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The actual impact of Low CO2

Nathan Vinski

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Something that a few recent discussions, both on DB and in person, have lead me to question a lot of what we claim about the dangers and risks surrounding hyperventilation.

So yes, I agree with the science around the Bohr effect, that high levels CO2 can improve dive response, and that hyperventilation is potentially very very dangerous as it, especially with beginner untrained freedivers, lead to blackouts without any warning what so ever.

As an Instructor I am a firm believer that you should never ever hyperventilate before a dive, but as an athlete I am not at all convinced.

This all started with a very interesting dry static experience 2 years ago. One day I was listening to wim hoff on the joe rogan experience podcast while he talked about his method for healing through breathing & breath holding I decided to dive it a try and on hold #3 I managed, after breathing until I couldn't feel my face arms, and feet, 4:37 FRC dry (mostly static). My HR started at 75 beats/min (30 beats faster than resting) but at 2 minutes my rate was 32. This dropped further to 30 measured from 3:30 -4:00. At 4:00 I ran up 2 floors from the basement to the 2nd floor bathroom so I could see the colour of my lips. I stopped with pink lips at first contraction, did 2 recovery breaths and made lunch thinking "that was interesting". The next day I tried a normal ventilated FRC static aiming for 5:00. Starting HR 40. At 2:00 my HR was 43, and at 3:48 I had a small LMC. Then depth training started and I kinda forgot about the whole thing as I was afraid to over breath.

~2 Years later (7 weeks ago) I was doing some packed 4:00 statics for stretching and I got hold of a mediocre pulse-oxi. Similar experience.. With normal breathup 4:00 ended with around 60 beats/min, and around 85% O2. Extreme hyperventilation 4:00 ended with 50 beats/min and around 95% O2.

In both cases evidence suggests that my dive response is better over the breath hold with hyperventilation, despite a much higher starting HR. This also seemed to greatly reduce O2 consumption or if you look into it, Improve O2 storage.

Could increasing the Bohr effect actually help us? Theoretically we cannot increase Arterial blood O2 but what about the veins. "sticky" alkaline blood might help us oxygenate the veins. As time goes on and we build up CO2 though the breath hold eventually we reach normal acidity levels allowing us to use the extra oxygen.

Is it possible that CO2 is not the main/only trigger for dive response. On dry breathholds with no other stimulus for DR common freediver knowledge suggests that CO2 is the only thing that will tell our body to save O2. This, at least in my case, seems to be false as my biggest drops in HR and lowest ending HR come with extremely low levels of CO2. What else triggers the "dive response" bradycardia mainly? could high alkalinity play a roll more significant (maybe for different reasons) than high acidity does.

I have similar experiences with deep (55m bi-fins) dives. My most difficult dives in terms of recovery are (normal CO2, normal neutral buoyancy (1/3 target depth), normal freefall (1/2 target depth). My best results in terms of recovery are (very low CO2, deep neutral buoyancy (1/2 target), and no freefall). My thoughts are that I store extra O2 in the veins, and due to not freefalling I can build up back to normal levels of CO2 to use the extra oxygen for the end of my dive (stop bohr effect and limit shallow water BO). I would like to do the comparisons with HR, dive time, and O2 levels as up until now I've been basing this all on feeling.

most of my tests however have been 3:00+ dives to 20m which also seem to be much better with less CO2, not in terms of urge to breath but in terms of the colour of my lips and number of possible reps. With normal CO2 2x is my maximum before performance starts falling off, with very Low CO2 I can do 3-4 reps.

I would be very interested in hearing some thoughts on this and maybe some ideas on how to test what's going on a little more scientifically.

Please, before anyone yells at me for being "unsafe", I dive around 5 times per week ( I know my sensations), with the same 3-4 dive buddies who are all aware of exactly what I'm doing and who know my diving very well. I make only very small changes at a time to limit unknown variables. And Finally, even with face numbing low levels of CO2, at around 2:45 dive time on the slow 20m dives, I get the strong urge to breath so 3:30+ doesn't sneak up on me resulting in any BOs. A little FYI, I've never had even an LMC in depth and I haven't been any closer since I've tried any of this, I actually feel (buddy feedback supports) that I'm actually farther away from it.

Lastly and probably most importantly: Anyone reading this, who hasn't been diving as much as possible for 5 years, who doesn't have 5-7 days per week to make tiny adjustments over time, and doesn't have consistent buddies, do not start breathing like crazy hoping for good results. Potentially loosing the urge to breath is very dangerous, especially in depth and results are going to vary a lot, person to person. With any experimentation, start with dry holds and if you change anything in the water it should always be done as controlled as possible changing only 1 variable at a time.

Preferably let someone else do it (me) and when I eventually get around to properly testing these things I'll let ya know..
 

psimian

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I've been doing a lot of reading on capnography, and CO2 in general in my quest to come up with a freediving computer. As great as it would be to collect some hard data on CO2 levels, and their effects while freediving, it doesn't look promising.

When someone is put under anesthesia, the doctors monitor both respiratory CO2 (PetCO2), and arterial CO2 (PaCO2). All of the non-invasive techniques that I could find for measuring PaCO2 won't work with freediving because they are based on electrochemical phenomena, and can take several minutes to register a change. Modern PetCO2 monitors work much like pulse oximeters in that they measure how much infrared light is absorbed by a volume of gas. They're accurate, and the reading is instantaneous, but they only work if you're breathing (slight problem here!) Since CO2 levels vary wildly throughout the lung tissue depending on the amount of alveolar perfusion (blood supply), the only way to get an accurate picture of how much CO2 is in the lungs is to analyze an entire exhalation. It might be possible take pre/post dive PetCO2 readings, but I don't know how much use that will be without also knowing the PaCO2 because the one reading is not always predictive of the other (which is why hospitals monitor both).

It is possible to measure CO2 dissolved in water using IR absorption, but I have yet to find any optical PaCO2 meters (like the fingertip pulse-ox, but for CO2). I'm going to guess this means that this method doesn't work through tissue, or nobody has figured out how to filter the signal enough to make it useful.

To confound things further, your metabolism can have a huge effect on CO2 production. I've seen varying reports (mostly from studies on running), but metabolizing fat uses around 5% more O2, and produces 25% less CO2 per unit of energy than metabolizing carbohydrates. So, if you've been diving for an hour or two and your body enters a fasting state you might have dives that feel much better in terms of CO2 levels, but actually put you at higher risk of hypoxic blackout. The easy solution is to drink gatorade, eat goo packets, or anything else that ensures you've got enough carbs in your system the entire time you're diving.

The upshot of all of this is that I suspect the conflicting reports about the effectiveness of hyperventilation are partially due to not having a good way of capturing an accurate picture of CO2 levels throughout the body on a second-by-second basis. Add to that the subjective and highly variable individual experience of high/low CO2 levels, and we've got a real quandry.
 
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Lauri_A

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My current understanding of CO2/Hyperventilation in competitive freediving is summed about so, of course depends on the person but this is looking at several top level divers:

Dynamics - 3-4 deep breaths, any more and you don't get the Bohr effect enough and it starts eating your performance.

Static - Hyperventilate a lot but needs training, CO2 builds up so slowly that the body has time to adapt and you still get the Bohr effect etc. The extra relaxation that you get from hyperventilation easily compensates for the negative effects, if you can move your contractions by 1-2 minutes it's a massive help.

Depth - Have very little experience, there is the big plus side of delaying contractions a lot but the risks are not worth it personally. I haven't see anyone hyperventilating in competitive depth diving.

My opinion is that hyperventilation is always compensating for the lack of tolerance, it's a shortcut and even in static the best performance would likely be without any hyperventilation. But in competitive diving there's a place for it definitely, some persons can benefit more than others and there are no clear guidelines other than you need to test, adapt and experiment.

As in the other discussions, HR may not be the best indicator for O2 consumption, Bohr effect or cerebral vasoconstriction will probably not show in HR but will still lower the BO limit.

I've done all my max performances without any HV, have tried it but it results in a really short warning time in hypoxia before LMC/BO. Still I will keep testing it in static as there it has the most benefits with the smallest risks.

There is also a personal tolerance for HV, for me without any adaptation around 2:00 of hyperventilation is on the limit of blacking out.
 
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Nathan Vinski

Nathan Vinski

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Apr 19, 2015
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My current understanding of CO2/Hyperventilation in competitive freediving is summed about so, of course depends on the person but this is looking at several top level divers:

Dynamics - 3-4 deep breaths, any more and you don't get the Bohr effect enough and it starts eating your performance.

Static - Hyperventilate a lot but needs training, CO2 builds up so slowly that the body has time to adapt and you still get the Bohr effect etc. The extra relaxation that you get from hyperventilation easily compensates for the negative effects, if you can move your contractions by 1-2 minutes it's a massive help.

Depth - Have very little experience, there is the big plus side of delaying contractions a lot but the risks are not worth it personally. I haven't see anyone hyperventilating in competitive depth diving.

My opinion is that hyperventilation is always compensating for the lack of tolerance, it's a shortcut and even in static the best performance would likely be without any hyperventilation. But in competitive diving there's a place for it definitely, some persons can benefit more than others and there are no clear guidelines other than you need to test, adapt and experiment.

As in the other discussions, HR may not be the best indicator for O2 consumption, Bohr effect or cerebral vasoconstriction will probably not show in HR but will still lower the BO limit.

I've done all my max performances without any HV, have tried it but it results in a really short warning time in hypoxia before LMC/BO. Still I will keep testing it in static as there it has the most benefits with the smallest risks.

There is also a personal tolerance for HV, for me without any adaptation around 2:00 of hyperventilation is on the limit of blacking out.
All of those reasons are precisely what I'm looking at eventually testing properly. Again I'm not very convinced that any of that stuff really happens the way we think it does.

Bohr effect: alkaline blood holds on to oxygen. 1: this would increase vein blood O2 saturation by a huge amount. 2: Later on in a breath hold we will reach normal CO2 levels and our blood can once again release the O2.

Cerebral vasoconstriction: Low CO2 at the start limits brain O2 consumption, later in when CO2 level reaches normal our brains will get enough blood again. Same BO threshold with less initial consumption.

My best dynamics ( +95% hypoxic limit) were done with tingling fingers+lips after breathup.

And so far there's been no increase of risks in depth diving. My surfacing with Low CO2 feels much more lucid on near maximal dive times (20m dives) with a higher maximum +20 seconds of confident dive time. On 10m less than PB dives (still a physical effort but very easy easy), like I said much better recovery, more lucid, faster recovery and more possible reps. Normal CO2 i can do 55 x 2 and that's pushing it. Low CO2 I've done 3x55m. Same 15min surface intervals for both suggests I was much farther from the limit on each dive.

I also don't think, at this point for me, tolerance plays any role. I could (I don't) push dry static to LMC with any breathup with or without a warm up. My limits are O2 related, not CO2 related. This allowance me to easily test the O2 effects of different breathups.

I still agree that especially with beginners or less in-tune people the risks don't outweigh the rewards. It's much easier to teach BO with HV. I also think it's super individual, for example I still get Contractions with extrem HV, my buffering of CO2 must be naturally bad and it build up very quickly negating the possible negative effect of HV and allowing me to keep the positives. That's why I'm looking for ways to more scientifically test this.
 
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Lauri_A

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Interesting topic, good that you are experimenting with this. I think personal differences are massive in this so simple rules are hard to give. I try to keep competitive diving separate as in normal recreational diving hyperventilation shouldn't be relevant unless spearfishing or doing repetitive dives with short intervals.

Like said above, controlling your current CO2 level may be very difficult due to varying exercise levels, eating etc so I think most dives are done with a wide range of CO2 in the blood. I try to control my level before diving by bringing my breathing down to almost urge to breathe level so I know where I am on the CO2 scale, then keeping just above it.

I think the blood acificication (Bohr effect & cerebral vasoconstriction) is working a little different than you write. CO2 levels are not the same with / without HV meaning you reach much lower pH values without hyperventilation meaning that the extra high CO2 gives you more O2 through Bohr effect and better cerebral perfusion with higher vasodilation.

What I meant with tolerance is more about relaxation, not about psychological limits. I would say most people are not able to be as relaxed through contractions as without them as well as some small muscle work being done with diaphragm so there is likely higher O2 consumption when you feel unpleasant and get strong contractions. Strong hyperventilation gives quite strong feelings of pleasure and gives you maybe 1-2 minutes more without contractions meaning you can stay relaxed for a longer time leading to slower O2 consumption. My one trial with static was 1-2 minutes of giggling underwater in the start and in the end tapping fingers in rhythm on the pool edge at 5minutes - usually at 5 minutes I'm in sufferlandia, so the extra relaxation can be massive.

It's almost a zero sum game - you lose in the Bohr effect & cerebral vasoconstriction but gain in relaxation, it depends on the person how the scales are set up.

I think you can get adapted to anything, I have seen people hyperventilate so much that I would black out but they still perform in a very high level, much higher than without it.

If you're O2 limited, do you have other angles to approach than hyperventilation? Stronger dive reflex introduction, more hypoxic tolerance?
 

MarcinB

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Nathan, SpO2 values with and without hyperventilation are not 100% comparable. Lower CO2 level increases the affinity of Hb towards oxygen, so SpO2 will be higher at given pO2. Therefore, even if the amount of oxygen consumed is the same with and without hyperventilation, SpO2 will be higher after hyperventilation (it will happen at the expense of lung oxygen stores).

Hyperventilation changes many variables, Bohr effect and cerebral vascular conductance are of course important but there is much more than that. It also increases body oxygen stores (by 5-10%), induces peripheral venoconstriction, affects brain oxygen consumption and dive reflex. As far as DR is concerned, the effect of CO2 seems to be much weaker compared to face immersion or hypoxia. This aspect is not well studied, however, the conclusion from the available data is that hypercapnia may impair bradycardia but at the same time improve vasoconstriction.

From the general experience it seems that hyperventilation can substantially improve performance in static but its effect in dynamic is rather detrimental. In my opinion the greater is the effort during the dive the greater are benefits of hypercapnia. There are, however, exceptions. I know a very experienced high-level freediver who hyperventilates heavily before every dive, no matter if it's static, dynamic or deep diving. From his words, he wouldn't be able to achieve good results without hyperventilation.
 
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Nathan Vinski

Nathan Vinski

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I guess it's like I mentioned, very very individual.

Lauri, I did some reading on the Bohr effect. First off, I did understand the main concepts but did write it in a strange way.. the main idea is (high CO2 -> blood releases oxygen, low CO2 -> blood keeps oxygen). My thoughts were that the more oxygen we can stick into the blood the more will collect in the veins and tissues, as MarcinB said. It won't increase O2 in the arterial blood but will significantly increase O2 everywhere else. What I don't agree with is that we can never use it again, our CO2 will rise back to normal levels at the end of the dive and our blood looses the strong affinity with O2 allowing it to be consumed. In theory (Bohr research) our muscles will be allowed to consume less O2 the more alkaline our blood is. So if we return to normal CO2 levels at the end of the dive, with less Blood O2 desaturation at the begging wouldn't that be a good thing. That's already proven stuff, what we as freedivers as are worried about is O2 desaturation on the brain and how blood PH affects that. Again, during max hyperventilated statics I feels buzzy (hypoxic euphoria) for 3-4 mins, then it goes away, same in DYN, buzzy for 50m then it goes away. My feeling is that my brain is getting slightly less O2 to start with but after the CO2 builds up again everything goes back to normal. This happens also during 20m slow dives with hangs and deep(ish) CWT. again, less initial consumption of O2 ugh normal consumption at the end.

I was Initially worried the borh effect stuff would have an bigger effect with large pressure changes (shallow water BO). But again, no difference even on 70-74m VWT dives with very low CO2 production, all i can say is 74 with HV felt a lot easier than 70 without HV. Neither dive had any urge to breath at all, but w/HV the recovery felt much cleaner and 100% clear minded breaking the surface as opposed to slightly foggy on the noHV.

And finally, I'm not really sure about where my hypoxic limits actually are. This experimentation all started because the best stretch for packing is long packed statics. I was using HV to do this (4:00 no contractions is way better than 4:00 with 2:00 of contractions). It was only when I got hold of a pulse-Ox that I noticed I was ending with about 10% higher O2 than 4:00 without or even with minor HV. The best results (highest O2) came when I couldn't feel my face. Figured why not give it a go in depth. So since I've never been close to LMC in depth I'm not sure about the actual O2 levels, all I feel is that its easier. My only real evidence is that with HV I can do more reps of a particular depth or dive time before performance starts to fall off.

So, any suggestions on how to test this properly, not based on feeling of recovery? Is there a reliable, and not super expensive, way to test O2 levels on/after deep dives? Or if the total heart beats theory gets more traction I could eventually test that way.
 
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psimian

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I think the problem is that the question we want to answer is "When will I lose consciousness?" and we don't have enough information about how the various stats we can measure (O2, HR, etc.) relate to that threshold.

Here's a question: Is there any way to safely push a dive all the way to the point of blackout in order to collect the data we really need? The loss of consciousness is not harmful by itself since your body will attempt to start breathing again as soon as you stop consciously suppressing the respiratory reflex. As long as you get your O2 levels back up quickly, there's no risk of brain damage. (source: http://www.anesthesiaweb.org/hypoxia.php)

I'm imagining something like this: Complete a normal dive within safe limits; right before you surface, flood your mask with cold water to keep DR going. After surfacing, hold one arm overhead until loss of consciousness. Dropping the arm will be a very clear signal that you are losing motor control. As long as you have your buddy holding on to you after you surface, the risk should be negligible since LMC happens well before O2 levels are low enough to threaten the brain. I'd want to have supplemental O2 standing by on the surface, and several safety divers, but it should be possible to test with minimal risk.

Obviously this won't be a perfect representation of what would have happened if you had still been diving, since your O2 usage will change once you stop moving. But, it should still be a useful relative metric, and if we could analyze blood pressure, HR, and SpO2 during the process it might be possible to identify some pattern that signals imminent blackout.
 

cdavis

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Just the kind of bass-ackward, out of the box thinking that can sometimes lead to major advances in understanding, especially in an area a poorly understood as freediving physiology. Kudos for testing the ideas.

There is a little bit of historical support for the HV approach. In the early days of freediving spearfishing in the Med, extreme HV was gospel; divers did a lot of it and dived both deep and long. At the same time I've never seen any data to suggest that there were more BOs on those days. Given current gospel, I would have expected many more BOs, enough to be noticed by divers.

Differences among divers can be both internal and external, the kind of diving being done. For example, I have been diving FRC (half lung) for almost a decade. It works great for me, diving 40-90 ft, 1.8-2.0 minute dives. Gives me more comfortable dives, a little faster recovery and expecially, much longer dive times. Nathan, diving much deeper and longer, found something very different. HV is probably similar.

My immediate reaction to out of the box ideas like this is "how can I adapt this to improve my diving?" Jury is still out, but I'll be watching with great interest.
 
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Nathan Vinski

Nathan Vinski

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@cdavis Having both followed a lot of Eric's stuff I guess we appreciate "bass-ackward" haha. Also.. if you are looking for a way to adapt this to you own diving, HV doesn't work for normal weighted FRC dives, where higher CO2 has its value. However I was doing 30-35m FRC repeats to work EQ with no weight and no Freefall. Much easier (more possible reps of x depth before performance falls off) with HV where the initial CO2 production balances out the initial low levels. With normal weighting, 5m neutral, and regular FRC minimal breathup 4 reps of that depth is possible. With no freefall/no weight and HV, 7 were possible before performance fell. Again, I'm not currently properly adapted to FRC diving but maybe there's some value in less CO2 for very active starts where ending CO2 will be normal again.

And yeah, freediving physiology research has only been surface-scratched, we know almost nothing.

Looking at another sport that I spent a while training, long distance running. Until very recently everyone stepped heel->toe. Now the field is split 50/50, some with the traditional step, and some who skip the heel and land on the ball of the foot. Some research suggests the new approach is less prone to injuries but if you dig there's 0 evidence to support that claim, both have similar rates of slightly different injuries. Looking at the top 10 runners, you can again make no claims, they are relatively split 50/50 between the two styles.

if you look back a few years when Martin and Herbert were the 2 80-90m WR contenders, one hyperventilated like crazy, the other started on max CO2. Different approaches for 2 different people with different training styles. They both continued to the 120s with opposite breathups.

Mostly I think the taboo of HV is due to the education material. I do 100% agree that no one should be taught to HV when they start diving as the margin for error is greatly reduced and they are completely unaware of their limits. Eventually every diver starts to know themselves through training and then intelligent (1 variable at a time) experimentation can start to happen.

@psimian any ideas on how to test without reaching LMC? Despite the topic of this tread my #1 is safety and purposely reaching B.O or even LMC isn't an option for me. There's a reason I've kept the performances to below 3:15 on 20m and 55m CWT. I know those dives lower my O2 levels but I'm still very far from B.O which gives me a good margin to base my sensations on feeling. Otherwise I would, with my old approach, just go 2m deeper each time until I LMC'd then repeat the process with HV + no freefall and see what gets me deeper.
 
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Nathan Vinski

Nathan Vinski

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Just a little thing to add, from Fred Lemaitre's freediving physiology book "apnée: de la théorie à la pratique" unfortunately not yet translated into English..

Page 96-97. The Badjau tribal divers (from the recent enlarged spleen study) performed about 4-5 mins of hyperventilation before a dive. Most dives measured were an average of 2:00 long.

Page 168. Most marine mammals modify the rate of their breathing depending on the expected effort of the dive. The longer or deeper the animals expected to dive, the faster they would breath in the minutes preceding the dive.

Pages: 284-287. CO2 levels are not a good predictor or maximum performance. Evidence suggests the main disadvantage is delayed warning signals with decrease the effort needed to reach BO, but not much evidence to suggest we will reach BO sooner. So much more dangerous if you aren't in tune with other warning signs but no significant affects on actual performance.
 
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psimian

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I'm basing most of my ideas on anesthesiology research since those people have the most hard data on what happens when you lose/regain consciousness, and a little bit from military research into the effects of hypoxia on pilots. The military research is closer to the freediving situation, but it seems mostly concerned with keeping pilots as far away from the consciousness threshold as possible (for obvious reasons).

For reference, here's slide from a talk I gave a while back on freediving. I'm sure you have all seen this info before:
Hypoxia.jpg

The SpO2 numbers here are based on dry-land studies and don't take into account DR, Bohr Effect, hypoxic training, and all of the other freediving related effects. But, the order in which the neurological symptoms appear will remain constant regardless of the situation.

We're looking for ways to detect the sympotoms of moderate to severe hypoxia just before the cerebral cortex starts to shut down. Here's what I know about the various means of identifying each symptom:

Altered vision due to loss of O2 in retina:
The retina has the highest oxygen demand of any tissue in the body, and is therefor the first thing to fail under hypoxic conditions. Night vision goes first, then color vision, then black and white. Eye tracking performance decreases and reaction time increases continuously as O2 levels drop.
  1. Test the retina response directly by using a Visual Evoked Potential (place electrodes near the eye and shine lights at it), but this will be difficult to do in the water.
  2. Test night vision by making a mask with one eye blacked out to allow for complete dark adjustment. Periodically blink a very dim light in front of that eye, and look for the point at which it is no longer detectable. Getting complete darkness inside a mask will be difficult, as will getting a light that is dim enough.
  3. Test visual reaction time by building a small led display into one side of a mask. Use a camera to track eye movements in response to dot moving around on the monitor. This is a somewhat complicated build, but all of the techniques are well established. It would only be a matter of figuring out how to waterproof the camera/monitor setup. One potential problem with using this during non-static dives is diver distraction causing erroneous/noisy data.
Altered mental function:
  1. FMRI. Unfortunately only works in a laboratory setting.
  2. EEG. Might be interesting to see how brain activity while diving correlates with subjective experience, but anesthesiologists have not found any EEG markers that indicate consciousness, or loss thereof.
  3. Test cerebral function by having the diver solve simple problems, e.g. count backwards from 1000 by 3's. It's cheap and easy, but might only work for static dives. Even then, the act of having to respond to questions by writing on a slate will affect dive performance.
Altered motor function:
  1. This is the one I already proposed, since LMC tends to be the final warning of impending blackout. Rather than holding an arm overhead, it might be marginally safer to have the diver do something like raise fingers in a repeating pattern (r. thumb, l. thumb, r. index, l. index). Keeping track of the pattern will test mental function, and the ability to initiate new motor action fails slightly before the ability to maintain ongoing actions.
Cyanosis:
  1. Measuring this amounts to using a pulse-oximeter. It's worth tracking, but doesn't seem to be a reliable indicator on its own.
Personally, I think the problem solving test and the eye movement test have the most promise if you want to avoid going all the way to LMC. The problem solving test would just be a matter of coming up with a question protocol that would have as little impact on the dive as possible.
 

psimian

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Oh, and I should point out that I keep talking about O2 numbers even though this is a CO2 thread becuase I assume what we're all interested in is how CO2 levels achieved by hyperventilating affect our ability to remain conscious and functioning during different diving conditions.
 
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Nathan Vinski

Nathan Vinski

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Oh, and I should point out that I keep talking about O2 numbers even though this is a CO2 thread becuase I assume what we're all interested in is how CO2 levels achieved by hyperventilating affect our ability to remain conscious and functioning during different diving conditions.
Yes, O2 level is all that really matters. My "hard numbers" that I'm using to support my experimentation are;

  1. (2 years ago) Day 1: HV until loss of feeling in arms, legs, and face -> dry FRC static + (active stair climb at 4:00 for 20s) Total time 4:37 stop at first contraction with NO (seriously clean as a whistle) signs of hypoxia... Day 2: Normal tidal breath up -> FRC (only static) -> dry LMC at 3:48. My thoughts are that even slight day to day metabolic differences couldn't make that big of a difference in performance considering the longer one involved running up the stairs and no real recovery breaths. I was on vacation and had no extra stress the second day and did both before breakfast so variables were quite limited.
  2. With my recent (5-6 weeks ago) tests I was going 4:00 minute statics with 10 packs as a stretch for packing and tried them with a pulse-Oxi. Day 1: extreme HV (no feeling in face, arms, feet) Lowest registered O2: 93%. Day 2: Tidal breathing + 4 purges Lowest registered O2, 86%. Day 3: extreme HV, Lowest registered O2, 94%. Day 4: Tidal breathing +4 purges Lowest registered O2, 82%.
My initial thought from the 4:00 statics was that less vasoconstriction from less CO2 was giving a higher O2 reading.. So I tested in depth and you've read about that already.. So yeah, my ideas are about potentially collecting gas samples from exhaled air, maybe testing HR+total heart beats if I find a good monitor. What I would be most curious to see (probably the hardest thing to test) is how much more O2 I can store in the veins with HV, and how well I recover the Bohr effect so that I get a use of the Extra O2. It seems that my body is doing this quite well but a definitive measurement method would be interesting.

What interesting is that best results on deep dives with HV are when I skip the freefall, I have some hypothesis as to why this is, but need to use my dive computer a bit more before I make any claims.
 

MarcinB

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Oct 26, 2012
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What I would be most curious to see (probably the hardest thing to test) is how much more O2 I can store in the veins with HV
Yes, it's really difficult to measure, it requires insertion of a catheter into the pulmonary artery. There's one study where it was measured in conscious subjects after moderate voluntary hyperventilation. Oxygen saturation of the mixed venous blood rose by 3-6%.
 

psimian

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Jul 12, 2015
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Good point about "available O2" vs what shows on the pulse-ox. This is a good argument for some kind of ongoing cognition test while diving.

I wonder if it could be as simple as some kind of color vision test? O2 and CO2 levels affect color discrimination in well documented ways. There's enough color acuity tests online that I can probably come up with a way to test this on dry land while doing CO2 tables or some similar drill. Basically, see if my color vision changes in a predictable way at the end of a breath hold. If it works, then try to come up with some kind of mask-mounted test device. Something like: a small monitor shows two color blocks, you look at the one that is more red, and a camera registers your answer.

If I'm reading this right https://pdfs.semanticscholar.org/6646/fc82ea057b21f052335bbff8c8bf9bdd3fd6.pdf

In terms of increased sensitivity we have
Hypoxia = Red
Hyperoxia = Green

Hypocapnia = Green
Hypercapnia = Red

Hyperoxia isn't possible at sea level unless you're breathing supplemental O2 (correct me if I'm wrong), so any visual changes during HV are due to hypocapnia.
 
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Nathan Vinski

Nathan Vinski

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Apr 19, 2015
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Good point about "available O2" vs what shows on the pulse-ox. This is a good argument for some kind of ongoing cognition test while diving.

I wonder if it could be as simple as some kind of color vision test? O2 and CO2 levels affect color discrimination in well documented ways. There's enough color acuity tests online that I can probably come up with a way to test this on dry land while doing CO2 tables or some similar drill. Basically, see if my color vision changes in a predictable way at the end of a breath hold. If it works, then try to come up with some kind of mask-mounted test device. Something like: a small monitor shows two color blocks, you look at the one that is more red, and a camera registers your answer.

If I'm reading this right https://pdfs.semanticscholar.org/6646/fc82ea057b21f052335bbff8c8bf9bdd3fd6.pdf

In terms of increased sensitivity we have
Hypoxia = Red
Hyperoxia = Green

Hypocapnia = Green
Hypercapnia = Red

Hyperoxia isn't possible at sea level unless you're breathing supplemental O2 (correct me if I'm wrong), so any visual changes during HV are due to hypocapnia.
Interesting.. my usual warning sign for hypoxia is a slight orange tinge in my vision. Even eyes closed I get some orangeness when I'm approaching the limit. I'll pay more attention but I haven't noticed any colour changes from HV.
 
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Nathan Vinski

Nathan Vinski

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Apr 19, 2015
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it took a while to find because if forgot the title but lots of good information in this thread..

https://forums.deeperblue.com/threads/co2-compartment-hypothesis.41696/

My thoughts on how it applies to me are that my natural CO2 buffering is bad. When my training was going well the latest I could ever push my contractions with normal breathing was 1:45. 4:45 was really fun :/ On days where I was even slightly unrelaxed or hadn't been training properly that went down to around 1:20. Other Eric Fattah experiments that I tried (eat/drink baking soda) did help a little bit, but also made me feel quite sick after so I couldn't use that.

Reasons for this are most likely genetic and partly diet, I eat a lot of meat and carbohydrates, and probably too much cake. basically I don't eat a lot of bi-carbonate (buffer) forming foods. And considering that it only takes around 15 forced+full inhales + passive exhales for me to get severe symptoms of hypocapnia (further evidence of low buffers) and even on statics starting on the edge of HV BO I still get contractions before 5:00 I must be building enough acid to negate the negatives of high alkalinity.

Attached is another Eric Hypothesis.. hadn't read that before but the thought process supports my thinking that using alkaline blood to our advantage to oxygenate the veins and limit O2 desaturation at the beginning of the dive might help as long as we build back acidity to use the O2 near the end.. Since my body seems to build acidity quite quickly, this doesn't cause any issues for me.

Screen Shot 2018-05-04 at 7.57.00 PM.jpg
 
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psimian

Member
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This is awesome! I found something that looks really promising as method for evaluating CO2/O2 effects on the retina. I was thinking about the Ishihara Test for color blindness, and was wondering if there was a way to a computerized version. The difficulty is that computer monitors can't emit true monochromatic light, so the test doesn't work quite as well.

Then I found this: http://www.colorblindcheck.com/

It's an android app that apparently shows promising results for detecting color blindness, though it hasn't been validated yet. Even better, the method it uses could easily be adapted to the monitor + eye movement method I mentioned earlier. I took the test under normal conditions and got a perfect score. I then hyperventilated to the point of tingling hands & feet, took it again, and came up as partially color blind. Because of how the test is structured, it's unclear how much of this is due to impaired cognitive function (i.e. slowed reaction time), and how much is due to changes in the retina, but for our purposes it really doesn't matter since either one is an indication that something is going wrong.
 
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