Residual Volume of lungs and OOA

Eddie wrote:
> and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were.

If you keep the air in your lungs during an ascent you will not be worried
about O2. There is no 'designed in' over pressure valve in your lungs and
holding your breath will probably kill you.

Lung over expansion injuries are probably a more messy way to die than
putting up with the discomfort of not breathing.

Conversely look at freedivers. The most dangerous part of a freedive is
the last 10m of the ascent where the expanding gas in the lungs has
exactly the opposite effect as the oxygen partial pressure drops.

Sorry. This is a non-starter. Blow bubbles all the way to the surface
just like they teach in every agencies diving 101.

nigelH

Eddie wrote:
> and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were.

If you keep the air in your lungs during an ascent you will not be worried
about O2. There is no 'designed in' over pressure valve in your lungs and
holding your breath will probably kill you.

Lung over expansion injuries are probably a more messy way to die than
putting up with the discomfort of not breathing.

Conversely look at freedivers. The most dangerous part of a freedive is
the last 10m of the ascent where the expanding gas in the lungs has
exactly the opposite effect as the oxygen partial pressure drops.

Sorry. This is a non-starter. Blow bubbles all the way to the surface
just like they teach in every agencies diving 101.

nigelH

Eddie wrote:
> and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were.

If you keep the air in your lungs during an ascent you will not be worried
about O2. There is no 'designed in' over pressure valve in your lungs and
holding your breath will probably kill you.

Lung over expansion injuries are probably a more messy way to die than
putting up with the discomfort of not breathing.

Conversely look at freedivers. The most dangerous part of a freedive is
the last 10m of the ascent where the expanding gas in the lungs has
exactly the opposite effect as the oxygen partial pressure drops.

Sorry. This is a non-starter. Blow bubbles all the way to the surface
just like they teach in every agencies diving 101.

nigelH

Eddie wrote:
> and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were.

If you keep the air in your lungs during an ascent you will not be worried
about O2. There is no 'designed in' over pressure valve in your lungs and
holding your breath will probably kill you.

Lung over expansion injuries are probably a more messy way to die than
putting up with the discomfort of not breathing.

Conversely look at freedivers. The most dangerous part of a freedive is
the last 10m of the ascent where the expanding gas in the lungs has
exactly the opposite effect as the oxygen partial pressure drops.

Sorry. This is a non-starter. Blow bubbles all the way to the surface
just like they teach in every agencies diving 101.

nigelH

Eddie wrote:
> and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were.

If you keep the air in your lungs during an ascent you will not be worried
about O2. There is no 'designed in' over pressure valve in your lungs and
holding your breath will probably kill you.

Lung over expansion injuries are probably a more messy way to die than
putting up with the discomfort of not breathing.

Conversely look at freedivers. The most dangerous part of a freedive is
the last 10m of the ascent where the expanding gas in the lungs has
exactly the opposite effect as the oxygen partial pressure drops.

Sorry. This is a non-starter. Blow bubbles all the way to the surface
just like they teach in every agencies diving 101.

nigelH

Eddie wrote:
> and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were.

If you keep the air in your lungs during an ascent you will not be worried
about O2. There is no 'designed in' over pressure valve in your lungs and
holding your breath will probably kill you.

Lung over expansion injuries are probably a more messy way to die than
putting up with the discomfort of not breathing.

Conversely look at freedivers. The most dangerous part of a freedive is
the last 10m of the ascent where the expanding gas in the lungs has
exactly the opposite effect as the oxygen partial pressure drops.

Sorry. This is a non-starter. Blow bubbles all the way to the surface
just like they teach in every agencies diving 101.

nigelH

Eddie wrote:
> and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were.

If you keep the air in your lungs during an ascent you will not be worried
about O2. There is no 'designed in' over pressure valve in your lungs and
holding your breath will probably kill you.

Lung over expansion injuries are probably a more messy way to die than
putting up with the discomfort of not breathing.

Conversely look at freedivers. The most dangerous part of a freedive is
the last 10m of the ascent where the expanding gas in the lungs has
exactly the opposite effect as the oxygen partial pressure drops.

Sorry. This is a non-starter. Blow bubbles all the way to the surface
just like they teach in every agencies diving 101.

nigelH

Eddie wrote:
> and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were.

If you keep the air in your lungs during an ascent you will not be worried
about O2. There is no 'designed in' over pressure valve in your lungs and
holding your breath will probably kill you.

Lung over expansion injuries are probably a more messy way to die than
putting up with the discomfort of not breathing.

Conversely look at freedivers. The most dangerous part of a freedive is
the last 10m of the ascent where the expanding gas in the lungs has
exactly the opposite effect as the oxygen partial pressure drops.

Sorry. This is a non-starter. Blow bubbles all the way to the surface
just like they teach in every agencies diving 101.

nigelH

"Eddie" <eddiej@gmail.com> wrote in message
news:1174855982.380356.298620@l77g2000hsb.googlegr oups.com...
> Hi guys,
> I have a query that I thought someone here may be able to help me
> with. I was in a conversation about lung capacities etc, and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were. I
> would have thought that this wouldn't happen, as the PO2 in the lungs
> would decrease on the ascent and perhaps the reverse would happen
> (i.e. some of the bloods O2 would diffuse into the lungs, further
> lowering the PO2 in the blood). What would be more likely?

First, in such an ascent you must NEVER hold your breath and in fact breathe
out continuously. As you ascend the volume of gas in your lungs would
increase so as to pressure-equilibrate with the water surrounding you, which
pressure is decreasing all the time. Hold your breath and the pressure in
your lungs may well cause an alveolar rupture which would give to a
pneumothorax or a gas embolus. Neither is pretty, both are capable of
killing you.

As you ascend (and take the example of breathing air at 30m) your PiO2
(press. of inspired oxygen) in your lungs would fall from 84kPa (4ATA at
30m) to 21kPa (1ATA at surface, 0m). (Actually they'd be a bit less than
this becuase of dilution with nitrogen in your residual lung volume, but
this will do for this argument.) There is then no question then of more
oxygen diffusing into the circulation as you ascend. However, when breathing
21kPa O2 (as we are when sitting at our PCs) we are able to saturate the
haemoglobin in the blood to its maximum capacity, and having higher inhaled
oxygen concentrations does not add any more to this. What will happen of
course is that the amount of oxygen in solution in your blood will fall, but
that part of the oxygen in our blood is a very small part of the total and
does not contribute significantly to the amount of oxygen our blood carries.

However as you ascend it is the case that there is sufficient oxygen in the
mass of gas in your lungs so that you need never become hypoxic during such
an ascent, so you need not fear for that.

Carbon dioxide is another matter. Your desire to breathe is far far more
significantly regulated by the partial pressure of CO2 in the blood than
that of oxygen in the blood. Normally you remove CO2 from the circulation by
venting it to the atmosphere with each breath. As you ascend, and as you
breathe out continuously, CO2 is also being vented continuously as you go so
the PaCO2 (pressure of CO2 in the arteries) is NOT NECESSARILY raised
either. I say not necessarily because frankly it all depends how well you
vent. Under-vent and it builds up a bit.

So, you should arrive at the surface in a (gas pressure terms) fit state. Of
course you will probably experience a certain amount of shortness of breath,
as likely to be brought about by anxiety / fear / panic rather than any
alteration of your blood gas profile. There is also the question of the
strech receptors within the lungs that frankly like to be kept moving. As
you vent and maintain a farily constant lung volume so your lungs do not
expand and contract during such an ascent. These receptors fire off,
reminding you to breathe. You can see their effect by your PC. Take a breath
(NOT a full lung capacity!) and hold it. Just as you get the desire to
breathe, while neither breathing in nor out, move your chest wall AS IF
breathing - you'll find you can buy yourself a few more seconds of breath
hold.

Hope this helps.

Ken

"Eddie" <eddiej@gmail.com> wrote in message
news:1174855982.380356.298620@l77g2000hsb.googlegr oups.com...
> Hi guys,
> I have a query that I thought someone here may be able to help me
> with. I was in a conversation about lung capacities etc, and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were. I
> would have thought that this wouldn't happen, as the PO2 in the lungs
> would decrease on the ascent and perhaps the reverse would happen
> (i.e. some of the bloods O2 would diffuse into the lungs, further
> lowering the PO2 in the blood). What would be more likely?

First, in such an ascent you must NEVER hold your breath and in fact breathe
out continuously. As you ascend the volume of gas in your lungs would
increase so as to pressure-equilibrate with the water surrounding you, which
pressure is decreasing all the time. Hold your breath and the pressure in
your lungs may well cause an alveolar rupture which would give to a
pneumothorax or a gas embolus. Neither is pretty, both are capable of
killing you.

As you ascend (and take the example of breathing air at 30m) your PiO2
(press. of inspired oxygen) in your lungs would fall from 84kPa (4ATA at
30m) to 21kPa (1ATA at surface, 0m). (Actually they'd be a bit less than
this becuase of dilution with nitrogen in your residual lung volume, but
this will do for this argument.) There is then no question then of more
oxygen diffusing into the circulation as you ascend. However, when breathing
21kPa O2 (as we are when sitting at our PCs) we are able to saturate the
haemoglobin in the blood to its maximum capacity, and having higher inhaled
oxygen concentrations does not add any more to this. What will happen of
course is that the amount of oxygen in solution in your blood will fall, but
that part of the oxygen in our blood is a very small part of the total and
does not contribute significantly to the amount of oxygen our blood carries.

However as you ascend it is the case that there is sufficient oxygen in the
mass of gas in your lungs so that you need never become hypoxic during such
an ascent, so you need not fear for that.

Carbon dioxide is another matter. Your desire to breathe is far far more
significantly regulated by the partial pressure of CO2 in the blood than
that of oxygen in the blood. Normally you remove CO2 from the circulation by
venting it to the atmosphere with each breath. As you ascend, and as you
breathe out continuously, CO2 is also being vented continuously as you go so
the PaCO2 (pressure of CO2 in the arteries) is NOT NECESSARILY raised
either. I say not necessarily because frankly it all depends how well you
vent. Under-vent and it builds up a bit.

So, you should arrive at the surface in a (gas pressure terms) fit state. Of
course you will probably experience a certain amount of shortness of breath,
as likely to be brought about by anxiety / fear / panic rather than any
alteration of your blood gas profile. There is also the question of the
strech receptors within the lungs that frankly like to be kept moving. As
you vent and maintain a farily constant lung volume so your lungs do not
expand and contract during such an ascent. These receptors fire off,
reminding you to breathe. You can see their effect by your PC. Take a breath
(NOT a full lung capacity!) and hold it. Just as you get the desire to
breathe, while neither breathing in nor out, move your chest wall AS IF
breathing - you'll find you can buy yourself a few more seconds of breath
hold.

Hope this helps.

Ken