trying to push it during practice. I've never gotten to a state of substantial hypoxia. Also, I'm serial diving. Comfort is the name of the game. FRC diving definitely makes me comfortable, longer. That is almost certainly a combination of the technique changes needed for FRC and the effects of exhale.

Johan, some experiments on FRC subjects is definitely in order. You and me are not the only ones who don't understand the physiology of what is going on. The available science and FRC experience don't seem to match.

Some thoughts: the example (10 L lungs) is sensitive to lung size. Drop the lung size to 7.4, 5.8 vc + 1.5 l rv(close to me) and the apparent advantage of full lung drops considerably. A couple of other things might be operating. Cumulative blood shift is encouraged by FRC. The amt of blood pooling in the lungs(between dives) is considerable, a liter maybe? At least half of that is fully oxygenated, increasing the blood supply 02 contribution. Blood pooling in other organs may also carry a higher 02 level than normal flow. It feels to me like general relaxation is much greater with FRC. This has to affect 02 consumption. Finally, the whole way you approach diving and your body reacts to it is different with FRC. Hard to explain, but obvious to those of us doing it. I suspect that much of this reduces 02 consumption and c02 production.

Question. I'd always assumed(could easily be wrong) that RV air was not 02 useful. The example counts it as the same as VC air. Is this reasonable?

Thanks

Connor

 

[Johan Andersson]

Question. I'd always assumed(could easily be wrong) that RV air was not 02 useful. The example counts it as the same as VC air. Is this reasonable?

Here, it doesn't really matter if the oxygen is in the RV or VC at the beginning of apnea. It is the composition of the alveolar gas at the end of apnea that matters.

But it should be noted that the illustration/example was simplifying things (as I wrote). You can't use all the O2 in your lungs. At an alveolar PO2 below approximately 20 mmHg you will probably BO. You can't go to 0% in your lungs.
(See for instance Alveolar gas composition before and after maximal ... [Undersea Hyperb Med. 2006 Nov-Dec] - PubMed result)

The same goes for the blood O2, you can't use it all. The saturation of arterial blood will be around maybe 35-40% at BO, and venous saturation around 25-30%. There will still be some oxygen left in your body's stores at BO. That was ignored in the example.

/Johan

 

[miguel-van]

This is some serious info on the beginner forum

 

[Kars]

I do full lung, FRC and empty lung diving.

As Johan may recall (I took part in his study in Sweden some years ago) I'm a skinny tall guy.

In search of understanding my body I've done experiments.

I can swim to samba in dynamic, but when surfacing I hardly feel any lactic. My Dynamic distance has been limited to just 134m for years because of this limit.

When I swim empty empty lungs something amazing happens, my limps do acid up while swimming. AND contrary to full lungs my mind remains crystal clear, instead of the fogging up that happens during full lung diving.

Some other facts, I can do a reasonable static, pb 7', poor dynamics, better at depth.

So I'm trying to understand what's happening and one day, about 4 months ago, I get the idea that the O2 bandwidth between my muscles and bloodstream may be the difference. You see I can perform doing long distance stuff, meaning my body is good in maintaining a high gas exchange / bloodflow with my muscles delivering O2, taking CO2.
This means that relatively my body goes late into anaerobic mode.

To try this I went to a stretch of land where I do my apnea jogs. Former pb was 180m.
This time, full lungs like normal, slow lazy start, just a tat under normal, jogging until first contraction, than -new- step on the gas going at 90% speed. By increasing the muscle demand over that what my system can exchange (bandwidth) I force it to operate in anaerobic mode, hence leaving the remaining O2 in my system for my brain and hart to use. After a huge pb of now 260m, I noticed my limbs were lactic, while my brain was still surprisingly clear at the end of the road.

Since this I tried it in the pool, swimming the first 50m slow, and the remainder stepping on the gas so to speak, and it resulted in a pb as well, 150m.

Johan have you got any idea what's happening? Does the mechanical model I now have make sense?

In regard to the FRC diving, I think having a normal level of CO2 in the bloodstream does help to safe O2, because the body does want to have the CO2 at a specific level and will adjust the metabolism to restore to normal CO2 levels, burning O2.
Now when one starts a dive with low CO2, the body goes into burning extra O2 to restore the CO2 level. When the CO2 normal level is reached, I suspect that the O2 consumption goes down, but starting from a higher vantage point the body will keep using more O2 than a diver that started out with a normal CO2 values.

Does this make sense?

 

[Johan Andersson]

Johan have you got any idea what's happening? Does the mechanical model I now have make sense?

In regard to the FRC diving, I think having a normal level of CO2 in the bloodstream does help to safe O2, because the body does want to have the CO2 at a specific level and will adjust the metabolism to restore to normal CO2 levels, burning O2.
Now when one starts a dive with low CO2, the body goes into burning extra O2 to restore the CO2 level. When the CO2 normal level is reached, I suspect that the O2 consumption goes down, but starting from a higher vantage point the body will keep using more O2 than a diver that started out with a normal CO2 values.

Does this make sense?

Kars, of course I remember you from Nordic Deep. Unfortunately, I don't know if I have any good physiological explanations for your experiences.

Where did you get the idea about low CO2 levels leading to increased metabolism? I'm not aware of a direct connection between blood CO2 levels and metabolism. The body has solved the problem with fast (acute) reductions in CO2 levels in a much simpler way. A mechanism which all breath-hold divers is (or at least should be) aware of:

If you are low on CO2 (for instance following hyperventilation), the body does not compensate by increasing the metabolic rate but by a reduction in the urge to breathe/ventilation. If breathing continues, you simply hypoventilate after a period of hyperventilation. This leads to a retention of CO2 and normalisation of blood CO2 levels (without any change in metabolism). Of course, that's why most people immediately feels that it will be easier to breath-hold after hyperventilation.

/Johan

 

[azapa]

.....

I can swim to samba in dynamic, but when surfacing I hardly feel any lactic. My Dynamic distance has been limited to just 134m for years because of this limit.

When I swim empty empty lungs something amazing happens, my limps do acid up while swimming. AND contrary to full lungs my mind remains crystal clear, instead of the fogging up that happens during full lung diving.

Some other facts, I can do a reasonable static, pb 7', poor dynamics, better at depth.

warning: hijack to an already hijacked thread

Kars, I too have been trying to figure out what type of diver I am and you sum it up pretty well above: I too can swim to samba very easily, but have never had lactic at all, even less to the point I can't swim. I also have a decent static and am good at depth (better said, I have very comfortable bottom-times spearing).

How are you at aerobic sports? I have realized that I am terrible at them and getting worse the more I train apnea.

 

[Kars]

Thanks Johan,

Simple question, have you seen, or do you know of higher O2 consumption levels (doing the same amount of work) when the subject has a lower than normal CO2?

The other question on the gas exchange bandwith between muscle and bloodstream, has this been researched? - I suspect long distance people are have a higher bandwidth than sprint or powerlifting types.

Apaza, yes I'm am above average in aerobic sports. Without any specific training I surprise my running friend keeping up and sustaining a decent pace.
Are you good in weightlifting sort of explosive sprint type of sports?

 

[azapa]

Apaza, yes I'm am above average in aerobic sports. Without any specific training I surprise my running friend keeping up and sustaining a decent pace.
Are you good in weightlifting sort of explosive sprint type of sports?

Kars, my point was I am now completely crap at aerobic sport. No weight lifting. For example bodyboarding last week, the paddle-out in an easy day (1.5 to 2m surf) almost killed me. I can cycle OK (strong legs) and am a good snowboarder. But put me in a basketball court, or ask me to run fastish and I want to vomit with exhaustion in 20 mins... Of course, I could just be getting old ,,,:crutch

 

[cdavis]

Johan,

Kar's results do seem wierd, but most, if not all, divers who dive FRC extensively report various versions of the same things. It appears that extensive FRC diving brings on physiological changes that enhance our diving. It certainly feels like the body is slowing its metabolism in response to FRC and the more we do it, the more it slows down. Further, breathing less during breathup improves performance. We have developed a set of "reasons" to try and explain what is happening to us. They might be wrong as heck, but the results are hard to argue with.

Some research is definitely in order.

Connor

 

[Kars]

To give some weird numbers. My VC is 5.05L, I weigh 74 Kg, 189cm tall, skinny body type.
Inhale + packing DNF pb: 111m
forced exhale + 40s static + DNF pb: 62m - easy dive expected to grow.

I guess there is a lot to research, but I must say the seal approach seems to yield to cool helpful secrets.

 

[toku58]

Wow! All this info, is just too much for me to grasp as a beginner.:blackeye

Could you guys just simplify this for me?

What, or how should I practice to improve my working time. (Reef spearfishing) What is the correct way to breath up?
Should I do, Normal breathing with 3-5 purge breaths before I go down? I want to avoid SB.
So I take it that hyperventilation to the point of lightheadedness is a really bad thing?
Sorry if this is a noob question. I'm really new to this, but I'm trying to be as prepared as possible before I attemp to spearfish.

Thanks in advance!:friday

 

[trux]

Well, it is relatively simple - roughly told the less you hyperventilate, the safer you are from BO. But in the same time the dives may be less comfortable. 3-5 purges is already an important amount of hyperventilation, so I do not think it is wise.

On the other hand be carefull not to dive with a too high CO2, and to important depth in plus - due to the high PaCO2, the toxic effects of CO2 could cause a blackout too, and it could be even more dangerous than a hypoxic blackout.

I usually advise to stop focusing on breathing, or trying to control the breath-up; skipping purges, etc; and instead of it focusing on the rest and relaxation. Your body knows better than you how much you need to ventilate. Just under stress, it may start hyperventilating too - that's why calming down is important.

 

[azapa]

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.

 

[Mullins]

On the other hand be carefull not to dive with a too high CO2, and to important depth in plus - due to the high PaCO2, the toxic effects of CO2 could cause a blackout too, and it could be even more dangerous than a hypoxic blackout.

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?