Inhale & Exhale PO2 testing with Seb

[ADR]

Hi DBers,

Seb went back home today :waterwork after 5 days in sydney running an exhale clinic and doing some inhale and exhale PO2 testing on some local divers. Attached are a couple of shots on my little boat (kermit) with the sampling gear. On surfacing we had to exhale to remove the dead air space and then he would capture the last 60ml of air from our lungs for testing. I'll let Seb talk to the results but can say some really interesting numbers came from comparing the same dives (time & depth) for inhale and exhale.

Andy

 

[pyro]

Sorry to sound stupid but what's po2?

 

[ADR]

Pyro,

The best thing about this site is there are no stupid questions...it's sort of one of the unwritten rules!

PO2 is oxygen partial pressure. That is in air it is generally 20.9% at 1 atmosphere and in the lungs of a diver close to blackout on the surface is about 5% (I think that's right)

regards

 

[Walrus]

Hi Andy,
well the next may be silly also
With the testing you guys were doing, you mentioned you were blowing out so much air then sampling a small amount from the rest. From what I can see into a syrynge?
When comparing PO2 of an inhale dive vs an exhale dive - if the diver came up with say %10 for both, then doesn't volume become an issue too ?
ie a diver with a half lung full of %10 has less air left then the diver with a full lung of %10.

Cheers,
Wal

 

[ADR]

Yep, but the volume doesn't matter on surfacing as it's still 10% PO2 in both cases. ie. it's the PO2 that keeps you from blackout rather than the volume. The volume will determine how fast the PO2 drops through the dive(all other things being equal which seb will argue they are not but that is another discussion)

......by the way do you know any freedivers with SVG skills? We need someone right now for a few days :duh - just kidding

 

[Walrus]

Hi Andy,
in that scenario, having %10 with both means that with full lungs the diver has twice the available oxygen in the lungs vs FRC. Therefore at the end of the dive there was more left in reserve.

If you project forward and assume that oxygen consumption will keep going with the same trend in both cases you are no longer being objective. Dr Peter Lindholm has done tests on freedivers, on a exercise bike underwater, looking at blood pressure, Heart rate and O2 saturation. There is a very similar result then what we did with the statics on a Pulse Oxy. On inhale the Bradycardia doesn't really kick in until over halfway. The shift of muscles towards Anaerobic mechanisms happens more at the end. In short on an inhale dive, the first part of the dive is much less oxygen efficient then the last part of the dive. My guess is with FRC it is a little more linear once the initial Bradycardia has kicked in, which should happen early in the dive.

It would be far more objective to do close to maximum dives for both FRC and inhale, then compare.

P.S. In Hawaii I will be focusing on training, so if you want to talk Theory I will just have to send you Bill's way.

Cheers,
Wal

 

[Bill]

He'll probably be focused for a few days all right.
Aloha
Bill

 

[ADR]

Wal,

I don't entirely agree with your statement "twice the available oxygen" and let me give you some extreme examples(created to suit my arguement ) to explain.

Assume end of dive for both of these
eg 1. Forced exhale with reverse packing
end of dive PO2 6% lung volume of 1.5 liters (amount of lung oxygen 90ml)

eg2. Fully packed inhale
end of dive PO2 3% lung volume 10 liters (amount of oxygen 300ml)

...."see more oxygen I hear you say" and for the above example you are correct but it is irrelavent because although diver 2 might have over 3 times as much O2 by volume the PO2 of 3% means they would have blacked out.

So getting back to your example it doesn't really matter as both had 10% and are back on the surface and breathing again regardless of the fact that the inhale has twice the volume. The test results (I wish you could have made it) don't suggest they will both arrive back with the same PO2 and that is what really matters once you are back on the surface rather than the volume.

The volume is one of the key variables that impacts what the PO2 will do through the course of the dive (ie how quickly it will drop) and this is really the interesting point. The inhale world contends that the PO2 will drop faster with exhale as all other variables are equal and you are starting with half the O2 store, whereas the exhale world will contend that the other variables have a bigger impact than the decreased volume and therefore you arrive back with a smaller volume but with a PO2 that will keep you conscious rather than a larger volume that won't.

I'm not from either world or maybe I'm stuck halfway in between....my results where the least supportive of exhale for the group.

In terms of discussing it in Hawaii it makes no difference to me either way as I enjoy your company with or without this topic ... and would probably rather just going diving with you in those warm blue waters

btw - Hawaii for me will be inhale for all events.....after Hawaii who knows :duh

 

[Walrus]

Nah I'll just let you bug Martin & Kirk with this FRC stuff instead

I just meant that the results would be more objective when you dive closer to the limit. For the reasons I mentioned above, I think dives returning with a higher PO2, will tend to be favoured towards exhale. (This would be more likely in the case of beginner divers that aren't pushing too much). Say the case with the diver returning with %12 PO2, in the inhale case perhaps the dive reflex has only just started kicking in, whereas for exhale it occured far earlier in the dive. So for a shorter dive in that case it may be for that diver exhale is better. But then if the same diver pushes towards their limit, the results are different.

You can't assume that the rate that PO2 drops thru the dive is linear. That's what I'm trying to get at, on an inhale dive you get better O2 efficiency towards the end, not at the beginning. Look at the heartrate plot vs SAO2 for your static.

Yay Hawaii!
The water will finally be as warm as the pool I train in.

 

[ADR]

I'm going to ask Martin and Kirk about the results of some tests I'll perform between now and then and I'll let you know what they think. hopefully I won't get kicked off the course!!

We only looked at 1 min dives to 11m on inhale and exhale with 4min rests between them. From a deductive reasoning standpoint that allows some firm conclusions to be made but it would require a switch to inductive reasoning to make an overall claim on inhale vs exhale from our test results alone and the problem with this is that inductive reasoning while pwerful can be more easily incorrect. I personally wouldn't make a conclusion about max effort dives from the tests we carried out(either for or against). Additionally given only 4 test subjects I'm not sure we can claim conclusive proof for the majority of divers even for the sort of dives that were performed. What we can say is that the results suggest something (inductive reasoning) that is worth looking into and verifying. Seb is in the process of doing this with more tests and more subjects. I wish I could just share the results as they were eyebrow raising but given that this is the basis of Seb's thesis I think it would be inappropriate for me to do so. I would however like you to perform the same tests we did with me and see for youself the results so that you can come to your own conclusions.

One thing that has really stood out for me through the process is the power of doing tests yourself to validate things. I have read lots of posts on this site and picked up awesome information that I then take for granted.....testing these very theories and hypothsese and seeing the results makes them very tangible....and you don't need a PHD or expensive equipment to do a lot of it One of the key elements to our PO2 testing after trying many alternatives was a condom :duh - he will probably kill me for letting that cat out of the bag!!

You said

Say the case with the diver returning with %12 PO2, in the inhale case perhaps the dive reflex has only just started kicking in, whereas for exhale it occured far earlier in the dive. So for a shorter dive in that case it may be for that diver exhale is better. But then if the same diver pushes towards their limit, the results are different."

This is an educated hypothesis that may or may not be correct....why don't you and I test it? ........when we get back from Hawaii

 

[Walrus]

Well with 1 min dives no wonder. I'd be happy to try a 3 min dive on inhale, but someone would have to get my carcass off the bottom if I tried that on exhale. :duh
I agree that the results are interesting, but still think you should look at a whole dive, not the first half of a dive. Like I said I suspect this would heavily bias the results in favour of exhale.

Actually the part I mentioned about inhale being more O2 efficient at the end of the dive is not an educated guess. Dr Peter Linholm studied freedivers doing a simulated dive. They pedalled at a constant rate whilst holding their breath. The Bradycardia was stronger at the end of the simulated dive, (just like for a static - look at your graph!). Whilst keeping the same energy output, the rate of O2 consumption did decrease somewhat as the muscles starting using more anaerobic supplies. I thought this was common knowledge ? Look up the thread about "sprinting at the end of a dynamic or dive".
The simulation is probably closer to dynamic, but still get an idea from it for inhale dives in general.

I think it's good he is doing these tests, and hope he does more, (preferably looking at longer dives vs short ones).


Cheers,
Wal

 

[ADR]

My comments on "educated guess" relates not to Dr Linholm conclusions that you spoke about (yes they are common knowledge) but your subsequent hypothesis relating to O2 consumption comparisons to exhale and end PO2 points......did Dr Linholm test exhale as well or are you guessing? ...I'm happy to be corrected on this if he did

Wal this thread was never intended to be an inhale vs exhale thread, that is why I intentionally entitled it Inhale & Exhale. You draw many unproven conclusions from your knowledge and I'm offering you a chance to experiment with those conclusions with me. My mind is open on the subjest as I said earlier, yours seems rather closed on the subject and I don't know why this is such a hot topic for you.

The point of this round of tests was to look at unstressed repeat dives NOT max attempts(he has already gathered data on max attempts). Nowhere have I actually made any statements that this is what we were testing or that it made any conclusions relating to it so I'm at a loss as why you are dragging it in that direction.

Anyway I hope you will jump into kermit and come a dabble in this stuff with me.

 

[sebastien murat]

Walter,

I understand and appreciate your reasoning but there are several aspects which you may be unfamiliar with: inhales result in an increased incidence of ascent tachycardia which is related to peripheral reperfusion and large decreases in PaO2. Secondly, a rexpanding lung volume that results in +ve intrathorcic pressures impedes venous return, potentially increasing the likelyhood of cerebral ischaemic hypoxia and a greater need to switch over to anaerobic metabolims. Thirdly, the dive response is absolutely greater with 'exhales' and is also progressive in time (not just with inhales). Fourthly, regarding linearity of VO2 (i.e., O2 uptake): VO2 is not always indicative of what is happening at the tissues. VO2 is typically measured at at the lungs, with littele consideration for pulmonary perfusion and a-vO2 differences.

The reason I decided to test shorter dives was because they're more representative of the types of serial dives undertaken by spearfishers. In regards to max dives (not referring to statics), I've done both types and provided you have an adequate DR they are more efficient


Seb

 

[sebastien murat]

Here's a very simple trial I carried out this morning (attached) for those with some interest with the exhale vs. inhale issue.

Although there is only an absolute difference in PO2 of 1.3% between the two startegies, if you consider that alveolar PO2 is ~13.2% under resting, non-apnoeic conditions, this corresponds to ~a 10% relative difference in PO2 between the two.

Seb
Townsville, Aust.

PS: Andy, I'm collating your data...you should have it pm