A Few Thoughts on Tech Freediving

Well Dr Alun,

I remember reading comments like that about 4-5 years ago, and thinking - Wow! Then I realised that it was more of an issue of lung tissue becoming erect, rather than actually filling plasma.

Now, if I jog my feeble memory back into physiology mode - It would take a change in osmotic pressure for plasma to enter the lung air-spaces - and a big one at that. Capilliaires would rupture before the necessary physical pressure was reached to force blood plasma through at the kind of rate implied here.

People may compare this scenario to pulmonary oedema (sp?) at extreme altitudes - but that needs time to occur, or an extremely low pressure - and it is different. In that case the absolute pressure drops externally and the internal blood pressure tries to remain as it is. Thereby making an increased gradient.

In our instance - the pressure of air in the lungs gets higher and the RELATIVE difference between absolute blood pressure and absolute lung air pressure reduces. To get any transfer of blood plasma across the membrane there would need to be a big resistance to compression by the ribs and diaphragm which would allow the blood pressure to be high and the lung pressure to be lower than normal.

Alternatively, there could be an alteration in membrane function at pressure. This does happen, but I seem to remember that it needs a lot more absolute pressure i.e. at least 200 bar.

:hungover

i've now read the emails...

he mentions some benefits which make sense... such as reduced DCI/narcosis/metabolism.

he mentions SWB, but i would consider that neither here nor there, because if you're diving close to your limit, you're going to black out close to the surface by definition, regardless of the actual mechanism.

with HR as low as he's quoting, there must be an increased risk of blackout from stagnant flow of blood in the brain. i've no idea what the HR value would be though- probably under 10bpm?

he doesn't say anything about equalising pressure within the lung... which could well be the overall limiting factor.

there is no mention of having actually completed any deep empty lung dives, but that certainly seems to be his intention. from what i can gather from the emails, it's all theory at this stage.

this could revolutionise freediving- if he can actually pull it off....
thanks for telling us about this loopy!


alun

hi

Alun did he say that he can get hi heart rate to below 10bpm or he thinks it will when he dives. Thats impressive 10bpm.

cheers

he predicts a value of 6-10bpm based on his RHR of 35-ish. i've no idea how he was able to make that prediction though. it can't be an easy thing to actually measure at extreme pressures.

alun

Lowest safe Heart rate

Good point Alun:

Assuming that under extreme blood shift it takes 2 heart beats worth to flush the brain (total guess), and suggesting a 10 second lag between cessation of blood flow and black out:

A minimum heart rate of 12 bpm would be the minimum.

A lot of these quoted minimum heart rates are a load of nonsense - Seb himself said it was a guess - and those that have actually been measured as 7-10 beats per minute are done from the maximum interpulse duration - i.e. if there was a 10 second gap between heart beats but normally the gap is 3 seconds - the heart rate should be 20 - but they might quote 6 bpm...

The minimum heart rate to avoid losing consciousness would depend on whether you inhaled or exhaled before going down. If you inhaled, then at extreme depth (i.e. 100m+) you will have a huge (nearly toxic) amount of O2 dissolved directly into the blood plasma. This means that your heart could stop beating for a huge amount of time without loss of consciousness. If, however, you exhale and go down to the same depth, you don't have that huge O2 level, so a few seconds would be about the max you could last between heart beats.

They say that under 'ordinary' conditions on land, an 'ordinary' person will black out in 6-7 seconds if you strangle them and totally cut off the brain blood supply -- but, almost all of that energy comes from ATP/CP; they say you only have a couple of seconds of O2 in your brain blood supply itself (if flow is stopped).

Of course, at depth (and cold), your brain is probably not consuming as much O2.


Eric Fattah
BC, Canada

hi

From what im hearing Seb is thinking about doing some pretty dangerous stuff, agreed. Hope he takes it easy.

cheers