syncope ??

paulraymaekers · 10th August 2007, 15:30

hello all, just a question that was raised yesterday during a course...

suppose, (just suppose!), you are on CCR, at 30ft (10 m) with a PPO2 of 0.21 for 10 minutes
you switch to OC (air) and ascent immediatly to surface
what could happen??

let's not look at possible decompression problem, but hypoxic problem!

will you faint when you arrive at surface or not?? (will the PPO2 in your brain be hypoxic??)

... just a question :-)

regards
paul

babar · 10th August 2007, 15:48

Quote: (Originally Posted by paulraymaekers)

hello all, just a question that was raised yesterday during a course...

suppose, (just suppose!), you are on CCR, at 30ft (10 m) with a PPO2 of 0.21 for 10 minutes
you switch to OC (air) and ascent immediatly to surface
what could happen??

let's not look at possible decompression problem, but hypoxic problem!

will you faint when you arrive at surface or not?? (will the PPO2 in your brain be hypoxic??)

... just a question :-)

regards
paul

Switch to OC and breath? or just ascend directly while exhaling? It's probobly an academic point, but as long as one keeps breathing an oxygen rich gas at depth it should not mater. A better question is WTF is he doing with a loop po2 of .21?

AD_ward9 · 10th August 2007, 15:49

Quote: (Originally Posted by paulraymaekers)

hello all, just a question that was raised yesterday during a course...

suppose, (just suppose!), you are on CCR, at 30ft (10 m) with a PPO2 of 0.21 for 10 minutes
you switch to OC (air) and ascent immediatly to surface
what could happen??

let's not look at possible decompression problem, but hypoxic problem!

will you faint when you arrive at surface or not?? (will the PPO2 in your brain be hypoxic??)

... just a question :-)

regards
paul

No, because in switching to air on O.C. you are putting a higher PPO2 into your lungs than in your blood (switching from a PPO2 of 0.21 to 0.4), therefore more O2 gets to your brain.

A no-brainer really.

Alex

**nigelh** · 10th August 2007, 15:51

Quote: (Originally Posted by paulraymaekers)

suppose, (just suppose!), you are on CCR, at 30ft (10 m) with a PPO2 of 0.21 for 10 minutes
you switch to OC (air) and ascent immediatly to surface
what could happen??

I thought there was a problem here once but have now realised that it's down to gas tensions (partial pressure in gas talk) and that means you have the same number of molecules of O2 in the tissues dependent on the ppO2 even though the fraction is low.

You can model each gas independently in physics.

Just like keeping 1.3bar ppO2 means I always have the same mass of O2 in the loop regardless of depth.

**rigdiver** · 10th August 2007, 16:07

Quote: (Originally Posted by paulraymaekers)

hello all, just a question that was raised yesterday during a course...

suppose, (just suppose!), you are on CCR, at 30ft (10 m) with a PPO2 of 0.21 for 10 minutes
you switch to OC (air) and ascent immediatly to surface
what could happen??

let's not look at possible decompression problem, but hypoxic problem!

will you faint when you arrive at surface or not?? (will the PPO2 in your brain be hypoxic??)

... just a question :-)

regards
paul

30ft to surface should be at least 1 minute. Surely there were a few breaths going up, so no you would not faint. If you held your breath then fainting would be the least of your problems.

paulraymaekers · 10th August 2007, 16:10

Quote: (Originally Posted by AD_ward9)

No, because in switching to air on O.C. you are putting a higher PPO2 into your lungs than in your blood (switching from a PPO2 of 0.21 to 0.4), therefore more O2 gets to your brain.

A no-brainer really.

Alex

euh, not what I ment..

more like: is the time of the blood-cycle longer than the ascent time

normally yes, so at surface your brain would still be at low PPO2 ..

paul

AD_ward9 · 10th August 2007, 16:11

Quote: (Originally Posted by babar)

Switch to OC and breath? or just ascend directly while exhaling? It's probobly an academic point, but as long as one keeps breathing an oxygen rich gas at depth it should not mater.

It does matter!

If you do not switch to O.C. and go for the surface, your PPO2 in your lungs just below the surface will be under 0.1. You will probably pass out and die.

This is NOT the same as ascending to the surface by exhaling from air O.C., where your PPO2 is always 0.21 minus a small amount for the O2 you consume during the last part of your ascent.

Instructors should reinforce that if your PPO2 is low, you MUST NOT ascend to the surface whether you are on the rebreather or not.

Alex

divetheworld · 10th August 2007, 16:14

Quote: (Originally Posted by AD_ward9)

It does matter!

If you do not switch to O.C. and go for the surface, your PPO2 in your lungs just below the surface will be under 0.1. You will probably pass out and die.

This is NOT the same as ascending to the surface by exhaling from air O.C., where your PPO2 is always 0.21 minus a small amount for the O2 you consume during the last part of your ascent.

Instructors should reinforce that if your PPO2 is low, you MUST NOT ascend to the surface whether you are on the rebreather or not.

Alex

I have to agree with Alex on both of his posts, and pray people take note of the quoted post abov.

Its what is in the lungs that matters, although I think Paul is wondering if, by his example, will their be enough oxygen at a cellular level to maintain conciousness upon an ascent.

AD_ward9 · 10th August 2007, 16:14

Quote: (Originally Posted by paulraymaekers)

euh, not what I ment..

more like: is the time of the blood-cycle longer than the ascent time

normally yes, so at surface your brain would still get low PPO2 blood..

paul

I have been involved in a fatal accident investigation where just this happened.

The diver was at 10m with a PPO2 of 0.45.

He swam rapidly to the surface on a rebreather, and did not make it.

O2 pours out of your blood into your lungs just as it pours from your lungs to your blood: osmosis. The blood in your lungs goes straight to your heart and that from your heart goes straight to your brain. Unless you can get to the surface in a couple of seconds, literally, you are dead if you try this. You die just below the surface when PPO2 is lowest.

Divers on rebreathers must keep this foremost. You cannot go to the surface if your PPO2 is low. You must increase the PPO2 or get ready to die.

Sorry to emphasise this, but it is alarming that the only other person on this thread who survives a bail out is Brent (divetheworld).

Alex

paulraymaekers · 10th August 2007, 16:30

Quote: (Originally Posted by AD_ward9)

I have been involved in a fatal accident investigation where just this happened.

The diver was at 10m with a PPO2 of 0.45.

He swam rapidly to the surface on a rebreather, and did not make it.

O2 pours out of your blood into your lungs just as it pours from your lungs to your blood: osmosis. The blood in your lungs goes straight to your heart and that from your heart goes straight to your brain. Unless you can get to the surface in a couple of seconds, literally, you are dead if you try this. You die just below the surface when PPO2 is lowest.

Divers on rebreathers must keep this foremost. You cannot go to the surface if your PPO2 is low. You must increase the PPO2 or get ready to die.

Sorry to emphasise this, but it is alarming that the only other person on this thread who survives a bail out is Brent (divetheworld).

Alex

hello Alex, this was not the question :-)

the scenario is: switch to OC air at 30ft, and ascent immediately to surface, before the blood has time to bring more oxigen to the brains, so the brain will still be at low PPO2 when the diver arrives at surface..

is it the PPO2 in the lungs or in the brain that matters??? I thought it was the brain??

regards
paul

10th August 2007, 15:30	#1 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,493	syncope ?? hello all, just a question that was raised yesterday during a course... suppose, (just suppose!), you are on CCR, at 30ft (10 m) with a PPO2 of 0.21 for 10 minutes you switch to OC (air) and ascent immediatly to surface what could happen?? let's not look at possible decompression problem, but hypoxic problem! will you faint when you arrive at surface or not?? (will the PPO2 in your brain be hypoxic??) ... just a question :-) regards paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...
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10th August 2007, 15:48	#2 (permalink)
babar Curmudgeon Current Rebreather/s: Evolution Sport Kiss Other CCR Other Rebreather/s: Inspiration Classic Inspiration Vision Evolution Other CCR Join Date: Apr 2005 Location: Southern California Posts: 417	Re: syncope ?? Quote: (Originally Posted by paulraymaekers) hello all, just a question that was raised yesterday during a course... suppose, (just suppose!), you are on CCR, at 30ft (10 m) with a PPO2 of 0.21 for 10 minutes you switch to OC (air) and ascent immediatly to surface what could happen?? let's not look at possible decompression problem, but hypoxic problem! will you faint when you arrive at surface or not?? (will the PPO2 in your brain be hypoxic??) ... just a question :-) regards paul Switch to OC and breath? or just ascend directly while exhaling? It's probobly an academic point, but as long as one keeps breathing an oxygen rich gas at depth it should not mater. A better question is WTF is he doing with a loop po2 of .21? __________________ Babar Evolution Plus Sport kiss
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10th August 2007, 15:49	#3 (permalink)
AD_ward9 So much more to learn Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 1,862	Re: syncope ?? Quote: (Originally Posted by paulraymaekers) hello all, just a question that was raised yesterday during a course... suppose, (just suppose!), you are on CCR, at 30ft (10 m) with a PPO2 of 0.21 for 10 minutes you switch to OC (air) and ascent immediatly to surface what could happen?? let's not look at possible decompression problem, but hypoxic problem! will you faint when you arrive at surface or not?? (will the PPO2 in your brain be hypoxic??) ... just a question :-) regards paul No, because in switching to air on O.C. you are putting a higher PPO2 into your lungs than in your blood (switching from a PPO2 of 0.21 to 0.4), therefore more O2 gets to your brain. A no-brainer really. Alex
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10th August 2007, 15:51	#4 (permalink)
nigelh New Member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 836	Re: syncope ?? Quote: (Originally Posted by paulraymaekers) suppose, (just suppose!), you are on CCR, at 30ft (10 m) with a PPO2 of 0.21 for 10 minutes you switch to OC (air) and ascent immediatly to surface what could happen?? I thought there was a problem here once but have now realised that it's down to gas tensions (partial pressure in gas talk) and that means you have the same number of molecules of O2 in the tissues dependent on the ppO2 even though the fraction is low. You can model each gas independently in physics. Just like keeping 1.3bar ppO2 means I always have the same mass of O2 in the loop regardless of depth. __________________ nigelh
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10th August 2007, 16:07	#5 (permalink)
rigdiver LEARNING CONTINUALLY Current Rebreather/s: Inspiration Vision Other Rebreather/s: Inspiration Classic Megalodon Join Date: Mar 2005 Location: TEXAS Posts: 410	Re: syncope ?? Quote: (Originally Posted by paulraymaekers) hello all, just a question that was raised yesterday during a course... suppose, (just suppose!), you are on CCR, at 30ft (10 m) with a PPO2 of 0.21 for 10 minutes you switch to OC (air) and ascent immediatly to surface what could happen?? let's not look at possible decompression problem, but hypoxic problem! will you faint when you arrive at surface or not?? (will the PPO2 in your brain be hypoxic??) ... just a question :-) regards paul 30ft to surface should be at least 1 minute. Surely there were a few breaths going up, so no you would not faint. If you held your breath then fainting would be the least of your problems.
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10th August 2007, 16:10	#6 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,493	Re: syncope ?? Quote: (Originally Posted by AD_ward9) No, because in switching to air on O.C. you are putting a higher PPO2 into your lungs than in your blood (switching from a PPO2 of 0.21 to 0.4), therefore more O2 gets to your brain. A no-brainer really. Alex euh, not what I ment.. more like: is the time of the blood-cycle longer than the ascent time normally yes, so at surface your brain would still be at low PPO2 .. paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...
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10th August 2007, 16:11	#7 (permalink)
AD_ward9 So much more to learn Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 1,862	Re: syncope ?? Quote: (Originally Posted by babar) Switch to OC and breath? or just ascend directly while exhaling? It's probobly an academic point, but as long as one keeps breathing an oxygen rich gas at depth it should not mater. It does matter! If you do not switch to O.C. and go for the surface, your PPO2 in your lungs just below the surface will be under 0.1. You will probably pass out and die. This is NOT the same as ascending to the surface by exhaling from air O.C., where your PPO2 is always 0.21 minus a small amount for the O2 you consume during the last part of your ascent. Instructors should reinforce that if your PPO2 is low, you MUST NOT ascend to the surface whether you are on the rebreather or not. Alex
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10th August 2007, 16:14	#8 (permalink)
divetheworld Dive porn pimp Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Classic Kiss Other CCR Join Date: Mar 2005 Location: Leeds, England Posts: 1,586	Re: syncope ?? Quote: (Originally Posted by AD_ward9) It does matter! If you do not switch to O.C. and go for the surface, your PPO2 in your lungs just below the surface will be under 0.1. You will probably pass out and die. This is NOT the same as ascending to the surface by exhaling from air O.C., where your PPO2 is always 0.21 minus a small amount for the O2 you consume during the last part of your ascent. Instructors should reinforce that if your PPO2 is low, you MUST NOT ascend to the surface whether you are on the rebreather or not. Alex I have to agree with Alex on both of his posts, and pray people take note of the quoted post abov. Its what is in the lungs that matters, although I think Paul is wondering if, by his example, will their be enough oxygen at a cellular level to maintain conciousness upon an ascent. __________________ Attitude and self praise is no reccomendation. Dont try to be a great man, just be a man and let history be the judge of you. CHECK OUT OUR INTERWEBS FOR CUSTOM REBREATHER UPGRADES *WWW.NARKEDAT90.CO.UK* *http://www.grpservices.com/pursuit/* Supporting Shearwater Research Products in Europe Last edited by divetheworld : 10th August 2007 at 16:16.
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10th August 2007, 16:14	#9 (permalink)
AD_ward9 So much more to learn Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 1,862	Re: syncope ?? Quote: (Originally Posted by paulraymaekers) euh, not what I ment.. more like: is the time of the blood-cycle longer than the ascent time normally yes, so at surface your brain would still get low PPO2 blood.. paul I have been involved in a fatal accident investigation where just this happened. The diver was at 10m with a PPO2 of 0.45. He swam rapidly to the surface on a rebreather, and did not make it. O2 pours out of your blood into your lungs just as it pours from your lungs to your blood: osmosis. The blood in your lungs goes straight to your heart and that from your heart goes straight to your brain. Unless you can get to the surface in a couple of seconds, literally, you are dead if you try this. You die just below the surface when PPO2 is lowest. Divers on rebreathers must keep this foremost. You cannot go to the surface if your PPO2 is low. You must increase the PPO2 or get ready to die. Sorry to emphasise this, but it is alarming that the only other person on this thread who survives a bail out is Brent (divetheworld). Alex Last edited by AD_ward9 : 10th August 2007 at 16:24.
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10th August 2007, 16:30	#10 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,493	Re: syncope ?? Quote: (Originally Posted by AD_ward9) I have been involved in a fatal accident investigation where just this happened. The diver was at 10m with a PPO2 of 0.45. He swam rapidly to the surface on a rebreather, and did not make it. O2 pours out of your blood into your lungs just as it pours from your lungs to your blood: osmosis. The blood in your lungs goes straight to your heart and that from your heart goes straight to your brain. Unless you can get to the surface in a couple of seconds, literally, you are dead if you try this. You die just below the surface when PPO2 is lowest. Divers on rebreathers must keep this foremost. You cannot go to the surface if your PPO2 is low. You must increase the PPO2 or get ready to die. Sorry to emphasise this, but it is alarming that the only other person on this thread who survives a bail out is Brent (divetheworld). Alex hello Alex, this was not the question :-) the scenario is: switch to OC air at 30ft, and ascent immediately to surface, before the blood has time to bring more oxigen to the brains, so the brain will still be at low PPO2 when the diver arrives at surface.. is it the PPO2 in the lungs or in the brain that matters??? I thought it was the brain?? regards paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...
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