Residual Volume of lungs and OOA

Ken wrote

> 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) . . .

Good depth to discuss. Most divers find out they are OOA when they have
breathed out, not when they have a lung full of gas. Without getting into
the question of tidal flow and minimum percentage content of the lungs,
assume for a second that your lungs are only 1/4 full when you discover you
are out of gas at 30 meters. As you note, you are at a absolute pressure of
4 atmospheres. At the surface, the gas in your lungs will have expanded all
the way up to, you got it, one lung full of gas.

This is not suggesting it's a good idea to hold your breath while ascending.
It is only to point out that the degree of risk is not normally as severe as
taught. You should never ascend very far with the airways closed, but
breathing out is not the only way to keep them open. They're open when you
are inhaling too. As you ascend from our proposed 30 meters, the amount of
gas available from the tank benefits from the lowering of pressure. From
the 30 meter dive to the surface, you can actually get extra gas equal to 3
times the internal volume of your tanks. One ata stays in the tank. The
other two can be used. So figure out what the internal volume of your tanks
is, multiply it by 3 and divide it by whatever you figure the tidal volume
of your lungs is. That's how many additional breaths you get on your way to
the surface. Rather than exhale all the way, something you do only if you
have absolutely no other option, take advantage of the additional gas and
make a successful ascent a lot more likely.

> 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.

That is not something you can depend on. There are too many variables.
Shallow water blackout is caused by the combination of O2 used by the body
tissues and reduced pressure that combine to bring the PPO2 to less than .16
ATA, the level normally considered necessary to maintain consciousness.

Lee

Ken wrote

> 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) . . .

Good depth to discuss. Most divers find out they are OOA when they have
breathed out, not when they have a lung full of gas. Without getting into
the question of tidal flow and minimum percentage content of the lungs,
assume for a second that your lungs are only 1/4 full when you discover you
are out of gas at 30 meters. As you note, you are at a absolute pressure of
4 atmospheres. At the surface, the gas in your lungs will have expanded all
the way up to, you got it, one lung full of gas.

This is not suggesting it's a good idea to hold your breath while ascending.
It is only to point out that the degree of risk is not normally as severe as
taught. You should never ascend very far with the airways closed, but
breathing out is not the only way to keep them open. They're open when you
are inhaling too. As you ascend from our proposed 30 meters, the amount of
gas available from the tank benefits from the lowering of pressure. From
the 30 meter dive to the surface, you can actually get extra gas equal to 3
times the internal volume of your tanks. One ata stays in the tank. The
other two can be used. So figure out what the internal volume of your tanks
is, multiply it by 3 and divide it by whatever you figure the tidal volume
of your lungs is. That's how many additional breaths you get on your way to
the surface. Rather than exhale all the way, something you do only if you
have absolutely no other option, take advantage of the additional gas and
make a successful ascent a lot more likely.

> 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.

That is not something you can depend on. There are too many variables.
Shallow water blackout is caused by the combination of O2 used by the body
tissues and reduced pressure that combine to bring the PPO2 to less than .16
ATA, the level normally considered necessary to maintain consciousness.

Lee

"Lee Bell" <pleebell@bellsouth.net> wrote in message
news:RkGNh.10824$nV1.10788@bignews6.bellsouth.net. ..
> Ken wrote
>
>> 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) . . .
>
> Good depth to discuss. Most divers find out they are OOA when they have
> breathed out, not when they have a lung full of gas. Without getting into
> the question of tidal flow and minimum percentage content of the lungs,
> assume for a second that your lungs are only 1/4 full when you discover
> you are out of gas at 30 meters. As you note, you are at a absolute
> pressure of 4 atmospheres. At the surface, the gas in your lungs will
> have expanded all the way up to, you got it, one lung full of gas.

Like so many things, it depends. Sure you tend to find out you're out of air
when you try to breathe in and can't - so your lungs are at the end of a
normal exhalation. At which point, for an adult with a total lung capacity
you'll find your actual lung volume is around 3L. This is made up of what
you can still forcibly breathe out - your exhalatory reserve volume - plus a
certain volume which you CANNOT breathe out, your residual volume (both
these together make up your functional residual capacity).

If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you end
up with a 12l vol - twice your total lung volume. If you don't exhale AT
SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.




> This is not suggesting it's a good idea to hold your breath while
> ascending. It is only to point out that the degree of risk is not normally
> as severe as taught. You should never ascend very far with the airways
> closed, but breathing out is not the only way to keep them open. They're
> open when you are inhaling too. As you ascend from our proposed 30
> meters, the amount of gas available from the tank benefits from the
> lowering of pressure. From the 30 meter dive to the surface, you can
> actually get extra gas equal to 3 times the internal volume of your tanks.
> One ata stays in the tank. The other two can be used. So figure out what
> the internal volume of your tanks is, multiply it by 3 and divide it by
> whatever you figure the tidal volume of your lungs is.

Not really. Your equipment is already malfunctioning (assuming it's not your
lack of attention that has put you in this predicament). Note that a well
functioning first stage regulates to around 10ATA above ambient pressure, so
at 30m you will need around 14ATA in your cylinder to get a breath. Sure, as
you come to the surface your equipment will function with lower cylinder
pressures, as 10+ambient becomes a smaller number.



>> 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.
>
> That is not something you can depend on. There are too many variables.
> Shallow water blackout is caused by the combination of O2 used by the body
> tissues and reduced pressure that combine to bring the PPO2 to less than
> .16 ATA, the level normally considered necessary to maintain
> consciousness.

No, this too depends on your rate of oxygen consumption. Of course an option
no-one has discussed is using your alternate air source - and I don't mean
your second 2nd stage connected to the same empty cylinder! I mean using a
pony. I had a free flow at the bottom of Stoney a few years ago, and I made
a normal ascent which took me 8 mins from 32m thanks to my 3L cylinder.
There is also the option of a "spare air" bottle (he said ducking as
everyone throws blunt objects at me!), or one option which is rarely
discussed, breathing from the BCD.

If you do this, you can breathe in and out continuously as you ascend - but
not enough gas there to do a safety stop, just come up. The composition of
the gas there is the same as whatever your cylinder held. You breathe in and
out from the hose and yes, you do accumulate some CO2 BUT you'll have
probably made the surface BEFORE this becomes a real issue. As you are
breathing continuously, your airway is open. As you get nearer the surface,
you can exhale through your nose discarding some volume as the vol of the
BCD will have increased. You may have also dropped some weights, as getting
to the surface is a priority and positive buoyancy is not an issue.

Ken

"Lee Bell" <pleebell@bellsouth.net> wrote in message
news:RkGNh.10824$nV1.10788@bignews6.bellsouth.net. ..
> Ken wrote
>
>> 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) . . .
>
> Good depth to discuss. Most divers find out they are OOA when they have
> breathed out, not when they have a lung full of gas. Without getting into
> the question of tidal flow and minimum percentage content of the lungs,
> assume for a second that your lungs are only 1/4 full when you discover
> you are out of gas at 30 meters. As you note, you are at a absolute
> pressure of 4 atmospheres. At the surface, the gas in your lungs will
> have expanded all the way up to, you got it, one lung full of gas.

Like so many things, it depends. Sure you tend to find out you're out of air
when you try to breathe in and can't - so your lungs are at the end of a
normal exhalation. At which point, for an adult with a total lung capacity
you'll find your actual lung volume is around 3L. This is made up of what
you can still forcibly breathe out - your exhalatory reserve volume - plus a
certain volume which you CANNOT breathe out, your residual volume (both
these together make up your functional residual capacity).

If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you end
up with a 12l vol - twice your total lung volume. If you don't exhale AT
SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.




> This is not suggesting it's a good idea to hold your breath while
> ascending. It is only to point out that the degree of risk is not normally
> as severe as taught. You should never ascend very far with the airways
> closed, but breathing out is not the only way to keep them open. They're
> open when you are inhaling too. As you ascend from our proposed 30
> meters, the amount of gas available from the tank benefits from the
> lowering of pressure. From the 30 meter dive to the surface, you can
> actually get extra gas equal to 3 times the internal volume of your tanks.
> One ata stays in the tank. The other two can be used. So figure out what
> the internal volume of your tanks is, multiply it by 3 and divide it by
> whatever you figure the tidal volume of your lungs is.

Not really. Your equipment is already malfunctioning (assuming it's not your
lack of attention that has put you in this predicament). Note that a well
functioning first stage regulates to around 10ATA above ambient pressure, so
at 30m you will need around 14ATA in your cylinder to get a breath. Sure, as
you come to the surface your equipment will function with lower cylinder
pressures, as 10+ambient becomes a smaller number.



>> 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.
>
> That is not something you can depend on. There are too many variables.
> Shallow water blackout is caused by the combination of O2 used by the body
> tissues and reduced pressure that combine to bring the PPO2 to less than
> .16 ATA, the level normally considered necessary to maintain
> consciousness.

No, this too depends on your rate of oxygen consumption. Of course an option
no-one has discussed is using your alternate air source - and I don't mean
your second 2nd stage connected to the same empty cylinder! I mean using a
pony. I had a free flow at the bottom of Stoney a few years ago, and I made
a normal ascent which took me 8 mins from 32m thanks to my 3L cylinder.
There is also the option of a "spare air" bottle (he said ducking as
everyone throws blunt objects at me!), or one option which is rarely
discussed, breathing from the BCD.

If you do this, you can breathe in and out continuously as you ascend - but
not enough gas there to do a safety stop, just come up. The composition of
the gas there is the same as whatever your cylinder held. You breathe in and
out from the hose and yes, you do accumulate some CO2 BUT you'll have
probably made the surface BEFORE this becomes a real issue. As you are
breathing continuously, your airway is open. As you get nearer the surface,
you can exhale through your nose discarding some volume as the vol of the
BCD will have increased. You may have also dropped some weights, as getting
to the surface is a priority and positive buoyancy is not an issue.

Ken

"Lee Bell" <pleebell@bellsouth.net> wrote in message
news:RkGNh.10824$nV1.10788@bignews6.bellsouth.net. ..
> Ken wrote
>
>> 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) . . .
>
> Good depth to discuss. Most divers find out they are OOA when they have
> breathed out, not when they have a lung full of gas. Without getting into
> the question of tidal flow and minimum percentage content of the lungs,
> assume for a second that your lungs are only 1/4 full when you discover
> you are out of gas at 30 meters. As you note, you are at a absolute
> pressure of 4 atmospheres. At the surface, the gas in your lungs will
> have expanded all the way up to, you got it, one lung full of gas.

Like so many things, it depends. Sure you tend to find out you're out of air
when you try to breathe in and can't - so your lungs are at the end of a
normal exhalation. At which point, for an adult with a total lung capacity
you'll find your actual lung volume is around 3L. This is made up of what
you can still forcibly breathe out - your exhalatory reserve volume - plus a
certain volume which you CANNOT breathe out, your residual volume (both
these together make up your functional residual capacity).

If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you end
up with a 12l vol - twice your total lung volume. If you don't exhale AT
SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.




> This is not suggesting it's a good idea to hold your breath while
> ascending. It is only to point out that the degree of risk is not normally
> as severe as taught. You should never ascend very far with the airways
> closed, but breathing out is not the only way to keep them open. They're
> open when you are inhaling too. As you ascend from our proposed 30
> meters, the amount of gas available from the tank benefits from the
> lowering of pressure. From the 30 meter dive to the surface, you can
> actually get extra gas equal to 3 times the internal volume of your tanks.
> One ata stays in the tank. The other two can be used. So figure out what
> the internal volume of your tanks is, multiply it by 3 and divide it by
> whatever you figure the tidal volume of your lungs is.

Not really. Your equipment is already malfunctioning (assuming it's not your
lack of attention that has put you in this predicament). Note that a well
functioning first stage regulates to around 10ATA above ambient pressure, so
at 30m you will need around 14ATA in your cylinder to get a breath. Sure, as
you come to the surface your equipment will function with lower cylinder
pressures, as 10+ambient becomes a smaller number.



>> 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.
>
> That is not something you can depend on. There are too many variables.
> Shallow water blackout is caused by the combination of O2 used by the body
> tissues and reduced pressure that combine to bring the PPO2 to less than
> .16 ATA, the level normally considered necessary to maintain
> consciousness.

No, this too depends on your rate of oxygen consumption. Of course an option
no-one has discussed is using your alternate air source - and I don't mean
your second 2nd stage connected to the same empty cylinder! I mean using a
pony. I had a free flow at the bottom of Stoney a few years ago, and I made
a normal ascent which took me 8 mins from 32m thanks to my 3L cylinder.
There is also the option of a "spare air" bottle (he said ducking as
everyone throws blunt objects at me!), or one option which is rarely
discussed, breathing from the BCD.

If you do this, you can breathe in and out continuously as you ascend - but
not enough gas there to do a safety stop, just come up. The composition of
the gas there is the same as whatever your cylinder held. You breathe in and
out from the hose and yes, you do accumulate some CO2 BUT you'll have
probably made the surface BEFORE this becomes a real issue. As you are
breathing continuously, your airway is open. As you get nearer the surface,
you can exhale through your nose discarding some volume as the vol of the
BCD will have increased. You may have also dropped some weights, as getting
to the surface is a priority and positive buoyancy is not an issue.

Ken

"Lee Bell" <pleebell@bellsouth.net> wrote in message
news:RkGNh.10824$nV1.10788@bignews6.bellsouth.net. ..
> Ken wrote
>
>> 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) . . .
>
> Good depth to discuss. Most divers find out they are OOA when they have
> breathed out, not when they have a lung full of gas. Without getting into
> the question of tidal flow and minimum percentage content of the lungs,
> assume for a second that your lungs are only 1/4 full when you discover
> you are out of gas at 30 meters. As you note, you are at a absolute
> pressure of 4 atmospheres. At the surface, the gas in your lungs will
> have expanded all the way up to, you got it, one lung full of gas.

Like so many things, it depends. Sure you tend to find out you're out of air
when you try to breathe in and can't - so your lungs are at the end of a
normal exhalation. At which point, for an adult with a total lung capacity
you'll find your actual lung volume is around 3L. This is made up of what
you can still forcibly breathe out - your exhalatory reserve volume - plus a
certain volume which you CANNOT breathe out, your residual volume (both
these together make up your functional residual capacity).

If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you end
up with a 12l vol - twice your total lung volume. If you don't exhale AT
SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.




> This is not suggesting it's a good idea to hold your breath while
> ascending. It is only to point out that the degree of risk is not normally
> as severe as taught. You should never ascend very far with the airways
> closed, but breathing out is not the only way to keep them open. They're
> open when you are inhaling too. As you ascend from our proposed 30
> meters, the amount of gas available from the tank benefits from the
> lowering of pressure. From the 30 meter dive to the surface, you can
> actually get extra gas equal to 3 times the internal volume of your tanks.
> One ata stays in the tank. The other two can be used. So figure out what
> the internal volume of your tanks is, multiply it by 3 and divide it by
> whatever you figure the tidal volume of your lungs is.

Not really. Your equipment is already malfunctioning (assuming it's not your
lack of attention that has put you in this predicament). Note that a well
functioning first stage regulates to around 10ATA above ambient pressure, so
at 30m you will need around 14ATA in your cylinder to get a breath. Sure, as
you come to the surface your equipment will function with lower cylinder
pressures, as 10+ambient becomes a smaller number.



>> 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.
>
> That is not something you can depend on. There are too many variables.
> Shallow water blackout is caused by the combination of O2 used by the body
> tissues and reduced pressure that combine to bring the PPO2 to less than
> .16 ATA, the level normally considered necessary to maintain
> consciousness.

No, this too depends on your rate of oxygen consumption. Of course an option
no-one has discussed is using your alternate air source - and I don't mean
your second 2nd stage connected to the same empty cylinder! I mean using a
pony. I had a free flow at the bottom of Stoney a few years ago, and I made
a normal ascent which took me 8 mins from 32m thanks to my 3L cylinder.
There is also the option of a "spare air" bottle (he said ducking as
everyone throws blunt objects at me!), or one option which is rarely
discussed, breathing from the BCD.

If you do this, you can breathe in and out continuously as you ascend - but
not enough gas there to do a safety stop, just come up. The composition of
the gas there is the same as whatever your cylinder held. You breathe in and
out from the hose and yes, you do accumulate some CO2 BUT you'll have
probably made the surface BEFORE this becomes a real issue. As you are
breathing continuously, your airway is open. As you get nearer the surface,
you can exhale through your nose discarding some volume as the vol of the
BCD will have increased. You may have also dropped some weights, as getting
to the surface is a priority and positive buoyancy is not an issue.

Ken

"Lee Bell" <pleebell@bellsouth.net> wrote in message
news:RkGNh.10824$nV1.10788@bignews6.bellsouth.net. ..
> Ken wrote
>
>> 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) . . .
>
> Good depth to discuss. Most divers find out they are OOA when they have
> breathed out, not when they have a lung full of gas. Without getting into
> the question of tidal flow and minimum percentage content of the lungs,
> assume for a second that your lungs are only 1/4 full when you discover
> you are out of gas at 30 meters. As you note, you are at a absolute
> pressure of 4 atmospheres. At the surface, the gas in your lungs will
> have expanded all the way up to, you got it, one lung full of gas.

Like so many things, it depends. Sure you tend to find out you're out of air
when you try to breathe in and can't - so your lungs are at the end of a
normal exhalation. At which point, for an adult with a total lung capacity
you'll find your actual lung volume is around 3L. This is made up of what
you can still forcibly breathe out - your exhalatory reserve volume - plus a
certain volume which you CANNOT breathe out, your residual volume (both
these together make up your functional residual capacity).

If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you end
up with a 12l vol - twice your total lung volume. If you don't exhale AT
SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.




> This is not suggesting it's a good idea to hold your breath while
> ascending. It is only to point out that the degree of risk is not normally
> as severe as taught. You should never ascend very far with the airways
> closed, but breathing out is not the only way to keep them open. They're
> open when you are inhaling too. As you ascend from our proposed 30
> meters, the amount of gas available from the tank benefits from the
> lowering of pressure. From the 30 meter dive to the surface, you can
> actually get extra gas equal to 3 times the internal volume of your tanks.
> One ata stays in the tank. The other two can be used. So figure out what
> the internal volume of your tanks is, multiply it by 3 and divide it by
> whatever you figure the tidal volume of your lungs is.

Not really. Your equipment is already malfunctioning (assuming it's not your
lack of attention that has put you in this predicament). Note that a well
functioning first stage regulates to around 10ATA above ambient pressure, so
at 30m you will need around 14ATA in your cylinder to get a breath. Sure, as
you come to the surface your equipment will function with lower cylinder
pressures, as 10+ambient becomes a smaller number.



>> 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.
>
> That is not something you can depend on. There are too many variables.
> Shallow water blackout is caused by the combination of O2 used by the body
> tissues and reduced pressure that combine to bring the PPO2 to less than
> .16 ATA, the level normally considered necessary to maintain
> consciousness.

No, this too depends on your rate of oxygen consumption. Of course an option
no-one has discussed is using your alternate air source - and I don't mean
your second 2nd stage connected to the same empty cylinder! I mean using a
pony. I had a free flow at the bottom of Stoney a few years ago, and I made
a normal ascent which took me 8 mins from 32m thanks to my 3L cylinder.
There is also the option of a "spare air" bottle (he said ducking as
everyone throws blunt objects at me!), or one option which is rarely
discussed, breathing from the BCD.

If you do this, you can breathe in and out continuously as you ascend - but
not enough gas there to do a safety stop, just come up. The composition of
the gas there is the same as whatever your cylinder held. You breathe in and
out from the hose and yes, you do accumulate some CO2 BUT you'll have
probably made the surface BEFORE this becomes a real issue. As you are
breathing continuously, your airway is open. As you get nearer the surface,
you can exhale through your nose discarding some volume as the vol of the
BCD will have increased. You may have also dropped some weights, as getting
to the surface is a priority and positive buoyancy is not an issue.

Ken

"Lee Bell" <pleebell@bellsouth.net> wrote in message
news:RkGNh.10824$nV1.10788@bignews6.bellsouth.net. ..
> Ken wrote
>
>> 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) . . .
>
> Good depth to discuss. Most divers find out they are OOA when they have
> breathed out, not when they have a lung full of gas. Without getting into
> the question of tidal flow and minimum percentage content of the lungs,
> assume for a second that your lungs are only 1/4 full when you discover
> you are out of gas at 30 meters. As you note, you are at a absolute
> pressure of 4 atmospheres. At the surface, the gas in your lungs will
> have expanded all the way up to, you got it, one lung full of gas.

Like so many things, it depends. Sure you tend to find out you're out of air
when you try to breathe in and can't - so your lungs are at the end of a
normal exhalation. At which point, for an adult with a total lung capacity
you'll find your actual lung volume is around 3L. This is made up of what
you can still forcibly breathe out - your exhalatory reserve volume - plus a
certain volume which you CANNOT breathe out, your residual volume (both
these together make up your functional residual capacity).

If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you end
up with a 12l vol - twice your total lung volume. If you don't exhale AT
SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.




> This is not suggesting it's a good idea to hold your breath while
> ascending. It is only to point out that the degree of risk is not normally
> as severe as taught. You should never ascend very far with the airways
> closed, but breathing out is not the only way to keep them open. They're
> open when you are inhaling too. As you ascend from our proposed 30
> meters, the amount of gas available from the tank benefits from the
> lowering of pressure. From the 30 meter dive to the surface, you can
> actually get extra gas equal to 3 times the internal volume of your tanks.
> One ata stays in the tank. The other two can be used. So figure out what
> the internal volume of your tanks is, multiply it by 3 and divide it by
> whatever you figure the tidal volume of your lungs is.

Not really. Your equipment is already malfunctioning (assuming it's not your
lack of attention that has put you in this predicament). Note that a well
functioning first stage regulates to around 10ATA above ambient pressure, so
at 30m you will need around 14ATA in your cylinder to get a breath. Sure, as
you come to the surface your equipment will function with lower cylinder
pressures, as 10+ambient becomes a smaller number.



>> 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.
>
> That is not something you can depend on. There are too many variables.
> Shallow water blackout is caused by the combination of O2 used by the body
> tissues and reduced pressure that combine to bring the PPO2 to less than
> .16 ATA, the level normally considered necessary to maintain
> consciousness.

No, this too depends on your rate of oxygen consumption. Of course an option
no-one has discussed is using your alternate air source - and I don't mean
your second 2nd stage connected to the same empty cylinder! I mean using a
pony. I had a free flow at the bottom of Stoney a few years ago, and I made
a normal ascent which took me 8 mins from 32m thanks to my 3L cylinder.
There is also the option of a "spare air" bottle (he said ducking as
everyone throws blunt objects at me!), or one option which is rarely
discussed, breathing from the BCD.

If you do this, you can breathe in and out continuously as you ascend - but
not enough gas there to do a safety stop, just come up. The composition of
the gas there is the same as whatever your cylinder held. You breathe in and
out from the hose and yes, you do accumulate some CO2 BUT you'll have
probably made the surface BEFORE this becomes a real issue. As you are
breathing continuously, your airway is open. As you get nearer the surface,
you can exhale through your nose discarding some volume as the vol of the
BCD will have increased. You may have also dropped some weights, as getting
to the surface is a priority and positive buoyancy is not an issue.

Ken

"Lee Bell" <pleebell@bellsouth.net> wrote in message
news:RkGNh.10824$nV1.10788@bignews6.bellsouth.net. ..
> Ken wrote
>
>> 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) . . .
>
> Good depth to discuss. Most divers find out they are OOA when they have
> breathed out, not when they have a lung full of gas. Without getting into
> the question of tidal flow and minimum percentage content of the lungs,
> assume for a second that your lungs are only 1/4 full when you discover
> you are out of gas at 30 meters. As you note, you are at a absolute
> pressure of 4 atmospheres. At the surface, the gas in your lungs will
> have expanded all the way up to, you got it, one lung full of gas.

Like so many things, it depends. Sure you tend to find out you're out of air
when you try to breathe in and can't - so your lungs are at the end of a
normal exhalation. At which point, for an adult with a total lung capacity
you'll find your actual lung volume is around 3L. This is made up of what
you can still forcibly breathe out - your exhalatory reserve volume - plus a
certain volume which you CANNOT breathe out, your residual volume (both
these together make up your functional residual capacity).

If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you end
up with a 12l vol - twice your total lung volume. If you don't exhale AT
SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.




> This is not suggesting it's a good idea to hold your breath while
> ascending. It is only to point out that the degree of risk is not normally
> as severe as taught. You should never ascend very far with the airways
> closed, but breathing out is not the only way to keep them open. They're
> open when you are inhaling too. As you ascend from our proposed 30
> meters, the amount of gas available from the tank benefits from the
> lowering of pressure. From the 30 meter dive to the surface, you can
> actually get extra gas equal to 3 times the internal volume of your tanks.
> One ata stays in the tank. The other two can be used. So figure out what
> the internal volume of your tanks is, multiply it by 3 and divide it by
> whatever you figure the tidal volume of your lungs is.

Not really. Your equipment is already malfunctioning (assuming it's not your
lack of attention that has put you in this predicament). Note that a well
functioning first stage regulates to around 10ATA above ambient pressure, so
at 30m you will need around 14ATA in your cylinder to get a breath. Sure, as
you come to the surface your equipment will function with lower cylinder
pressures, as 10+ambient becomes a smaller number.



>> 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.
>
> That is not something you can depend on. There are too many variables.
> Shallow water blackout is caused by the combination of O2 used by the body
> tissues and reduced pressure that combine to bring the PPO2 to less than
> .16 ATA, the level normally considered necessary to maintain
> consciousness.

No, this too depends on your rate of oxygen consumption. Of course an option
no-one has discussed is using your alternate air source - and I don't mean
your second 2nd stage connected to the same empty cylinder! I mean using a
pony. I had a free flow at the bottom of Stoney a few years ago, and I made
a normal ascent which took me 8 mins from 32m thanks to my 3L cylinder.
There is also the option of a "spare air" bottle (he said ducking as
everyone throws blunt objects at me!), or one option which is rarely
discussed, breathing from the BCD.

If you do this, you can breathe in and out continuously as you ascend - but
not enough gas there to do a safety stop, just come up. The composition of
the gas there is the same as whatever your cylinder held. You breathe in and
out from the hose and yes, you do accumulate some CO2 BUT you'll have
probably made the surface BEFORE this becomes a real issue. As you are
breathing continuously, your airway is open. As you get nearer the surface,
you can exhale through your nose discarding some volume as the vol of the
BCD will have increased. You may have also dropped some weights, as getting
to the surface is a priority and positive buoyancy is not an issue.

Ken

"Lee Bell" <pleebell@bellsouth.net> wrote in message
news:RkGNh.10824$nV1.10788@bignews6.bellsouth.net. ..
> Ken wrote
>
>> 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) . . .
>
> Good depth to discuss. Most divers find out they are OOA when they have
> breathed out, not when they have a lung full of gas. Without getting into
> the question of tidal flow and minimum percentage content of the lungs,
> assume for a second that your lungs are only 1/4 full when you discover
> you are out of gas at 30 meters. As you note, you are at a absolute
> pressure of 4 atmospheres. At the surface, the gas in your lungs will
> have expanded all the way up to, you got it, one lung full of gas.

Like so many things, it depends. Sure you tend to find out you're out of air
when you try to breathe in and can't - so your lungs are at the end of a
normal exhalation. At which point, for an adult with a total lung capacity
you'll find your actual lung volume is around 3L. This is made up of what
you can still forcibly breathe out - your exhalatory reserve volume - plus a
certain volume which you CANNOT breathe out, your residual volume (both
these together make up your functional residual capacity).

If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you end
up with a 12l vol - twice your total lung volume. If you don't exhale AT
SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.




> This is not suggesting it's a good idea to hold your breath while
> ascending. It is only to point out that the degree of risk is not normally
> as severe as taught. You should never ascend very far with the airways
> closed, but breathing out is not the only way to keep them open. They're
> open when you are inhaling too. As you ascend from our proposed 30
> meters, the amount of gas available from the tank benefits from the
> lowering of pressure. From the 30 meter dive to the surface, you can
> actually get extra gas equal to 3 times the internal volume of your tanks.
> One ata stays in the tank. The other two can be used. So figure out what
> the internal volume of your tanks is, multiply it by 3 and divide it by
> whatever you figure the tidal volume of your lungs is.

Not really. Your equipment is already malfunctioning (assuming it's not your
lack of attention that has put you in this predicament). Note that a well
functioning first stage regulates to around 10ATA above ambient pressure, so
at 30m you will need around 14ATA in your cylinder to get a breath. Sure, as
you come to the surface your equipment will function with lower cylinder
pressures, as 10+ambient becomes a smaller number.



>> 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.
>
> That is not something you can depend on. There are too many variables.
> Shallow water blackout is caused by the combination of O2 used by the body
> tissues and reduced pressure that combine to bring the PPO2 to less than
> .16 ATA, the level normally considered necessary to maintain
> consciousness.

No, this too depends on your rate of oxygen consumption. Of course an option
no-one has discussed is using your alternate air source - and I don't mean
your second 2nd stage connected to the same empty cylinder! I mean using a
pony. I had a free flow at the bottom of Stoney a few years ago, and I made
a normal ascent which took me 8 mins from 32m thanks to my 3L cylinder.
There is also the option of a "spare air" bottle (he said ducking as
everyone throws blunt objects at me!), or one option which is rarely
discussed, breathing from the BCD.

If you do this, you can breathe in and out continuously as you ascend - but
not enough gas there to do a safety stop, just come up. The composition of
the gas there is the same as whatever your cylinder held. You breathe in and
out from the hose and yes, you do accumulate some CO2 BUT you'll have
probably made the surface BEFORE this becomes a real issue. As you are
breathing continuously, your airway is open. As you get nearer the surface,
you can exhale through your nose discarding some volume as the vol of the
BCD will have increased. You may have also dropped some weights, as getting
to the surface is a priority and positive buoyancy is not an issue.

Ken