C02 Retention / Decay times

Simon Mitchell · 1st November 2007, 20:25

Quote: (Originally Posted by womble)

The problem is, CO2 has a higher affinity to haemaglobin than O2, so you have to wait for all the CO2 to be flushed out of your system.

No, this is not the problem. The problem is that you are hypoventilating in relation to the CO2 you are producing (in retention), or that you are rebreathing CO2 (in scrubber failure).

Quote: (Originally Posted by womble)

Theoretically this would be better achieved by a higher PPo2, but there is also the increased risk of oxtox if breathing high PPO2 gas with significant CO2 retention . . . So is this an argument for carrying a not-very-hot deep bailout?? Say PPO2 1.5-1.6??

No its not. The last thing you want to do in the middle of a CO2 toxicity event is increase your PO2, even by a little. If anything, there might be an argument for a very light (helium-rich) bailout so that if you do bail in the middle of a CO2 (hit) the work of breathing is as low as you can possibly make it.

Regards,

Simon M

**Dsix36** · 1st November 2007, 20:31

Quote: (Originally Posted by womble)

Theoretically this would be better achieved by a higher PPo2, but there is also the increased risk of oxtox if breathing high PPO2 gas with significant CO2 retention . . . So is this an argument for carrying a not-very-hot deep bailout?? Say PPO2 1.5-1.6??

"not-very-hot" What do you consider hot?

I was trained to run a PPO2 of 1.2 under most normal circumstances and maybe bump it up for deco. 1.6 is absolute max.

womble · 1st November 2007, 20:48

Quote: (Originally Posted by Simon Mitchell)

No, this is not the problem. The problem is that you are hypoventilating in relation to the CO2 you are producing (in retention), or that you are rebreathing CO2 (in scrubber failure).

Yes you are hypoventilating, partly due to the psychological stress, but partly due to the higher levels of CO2 in your body. It is after all CO2 levels in the body that stimulates the breathing reflex. So as long as you have higher CO2 levels in your body, you will breathe heavier.

No its not. The last thing you want to do in the middle of a CO2 toxicity event is increase your PO2, even by a little.

Do you have any evidence to back this up?
So say you are diving a setpoint of 1.3, and your deep bailout has a PPO2 of 1.4-1.5 (Which is quite common practice) then what??

If anything, there might be an argument for a very light (helium-rich) bailout so that if you do bail in the middle of a CO2 (hit) the work of breathing is as low as you can possibly make it.

Regards,

Simon M

Quote: (Originally Posted by Dsix36)

"not-very-hot" What do you consider hot?

I was trained to run a PPO2 of 1.2 under most normal circumstances and maybe bump it up for deco. 1.6 is absolute max.

I would consider PPO2 greater than 1.7 hot. remember, I am talking about bailout here, not loop PPO2.

**Dsix36** · 1st November 2007, 20:54

Quote: (Originally Posted by womble)

I would consider PPO2 greater than 1.7 hot. remember, I am talking about bailout here, not loop PPO2.

Oops, I should read better

Mark Chase · 1st November 2007, 20:57

Quote: (Originally Posted by womble)

I would consider PPO2 greater than 1.7 hot. remember, I am talking about bailout here, not loop PPO2.

I generally avoid saying it in public but on an immediate ascent dive I often have a max tolerance on bailout of 2.0bar. On a return to shot is a must or overhead environment i keep it below 1.6.
_____

Some interesting stuff there Simon. I have always looked to instantly lower the helium content on bailout to reduce the deco commitment. So as an example, i dive 14/65 but have 18/45 for bailout.

Based on what your saying I should perhaps consider upping the helium content to reduce WOB as a priority over the additional deco.

ATB

Mark

**UWSojourner** · 1st November 2007, 21:02

Quote: (Originally Posted by womble)

I would consider PPO2 greater than 1.7 hot. remember, I am talking about bailout here, not loop PPO2.

I thought that elevated CO2 exposure increased susceptability to an O2 hit? If so, maybe hitting a hot mix would be poor timing.

I took one CO2 hit where I had a pretty strong urge NOT to get off the loop. Is that just caused by not wanting to leave a breathing source? Or is something else going on?

Depth-junkie · 1st November 2007, 21:44

Quote:

I thought that elevated CO2 exposure increased susceptability to an O2 hit? If so, maybe hitting a hot mix would be poor timing.

Exactly, going from a high helium content mix to a lower helium mix whilst also spiking PP02 is not the smartist thinking in the world where CO2 is involved.

You know Co2 being a catalist for O2 susceptability and all that, never mind a bit of IBCD thrown in for good measure.

Mmmmmmm good plan, more interweb gurus for ya

ATB
Gareth

David Pye · 1st November 2007, 22:23

Quote: (Originally Posted by Depth-junkie)

You know Co2 being a catalist for O2 susceptability and all that, never mind a bit of IBCD thrown in for good measure.

Mmmmmmm good plan, more interweb gurus for ya

ATB
Gareth

Seeing as you're mentioning the interweb gurus, could I just ask what actual evidence there is that CO2 is a catalyst for O2 susceptibility? I'm not saying that it isn't, just that I'd like to know what evidence there is to support that.

I can understand IBCD, but the point above seems to be a widely held belief, but I'm not personally aware of the physiological mechanisms that might underly it.

David

Bobnob · 1st November 2007, 22:33

Quote: (Originally Posted by David Pye)

Seeing as you're mentioning the interweb gurus, could I just ask what actual evidence there is that CO2 is a catalyst for O2 susceptibility? I'm not saying that it isn't, just that I'd like to know what evidence there is to support that.

I can understand IBCD, but the point above seems to be a widely held belief, but I'm not personally aware of the physiological mechanisms that might underly it.

David

google m8 ,

Depth-junkie · 1st November 2007, 22:40

Quote: (Originally Posted by Bobnob)

google m8 ,

ATB
Gareth

1st November 2007, 20:25	#11 (permalink)
Simon Mitchell New Member Current Rebreather/s: MK 15.X Other Rebreather/s: Join Date: May 2005 Location: New Zealand Posts: 168	Re: C02 Retention / Decay times Quote: (Originally Posted by womble) The problem is, CO2 has a higher affinity to haemaglobin than O2, so you have to wait for all the CO2 to be flushed out of your system. No, this is not the problem. The problem is that you are hypoventilating in relation to the CO2 you are producing (in retention), or that you are rebreathing CO2 (in scrubber failure). Quote: (Originally Posted by womble) Theoretically this would be better achieved by a higher PPo2, but there is also the increased risk of oxtox if breathing high PPO2 gas with significant CO2 retention . . . So is this an argument for carrying a not-very-hot deep bailout?? Say PPO2 1.5-1.6?? No its not. The last thing you want to do in the middle of a CO2 toxicity event is increase your PO2, even by a little. If anything, there might be an argument for a very light (helium-rich) bailout so that if you do bail in the middle of a CO2 (hit) the work of breathing is as low as you can possibly make it. Regards, Simon M
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1st November 2007, 20:31	#12 (permalink)
Dsix36 Going Down? Current Rebreather/s: Optima Other Rebreather/s: Join Date: Aug 2007 Location: Deerfield Beach, Florida Posts: 976	Re: C02 Retention / Decay times Quote: (Originally Posted by womble) Theoretically this would be better achieved by a higher PPo2, but there is also the increased risk of oxtox if breathing high PPO2 gas with significant CO2 retention . . . So is this an argument for carrying a not-very-hot deep bailout?? Say PPO2 1.5-1.6?? "not-very-hot" What do you consider hot? I was trained to run a PPO2 of 1.2 under most normal circumstances and maybe bump it up for deco. 1.6 is absolute max. __________________ THE MORE THAT I LEARN, THE MORE THAT I STILL NEED TO LEARN!!!!!!
(Online)

1st November 2007, 20:48	#13 (permalink)
womble Custom Title Allowed! Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: UK Posts: 188	Re: C02 Retention / Decay times Quote: (Originally Posted by Simon Mitchell) No, this is not the problem. The problem is that you are hypoventilating in relation to the CO2 you are producing (in retention), or that you are rebreathing CO2 (in scrubber failure). Yes you are hypoventilating, partly due to the psychological stress, but partly due to the higher levels of CO2 in your body. It is after all CO2 levels in the body that stimulates the breathing reflex. So as long as you have higher CO2 levels in your body, you will breathe heavier. No its not. The last thing you want to do in the middle of a CO2 toxicity event is increase your PO2, even by a little. Do you have any evidence to back this up? So say you are diving a setpoint of 1.3, and your deep bailout has a PPO2 of 1.4-1.5 (Which is quite common practice) then what?? If anything, there might be an argument for a very light (helium-rich) bailout so that if you do bail in the middle of a CO2 (hit) the work of breathing is as low as you can possibly make it. Regards, Simon M Quote: (Originally Posted by Dsix36) "not-very-hot" What do you consider hot? I was trained to run a PPO2 of 1.2 under most normal circumstances and maybe bump it up for deco. 1.6 is absolute max. I would consider PPO2 greater than 1.7 hot. remember, I am talking about bailout here, not loop PPO2. __________________ "What could possibly go wrong?? . . "
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1st November 2007, 20:54	#14 (permalink)
Dsix36 Going Down? Current Rebreather/s: Optima Other Rebreather/s: Join Date: Aug 2007 Location: Deerfield Beach, Florida Posts: 976	Re: C02 Retention / Decay times Quote: (Originally Posted by womble) I would consider PPO2 greater than 1.7 hot. remember, I am talking about bailout here, not loop PPO2. Oops, I should read better __________________ THE MORE THAT I LEARN, THE MORE THAT I STILL NEED TO LEARN!!!!!!
(Online)

1st November 2007, 20:57	#15 (permalink)
Mark Chase I go down for ages Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,561	Re: C02 Retention / Decay times Quote: (Originally Posted by womble) I would consider PPO2 greater than 1.7 hot. remember, I am talking about bailout here, not loop PPO2. I generally avoid saying it in public but on an immediate ascent dive I often have a max tolerance on bailout of 2.0bar. On a return to shot is a must or overhead environment i keep it below 1.6. _____ Some interesting stuff there Simon. I have always looked to instantly lower the helium content on bailout to reduce the deco commitment. So as an example, i dive 14/65 but have 18/45 for bailout. Based on what your saying I should perhaps consider upping the helium content to reduce WOB as a priority over the additional deco. ATB Mark __________________ Is it supposed to make that noise ? I took my unit to the dive shop and demanded they bolt on every thing that would fit. Join my elite diving teem and get a Tshirt "Doing It Chasey"Hammerhead Eccr Advanced Diving System
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1st November 2007, 21:02	#16 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 556	Re: C02 Retention / Decay times Quote: (Originally Posted by womble) I would consider PPO2 greater than 1.7 hot. remember, I am talking about bailout here, not loop PPO2. I thought that elevated CO2 exposure increased susceptability to an O2 hit? If so, maybe hitting a hot mix would be poor timing. I took one CO2 hit where I had a pretty strong urge NOT to get off the loop. Is that just caused by not wanting to leave a breathing source? Or is something else going on?
(Offline)

1st November 2007, 21:44	#17 (permalink)
Depth-junkie 10/52 Psycho Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Aug 2005 Location: Wrexham Posts: 291	Re: C02 Retention / Decay times Quote: I thought that elevated CO2 exposure increased susceptability to an O2 hit? If so, maybe hitting a hot mix would be poor timing. Exactly, going from a high helium content mix to a lower helium mix whilst also spiking PP02 is not the smartist thinking in the world where CO2 is involved. You know Co2 being a catalist for O2 susceptability and all that, never mind a bit of IBCD thrown in for good measure. Mmmmmmm good plan, more interweb gurus for ya ATB Gareth __________________ Alpine low rider of the P.D.D.T
(Offline)

1st November 2007, 22:23	#18 (permalink)
David Pye CK 69+Shearwater Pursuit Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: May 2006 Location: Newcastle Upon Tyne Posts: 166	Re: C02 Retention / Decay times Quote: (Originally Posted by Depth-junkie) You know Co2 being a catalist for O2 susceptability and all that, never mind a bit of IBCD thrown in for good measure. Mmmmmmm good plan, more interweb gurus for ya ATB Gareth Seeing as you're mentioning the interweb gurus, could I just ask what actual evidence there is that CO2 is a catalyst for O2 susceptibility? I'm not saying that it isn't, just that I'd like to know what evidence there is to support that. I can understand IBCD, but the point above seems to be a widely held belief, but I'm not personally aware of the physiological mechanisms that might underly it. David
(Online)

1st November 2007, 22:33	#19 (permalink)
Bobnob Sock Puppet banned - gobfish1 back Current Rebreather/s: Inspiration Classic Other Rebreather/s: Inspiration Classic Inspiration Vision Evolution Join Date: Oct 2007 Location: south of north Posts: 32	Re: C02 Retention / Decay times Quote: (Originally Posted by David Pye) Seeing as you're mentioning the interweb gurus, could I just ask what actual evidence there is that CO2 is a catalyst for O2 susceptibility? I'm not saying that it isn't, just that I'd like to know what evidence there is to support that. I can understand IBCD, but the point above seems to be a widely held belief, but I'm not personally aware of the physiological mechanisms that might underly it. David google m8 ,
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1st November 2007, 22:40	#20 (permalink)
Depth-junkie 10/52 Psycho Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Aug 2005 Location: Wrexham Posts: 291	Re: C02 Retention / Decay times Quote: (Originally Posted by Bobnob) google m8 , ATB Gareth __________________ Alpine low rider of the P.D.D.T
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