Residual Volume of lungs and OOA

"Nigel Hewitt" <nigelhewitt@REMOVEhotmail.co.uk> wrote in message
news:28qdnTFsFv5nwJbbRVnyggA@bt.com...
> Ken wrote:
>> "Nigel Hewitt" wrote in message

> Wooo. Haemoglobin only ever gas transfers with the plasma that
> surrounds it. As the ppO2 in the lungs drops as you ascent the
> gas transfer in the Alveoli may reverse and hence haemoglobin
> also under certain circumstances. There is no magic one way valve,
> just basic physics, at work here. Consider the Freediver's Samba.
> This always occurs shallow and I've been grabbed returning from a
> rather slow 22m dive where I remembered it right to the surface but
> was then told I sambered as I stated to breath down.

The association of oxygen with Hb and the dissociation of oxygen from Hb are
not exactly reversible processes at any PO2. The conditions in the lungs are
optimally set for association, and while dissociation can occur with a
sufficient pressure gradient under these conditions, the conditions are not
as favourable. At the point where the oxygen is required, in organs other
than the lungs, the conditions are set for dissociation. Lung tissue is so
fine that the cells which make up the alveoli don't need Hb for oxygen
delivery, they can get what O2 they need from the inhaled gas. Freediving is
a rather extreme example and yes it can and does happen here - but a diver
doing a rapid ascent is spending far less time apnoeic than a freediver who
has gone down and then meets this problem on the way up. Again, there are no
absolutes. of course it CAN happen, just not particularly likely to. Factors
which influence here are many and varied - what depth is the ascent
happening from? How rapidly is the ascent happening? What is the diver's
metabolic rate at this time? What gas mix was the diver breathing when
he/she experienced the OOA scenario? What's the diver's Hb concentration?
What state is the diver's circulatory system in? How big are the diver's
lugns relative to body mass? Did the diver begin the ascent at the end of a
normal exhalation, of a normal inhalation, or where in between? Does the
diver have any mucus plugs in the lung effectively isolating a number of
alveoli from normal ventilation?

The only thing we can ALL be agreed on I suspect is that as far as OOA
scenarios go, you are far far better off NOT encountering one in the first
place (keep an eye on consumption, keep equip in good working order etc).
Should you be so unfortunate as to need to do a rapid ascent, do so with an
open airway (the method of ensuring this is less important than the fact
that the airway is open) and let not haste be your killer - you can ascend
more slowly in an OOA situation from 3m than you can from 30m. Don't dive if
you have any respiratory problem that may cause air trapping, and there is
no absolutely 100% safe way of getting to the surface Polaris-style.

Ken

"Nigel Hewitt" <nigelhewitt@REMOVEhotmail.co.uk> wrote in message
news:28qdnTFsFv5nwJbbRVnyggA@bt.com...
> Ken wrote:
>> "Nigel Hewitt" wrote in message

> Wooo. Haemoglobin only ever gas transfers with the plasma that
> surrounds it. As the ppO2 in the lungs drops as you ascent the
> gas transfer in the Alveoli may reverse and hence haemoglobin
> also under certain circumstances. There is no magic one way valve,
> just basic physics, at work here. Consider the Freediver's Samba.
> This always occurs shallow and I've been grabbed returning from a
> rather slow 22m dive where I remembered it right to the surface but
> was then told I sambered as I stated to breath down.

The association of oxygen with Hb and the dissociation of oxygen from Hb are
not exactly reversible processes at any PO2. The conditions in the lungs are
optimally set for association, and while dissociation can occur with a
sufficient pressure gradient under these conditions, the conditions are not
as favourable. At the point where the oxygen is required, in organs other
than the lungs, the conditions are set for dissociation. Lung tissue is so
fine that the cells which make up the alveoli don't need Hb for oxygen
delivery, they can get what O2 they need from the inhaled gas. Freediving is
a rather extreme example and yes it can and does happen here - but a diver
doing a rapid ascent is spending far less time apnoeic than a freediver who
has gone down and then meets this problem on the way up. Again, there are no
absolutes. of course it CAN happen, just not particularly likely to. Factors
which influence here are many and varied - what depth is the ascent
happening from? How rapidly is the ascent happening? What is the diver's
metabolic rate at this time? What gas mix was the diver breathing when
he/she experienced the OOA scenario? What's the diver's Hb concentration?
What state is the diver's circulatory system in? How big are the diver's
lugns relative to body mass? Did the diver begin the ascent at the end of a
normal exhalation, of a normal inhalation, or where in between? Does the
diver have any mucus plugs in the lung effectively isolating a number of
alveoli from normal ventilation?

The only thing we can ALL be agreed on I suspect is that as far as OOA
scenarios go, you are far far better off NOT encountering one in the first
place (keep an eye on consumption, keep equip in good working order etc).
Should you be so unfortunate as to need to do a rapid ascent, do so with an
open airway (the method of ensuring this is less important than the fact
that the airway is open) and let not haste be your killer - you can ascend
more slowly in an OOA situation from 3m than you can from 30m. Don't dive if
you have any respiratory problem that may cause air trapping, and there is
no absolutely 100% safe way of getting to the surface Polaris-style.

Ken

Ken wrote:
> "Nigel Hewitt" wrote in message

>> I'm not sure lungs work like that. Even 'fully' exhaled the alveoli
>> don't flatten out so what 'a quarter full' might represent is
>> dubious. A full breath at the surface does not leave me enough
>> volume to even let me clear my ears with a normal scuba mask
>> freediving to 30meters.
>
> Exactly my point in my discussion with Lee Bell. What do you mean by
> 1/4 full given that they never empty, and 1/4 full from what point of
> reference?

I think you'll find Lee is deliberately vague on that point. He is not
doing maths and he has done it in the water which counts for more
than our armchair diving. I agree with him that an open airway is enough
but it took me a long time to learn to consciously control the valve
in my head that switches neither/mouth/nose/both and I'd hate
my life to hang on it. Moving gas, I hum rather than the PADI
'blow bubbles', makes it much more sure to be open.

>> don't think you will gain anything O2 wize by holding a breath on
>> the ascent as the O2 has already been taken when the ppO2 was high
>> and as it falls your lungs might actually take oxygen back from your
>> blood.
>
> While diffusion back from the blood to the lungs is a reality, it is a
> reality of no importance. The haemoglobin dissociation curve is such
> that no desaturation of haemoglobin will occur, and the only oxygen
> that will diffuse back from the blood into the gas spaces of the
> lungs is that oxygen which is in solution in the plasma.

Wooo. Haemoglobin only ever gas transfers with the plasma that
surrounds it. As the ppO2 in the lungs drops as you ascent the
gas transfer in the Alveoli may reverse and hence haemoglobin
also under certain circumstances. There is no magic one way valve,
just basic physics, at work here. Consider the Freediver's Samba.
This always occurs shallow and I've been grabbed returning from a
rather slow 22m dive where I remembered it right to the surface but
was then told I sambered as I stated to breath down.

nigelH

"Nigel Hewitt" <nigelhewitt@hotmail.co.uk> wrote in message
news:460a31d2$0$16341$88260bb3@free.teranews.com.. .
> Doh <Doh@microsoft.com> wrote:
>
>> Ye, but the arguement was if he only started with (in this case) a half
>> lungs full, he would be ok if he didn't breathe out at all.
>> (Half lungs at ten metres becomes a lung full at 0M)
>
> I'm not sure lungs work like that. Even 'fully' exhaled the alveoli don't
> flatten out so what 'a quarter full' might represent is dubious. A full
> breath at the surface does not leave me enough volume to even let me
> clear my ears with a normal scuba mask freediving to 30meters.
>
> The big danger is there is nothing in our evolutionary environment that
> could provide lung over pressure so we have no built in protection
> against it. You can hold your breath against a pressure that will kill
> you. If we had an over-pressure valve built in I'd say hang onto
> everything you've got but as drowning in my own blood is not a prospect
> I relish I will exhale on any ascent that involved breathing compressed
> air at depth. Actually you have been breathing raised O2 levels (air at
> 10m = 0.42bar) so you can go a little bit longer and there are tricks
> to stave off the discomfort from CO2. I don't think you will gain anything
> O2 wize by holding a breath on the ascent as the O2 has already been taken
> when the ppO2 was high and as it falls your lungs might actually take
> oxygen back from your blood.

People are usually deaf to the concept (in fact I was excommunicated from
Scubaboard for advocating it).

If you practice breathing the LPI on your wing, you can exercise the need
for your lungs to cycle (CO2 discomfort), rebreathe mix you're wasting and
only using around 15% of, per lung cycle.

It works great, and relieves a lot of the anxiety of an ESA that comes
from lung discomfort.

"Nigel Hewitt" <nigelhewitt@REMOVEhotmail.co.uk> wrote in message
news:28qdnTFsFv5nwJbbRVnyggA@bt.com...
> Ken wrote:
>> "Nigel Hewitt" wrote in message

> Wooo. Haemoglobin only ever gas transfers with the plasma that
> surrounds it. As the ppO2 in the lungs drops as you ascent the
> gas transfer in the Alveoli may reverse and hence haemoglobin
> also under certain circumstances. There is no magic one way valve,
> just basic physics, at work here. Consider the Freediver's Samba.
> This always occurs shallow and I've been grabbed returning from a
> rather slow 22m dive where I remembered it right to the surface but
> was then told I sambered as I stated to breath down.

The association of oxygen with Hb and the dissociation of oxygen from Hb are
not exactly reversible processes at any PO2. The conditions in the lungs are
optimally set for association, and while dissociation can occur with a
sufficient pressure gradient under these conditions, the conditions are not
as favourable. At the point where the oxygen is required, in organs other
than the lungs, the conditions are set for dissociation. Lung tissue is so
fine that the cells which make up the alveoli don't need Hb for oxygen
delivery, they can get what O2 they need from the inhaled gas. Freediving is
a rather extreme example and yes it can and does happen here - but a diver
doing a rapid ascent is spending far less time apnoeic than a freediver who
has gone down and then meets this problem on the way up. Again, there are no
absolutes. of course it CAN happen, just not particularly likely to. Factors
which influence here are many and varied - what depth is the ascent
happening from? How rapidly is the ascent happening? What is the diver's
metabolic rate at this time? What gas mix was the diver breathing when
he/she experienced the OOA scenario? What's the diver's Hb concentration?
What state is the diver's circulatory system in? How big are the diver's
lugns relative to body mass? Did the diver begin the ascent at the end of a
normal exhalation, of a normal inhalation, or where in between? Does the
diver have any mucus plugs in the lung effectively isolating a number of
alveoli from normal ventilation?

The only thing we can ALL be agreed on I suspect is that as far as OOA
scenarios go, you are far far better off NOT encountering one in the first
place (keep an eye on consumption, keep equip in good working order etc).
Should you be so unfortunate as to need to do a rapid ascent, do so with an
open airway (the method of ensuring this is less important than the fact
that the airway is open) and let not haste be your killer - you can ascend
more slowly in an OOA situation from 3m than you can from 30m. Don't dive if
you have any respiratory problem that may cause air trapping, and there is
no absolutely 100% safe way of getting to the surface Polaris-style.

Ken