AAS - Teaching real life situation

[Andy War]

Hope someone can clarify this for definate please.

When teaching AAS as a real life out of air situation.
Should it be taught that the recipient when swimming towards the donor to grab that vital octopus, should be exhaling the air that they have after their last gasp from their own reg when swimming horizontally NOT ASENDING (we all know the score with that one).

Most people i have spoke to say they would not exhale until they have the octopus when swimming horizontally.

Can anyone confirm if the Instructor Training manual or recent amendments detail this situation?

[TerryH]

Hope someone can clarify this for definate please.

When teaching AAS as a real life out of air situation.
Should it be taught that the recipient when swimming towards the donor to grab that vital octopus, should be exhaling the air that they have after their last gasp from their own reg when swimming horizontally NOT ASENDING (we all know the score with that one).

Most people i have spoke to say they would not exhale until they have the octopus when swimming horizontally.

Can anyone confirm if the Instructor Training manual or recent amendments detail this situation?

Cant find anything on this in the manual, but logic says
that if you are swimming over to your buddy then you will be
horizontal and so no need to breathe out. The only time you
will is if your buddy is significantly above you.

It's always a case of get air, get settled, then go home. So
you have three stages before you even think about going
vertical.

HTH
TerryH

[Ariel]

--- snip ---
Most people i have spoke to say they would not exhale until they have the octopus when swimming horizontally.

Can anyone confirm if the Instructor Training manual or recent amendments detail this situation?
--- snip ---
I just looked at the 2002 manual, and no mention is made here about exhaling (either for or against) whilst attempting to acquire the octopus. However, under the previous syllabus, when teaching buddy breathing (shared main regulator) the lesson included instructions NOT to hold your breath whilst waiting for the DV to come back. We also taught that during the DV recovery lesson the student should NOT hold their breath. It seems logical then that the AAS lesson should also stress NOT holding your breath under water.

IMHO under stress it is better to have a single rule to remember, rather than a situational rule - breath holding whilst not ascending is OK in principal, but can become breath holding during ascent, which is definitely not OK. Keeping the rule simple (breathe out - don't breath hold) should help to avoid an AAS incident.

In a real event the OOA diver is likely to have less-than-full lungs at the point where they discover there is no more air in their primary supply. Pointing this out, and inviting students to swim (horizontally) after breathing out, and seeing how far they get before becoming uncomfortable / needing to breathe (whilst keeping the DV in their mouth of course!) is also a good lesson reminder about not straying too far from your buddy, for both sakes!

Safe diving,

Ariel

[matts]

Hope someone can clarify this for definate please.

Not me, I can give you some points to consider but you are the instructor and it is up to you what you teach IMHO. If I am not sure what is the best thing to teach and there is no clear guidance I will try a few different ways and suggest the trainee does the same.

When teaching AAS as a real life out of air situation.
Should it be taught that the recipient when swimming towards the donor to grab that vital octopus, should be exhaling the air that they have after their last gasp from their own reg when swimming horizontally NOT ASENDING (we all know the score with that one).

Simple logic may suggest that holding that last breath is a good idea, our physiology is not always simple or logical though ;-) The impetus to breathe is caused by CO2 build up, the danger is CO2 blackout not lack of Oxygen. So a gentle and controlled out breath may help reduce panic symptoms and extend what is achievable on that last gasp by lowering CO2 build up.

Have a look at the Oral Infaltion thread further down the page.

I definitely recommend a few snorkeling experiments as the results can be quite surprising.

Another thing you can try to make an AAS drill more realistic, particualrly during Sports and Dive Leader, is to suggest the trainee comences the swim after breathing out.

HTH

[Andy Wade]

:=Hope someone can clarify this for definate please.

Not me, I can give you some points to consider but you are the instructor and it is up to you what you teach IMHO. If I am not sure what is the best thing to teach and there is no clear guidance I will try a few different ways and suggest the trainee does the same.

:=When teaching AAS as a real life out of air situation.
:=Should it be taught that the recipient when swimming towards the donor to grab that vital octopus, should be exhaling the air that they have after their last gasp from their own reg when swimming horizontally NOT ASENDING (we all know the score with that one).

Simple logic may suggest that holding that last breath is a good idea, our physiology is not always simple or logical though ;-) The impetus to breathe is caused by CO2 build up, the danger is CO2 blackout not lack of Oxygen. So a gentle and controlled out breath may help reduce panic symptoms and extend what is achievable on that last gasp by lowering CO2 build up.

Have a look at the Oral Infaltion thread further down the page.

I definitely recommend a few snorkeling experiments as the results can be quite surprising.

Yup, I can confirm that for ages in our branch I used to beat hands down even the fittest members of the branch in breath holding underwater swims simply because I slowly whistled out my air as I swam along, eventually they spotted what I was doing and my status as a 'breath holding god' disappeared...
Shucks. I knew it wouldn't last forever.
;-)

[iainmsmith]

Simple logic may suggest that holding that last breath is a good idea, our physiology is not always simple or logical though ;-) The impetus to breathe is caused by CO2 build up, the danger is CO2 blackout...

The what? I don't recall having heard of this phenomenon before. Could you elaborate, please?

Iain

[Andy Wade]

:=Simple logic may suggest that holding that last breath is a good idea, our physiology is not always simple or logical though ;-) The impetus to breathe is caused by CO2 build up, the danger is CO2 blackout...

The what? I don't recall having heard of this phenomenon before. Could you elaborate, please?


Oooh, hadn't spotted that, C02 blackout....
Surely it's hypoxic levels of O2 that could cause a blackout?


.

[janos]

CO2 blackout exists.

AIUI when breathing a high PPO2 of oxygen, the O2 can saturate the haemoglobin, and as CO2 is also transported by haemoglobin and cannot bind to it if it is saturated, the CO2 transport mechanism slows down (but does not stop) Also, the oxy-haemoglobin does not break down as the body's oxygen needs are satisfied (in the short term) by the O2 in the plasma, and because the trigger for oxy-haemoglobin breakdown is an increase in acidity due to dissolved CO2, which has got stuck (a technical term ;-) ) in the cell. Eventually, enough CO2 gets through to the plasma and the increase in acidity leads to a sudden breakdown of the oxy-haemoglobin leading to a large amount of available O2. This in turn causes severe narcotic effects and the tissue shuts down.

Because of the mechanism, the parts of the body use the most oxygen (such as the brain) are most likely to shut down. Ie you pass out.

There are a few interesting papers by Angel (amongst others). on differential inert gas narcosis. Have a google.

Janos

[iainmsmith]

I should start by saying that my original response was perhaps inadequately phrased - CO2 blackout certainly can occur, though the mechanism is not quite as you describe. However, it does not make sense in the context in which it was originally mentioned. See below:

AIUI when breathing a high PPO2 of oxygen, the O2 can saturate the haemoglobin,

You mean a bit like it does when breathing air at atmospheric pressure?

and as CO2 is also transported by haemoglobin and cannot bind to it if it is saturated, the CO2 transport mechanism slows down (but does not stop)

As opposed to simply dissolving in the plasma or converting to bicarbonate (an process which occurs in the red blood cell and allows significant buffering of excess CO2 without significant changes in pH or PCO2)?

CO2 gets transported in three main ways: dissolved in plasma, bound to haemoglobin - carbaminohaemoglobin - and other plasma proteins and as bicarbonate. This latter mechanism is thought to normally account for 20% of CO2 transport, with a theoretical maximum of 30%.

Also, the oxy-haemoglobin does not break down as the body's oxygen needs are satisfied (in the short term) by the O2 in the plasma,

What pO2 do you have to breath in order to dissolve sufficient O2 in plasma to supply the body's needs without needing to use the Hb-O2 reservoir?

and because the trigger for oxy-haemoglobin breakdown is an increase in acidity due to dissolved CO2, which has got stuck (a technical term ;-) ) in the cell.

There are a number of factors which promote Hb-O2 dissociation. A low PO2 is one of them. As you say, an increased hydrogen ion concentration is another. As is an increase in 2,3-DPG concentration. In other words, it is rather more complicated than you suggest.

Eventually, enough CO2 gets through to the plasma and the increase in acidity leads to a sudden breakdown of the oxy-haemoglobin leading to a large amount of available O2. This in turn causes severe narcotic effects and the tissue shuts down.

This does not make physiological sense. A rise in plasma PCO2 is _not_ a "breakthrough" effect, neither is the release of O2 from Hb-O2. There then appears to be some confusion over the vasoconstricting effects of elevated pO2s (but remember, in the scenario you describe, the subject will be breathing hugely elevated PO2s in any case - at best, the PO2 will gradually drop until Hb-O2 starts dissociating - it's not going to drop then suddenly shoot up) "Tissue shut down" is _not_ a response to narcosis, nor will there be a sudden narcotic release of O2 from Hb.

However, responding to this did prompt me to pick up Kenneth Donald's "Oxygen & the Diver", in which CO2 blackout is described...

The original "Shallow Water Blackout" in oxygen-rebreathing divers was not as we tend to thing about it today in a snorkelling context (hyperventilation leading to reduced pCO2, therefore reduced stimulus to breath and pO2 dropping to a level inadequate to return to the surface before the desire to breath is noted). It was an unexpected problem noted when fin-swimmers used oxygen rebreathers in the range 0-6m. The same phenomenon (including the narcotic effects which preceed blackout) was reproduced in lab conditions by significant exertion while breathing oxygen through a large external dead space (ie rebreathing CO2). It was discovered that fin-swimmers were able to take up (and convert to CO2) far greater quantities of O2 than their booted predecessors. The absorption canisters in use at the time had not been designed for such significantly higher rates of CO2 delivery, hence the swimmers were rebreathing CO2. In other words, pCO2 can cause blackouts over a period of time if the diver is unable to eliminate sufficient of it,

However, returning to the context in which CO2 blackout was proposed: it is _extremely_ unlikely that a diver's will to hold his breath is going to overcome the hypercapnic drive to breath to the point that he passes out. Try it yourself...

Iain

[matts]

Thanks Iain/Janos, all very interesting and informative.

My original response was intentionally simple and I aplogise if you found it misleading as a result. My point was only that failure to ventilate the Alveolie leads to hypercapnia, the symptoms of which are panic, unconciousness and eventually death. The object of the explanation was to convey that while holding your last breath may sound logical, hypercapnia is likely to be the indirect cause of death well before all the O2 in the breath is metabolised.

However, returning to the context in which CO2 blackout was proposed: it is _extremely_ unlikely that a diver's will to hold his breath is going to overcome the hypercapnic drive to breath to the point that he passes out.

Just as a hypothetical point of interest, lets just say that someone did manage to surpress the urge to breathe indefinitely. Which would get them first, CO2 buildup leading to unconsciousness (hypercapnia), O2 starvation (hypoxia), or is it a combination of the two?

[iainmsmith]

Just as a hypothetical point of interest, lets just say that someone did manage to surpress the urge to breathe indefinitely. Which would get them first, CO2 buildup leading to unconsciousness (hypercapnia), O2 starvation (hypoxia), or is it a combination of the two?

Hypoxia.

Think of an over-hyperventilated freediver - they pass out from hypoxia after only a very few minutes. In contrast, if one were to start by breathing pure O2 and then to rebreath one's exhaled gas (thus avoiding hypoxia while increasing hypercapnia) the process of intoxication and unconsciousness will take somewhat longer. (This may be covered in CCR training? I haven't got my physiology notes to hand and can't remember the precise time scales involved)

In contrast, the subject who is simply holding a normal breath is (effectively) rebreathing his CO2 (albeit without breathing...if that makes sense!) while his blood oxygen level falls, just like the freediver.

Iain

[Andy Wade]

:=Just as a hypothetical point of interest, lets just say that someone did manage to surpress the urge to breathe indefinitely. Which would get them first, CO2 buildup leading to unconsciousness (hypercapnia), O2 starvation (hypoxia), or is it a combination of the two?

Hypoxia.

Think of an over-hyperventilated freediver - they pass out from hypoxia after only a very few minutes. In contrast, if one were to start by breathing pure O2 and then to rebreath one's exhaled gas (thus avoiding hypoxia while increasing hypercapnia) the process of intoxication and unconsciousness will take somewhat longer. (This may be covered in CCR training? I haven't got my physiology notes to hand and can't remember the precise time scales involved)

In contrast, the subject who is simply holding a normal breath is (effectively) rebreathing his CO2 (albeit without breathing...if that makes sense!) while his blood oxygen level falls, just like the freediver.


Look what happens when you go to work on a Saturday, a very interesting discussion occurs!
Thanks for explaining things a lot better that I ever could Iain.
Some very interesting points raised.
My money would have been on Hypoxia getting you before Hypercapnia.

My point would have been that if Hypercapnia affected divers that much, it would be explained far more than any dive manual covers, in fact IIRC some don't even mention it.
Although with the increased use of mixed gases and deeper depths being dived by a lot more people than say 5 years ago, maybe it should be explained a bit more for the average Joe diver to at least have a grasp of something they may come across one day.


.

[Nigel Hewitt]

Oooh, hadn't spotted that, C02 blackout....
Surely it's hypoxic levels of O2 that could cause a blackout?

Rebreather divers with acceptable O2 levels in the loop have allegedly blacked out with high CO2 with little or no warning. High CO2 at depth isn't like the breathlessness you get shallow or on the surface.

Interestingly, Gordon Henderson pointed out that a freediver in a Samba (shallow water blackout on ascent) does not show blue lips, the classic sign of low blood oxygen. He tentatively attributes the SWB to CO2. I have samba'ed and been grabbed by a safety diver and my son confirmed I did not have blue lips. I had way overdone it and ascending through 15m was fighting the CO2 driven breathing reflexes.

[Andy Wade]

:=Oooh, hadn't spotted that, C02 blackout....
:=Surely it's hypoxic levels of O2 that could cause a blackout?

Rebreather divers with acceptable O2 levels in the loop have allegedly blacked out with high CO2 with little or no warning. High CO2 at depth isn't like the breathlessness you get shallow or on the surface.

Interestingly, Gordon Henderson pointed out that a freediver in a Samba (shallow water blackout on ascent) does not show blue lips, the classic sign of low blood oxygen. He tentatively attributes the SWB to CO2. I have samba'ed and been grabbed by a safety diver and my son confirmed I did not have blue lips. I had way overdone it and ascending through 15m was fighting the CO2 driven breathing reflexes.

So, someone likely to be susceptible to hypercapnia because of the type of diving and gas mixes they are using, should be aware of this anyway? Whereas someone running out of air on a shallow air or nitrox dive, probably doesn't need to worry too much, and can whistle out their remaining air whilst swimming for their buddy, to reduce their (increasingly stronger) urge to breathe caused by CO2 build up?
I know it works because I've tried it out in the pool. I can definitely swim further when I don't hold my breath, but slowly whistle out the air.

I remember we used to strongly urge people not to over-hyperventilate before a snorkel dive as they could end up passing out at or near the surface after the snorkel dive.
This would be caused by hypoxia rather than hypercapnia of course.

Anything in moderation really.

[Nigel Hewitt]

I remember we used to strongly urge people not to over-hyperventilate before a snorkel dive as they could end up passing out at or near the surface after the snorkel dive.
This would be caused by hypoxia rather than hypercapnia of course.

I don't see the 'of course' there. That is just ordinary SWB.
The hyperventilation has just allowed them to stay there long enough it get into that territory. This looks like preventing tyre wear by restricting the petrol supply.

Your example of exhaling swimming seems to imply you can run on the oxygen in your blood longer if you can keep the CO2 tension down (yes I know it circulates as an acid combination with water but it acts the same way). Actually how exhaling helps isn't immediately clear to me. Will the CO2 level fall? or are you doing something like the freediver's 'swallow' (your body won't make you breath while you are swallowing as it 'knows' you will choke) to inhibit the breathing reflex for a moment by kidding your system that you aren't really holding you breath.

[Andy Wade]

:=I remember we used to strongly urge people not to over-hyperventilate before a snorkel dive as they could end up passing out at or near the surface after the snorkel dive.
:=This would be caused by hypoxia rather than hypercapnia of course.

I don't see the 'of course' there. That is just ordinary SWB.
The hyperventilation has just allowed them to stay there long enough it get into that territory. This looks like preventing tyre wear by restricting the petrol supply.

Your example of exhaling swimming seems to imply you can run on the oxygen in your blood longer if you can keep the CO2 tension down (yes I know it circulates as an acid combination with water but it acts the same way). Actually how exhaling helps isn't immediately clear to me.

Well it isn't really immediately clear to me either, I don't do any swallowing, I can however swim underwater further by whistling out instead of holding my breath.
Go figure.
If you say it's not Hypoxia that causes a blackout then I'm not really arguing that point, it's just what came first to mind.

Will the CO2 level fall? or are you doing something like the freediver's 'swallow' (your body won't make you breath while you are swallowing as it 'knows' you will choke) to inhibit the breathing reflex for a moment by kidding your system that you aren't really holding you breath.

[Allan J Bretherton]

:=
:=:=I remember we used to strongly urge people not to over-hyperventilate before a snorkel dive as they could end up passing out at or near the surface after the snorkel dive.
:=:=This would be caused by hypoxia rather than hypercapnia of course.
:=
:=I don't see the 'of course' there. That is just ordinary SWB.
:=The hyperventilation has just allowed them to stay there long enough it get into that territory. This looks like preventing tyre wear by restricting the petrol supply.
:=
:=Your example of exhaling swimming seems to imply you can run on the oxygen in your blood longer if you can keep the CO2 tension down (yes I know it circulates as an acid combination with water but it acts the same way). Actually how exhaling helps isn't immediately clear to me.

Well it isn't really immediately clear to me either, I don't do any swallowing, I can however swim underwater further by whistling out instead of holding my breath.
Go figure.
If you say it's not Hypoxia that causes a blackout then I'm not really arguing that point, it's just what came first to mind.

:=Will the CO2 level fall? or are you doing something like the freediver's 'swallow' (your body won't make you breath while you are swallowing as it 'knows' you will choke) to inhibit the breathing reflex for a moment by kidding your system that you aren't really holding you breath.

When do you realise that you?re out of air? When you?ve finished breathing out and try to breath in again so the question is really superfluous isn?t it?

[janos]

I should start by saying that my original response was perhaps inadequately phrased - CO2 blackout certainly can occur, though the mechanism is not quite as you describe.

Probably not quite as I describe - it's hard to do in writing - I need pictures really. Or at least be able to wave my hands around, which is again hard to do online. Actually it's impossible to explain science if you can't wave your hands around.

Anyway The mechanism as I understood it was problems with CO2 reaching the bloodstream => no oxy-haemoglobin breakdown, then 1st bit of CO2 causes very rapid breakdown of lots of Oxy-haemoglobin => Lots of O2 => loss of function as in narcosis

My current boss explained it to me, and he was involved in some of the original research into this and narcosis (involved him sitting in a bath of 5 degree water at the SETT).

A. Angel (can't remember what the first initial stands for) has written a few good papers. Have a look. Even though they won't have any hand waving there might be diagrams.

HTH

Janos

PS - Definitely a bit of a digression from the original thread, but to bring it slightly back on track I once did feel a bit faint when I overdid it and swam through one too many hoops underwater.

[matts]

When do you realise that you?re out of air?

When the regulator goes tight.

When you?ve finished breathing out and try to breath in again so the question is really superfluous isn?t it?

Possibly not.

Hopefully it will have inspired a few to get in the pool and start experimenting with a snorkel.

[Allan J Bretherton]

:=When do you realise that you?re out of air?

When the regulator goes tight.

:=When you?ve finished breathing out and try to breath in again so the question is really superfluous isn?t it?

Possibly not.

Hopefully it will have inspired a few to get in the pool and start experimenting with a snorkel.

You could also check your gauge from time to time

[matts]

You could also check your gauge from time to time

And that of your buddy I would hope.

[Allan J Bretherton]

:=You could also check your gauge from time to time

And that of your buddy I would hope.

So would I Matt

[Philip Smith]

Actually it's impossible to explain science if you can't wave your hands around.

Tell that to Stephen Hawking!

P.