Inhale & Exhale PO2 testing with Seb

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,

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

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

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

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."

Click to expand...

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

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.