urge to breathe and co2 scrubber

Mark Wan · 20th February 2006, 23:00

Discussing rebreathers today with a non-rebreather diver, who's also a physicist. He asked if the scrubber removes all the CO2, will a Rebreather diver have a reduced "urge to breathe"?

Or is it a fact of life that all CO2 scrubbers (even fresh fills at shallow depths in warm water) cannot remove all the co2 from the breathing loop?

Sorry if this question has been asked before, but I couldn't find anything similar when I did a search.

rgds
mark

pchanning · 20th February 2006, 23:04

Great question - no idea, but I would be very interested to know.

There are some medical par excellence types on here who should be able to advise.

dteubner · 20th February 2006, 23:05

Quote: (Originally Posted by Mark Wan)

Discussing rebreathers today with a non-rebreather diver, who's also a physicist. He asked if the scrubber removes all the CO2, will a Rebreather diver have a reduced "urge to breathe"?

rgds
mark

A scrubber should remove all of the CO2 from the inspired gas. (In fact some of the time they probably don't but that's another story).

"The urge to breathe" comes form the CO2 disolved in the blood, not the inspired CO2. There is essentially no CO2 in ordinary room air and you certainly don't need inspired CO2 to breathe.

Dave T

Nick uk. · 20th February 2006, 23:26

Yeh, our bodies create the Co2 as a by-product when burning the O2, and thus giving us the urge to breathe, but i've been doing it for so many years now, i don't wait for the urge, i just do it!!

E-man · 20th February 2006, 23:51

If the scrubbers working properly all the co2 will be scrubbed so you'll have 0.04% (depending on where you live) less co2 in your system per inhale/exhale cycle.

***ScubaDadMiami*** · 21st February 2006, 03:33

I thought that the strongest CO2 receptors that trigger the urge to breathe were in the lungs. So, isn't it the retained CO2 in the lungs that primarily triggers the urge?

Rob Johnson · 21st February 2006, 04:26

Quote: (Originally Posted by ScubaDadMiami)

I thought that the strongest CO2 receptors that trigger the urge to breathe were in the lungs. So, isn't it the retained CO2 in the lungs that primarily triggers the urge?

I could easily be wrong but I was under the impression that the CO2 receptors were actually in the brain.

**nigelh** · 21st February 2006, 07:50

Quote: (Originally Posted by Mark Wan)

Discussing rebreathers today with a non-rebreather diver, who's also a physicist. He asked if the scrubber removes all the CO2, will a Rebreather diver have a reduced "urge to breathe"?

Marginally.
It doesn't matter though. Your breathing drive is based on blood CO2 and running 1.3 or similar bar of O2 through your lungs you are way over-provided for on the O2 side.

Mark Wan · 21st February 2006, 09:57

Quote: (Originally Posted by ScubaDadMiami)

I thought that the strongest CO2 receptors that trigger the urge to breathe were in the lungs. So, isn't it the retained CO2 in the lungs that primarily triggers the urge?

Actually now that people have mentioned it, I remember how it's supposed to work now. Elevated levels of CO2 increase the blood acid level, and the receptors in the brain notice the ph change and this provides the impetus to breathe. So even if the scrubber removes all exhaled CO2, the fact that it was exhaled means that the CO2 has already prompted the brain to breathe.

I guess I should have known the answer before I posted the question

thanks for all the responses.

DonalWalsh · 21st February 2006, 10:45

CO2 and Hydrogen ion dissolved in the blood (as opposed to the partial pressure of the gas in the lungs) are important chemical regulators of respiration. CO2 has the ability to traverse the blood brain barrier and directly stimulate the ventilatory drive centre of the Medulla Oblongata. There are peripheral chemoreceptors in the lung the respond to changes in PaO2 and PaCO2 as well but its the central stimulation that's at the heart of respiratory control

CO2 is also the most important chemical regulator of blood flow to the brain - put simply if PaCO2 is brought too low you'll lose conciousness (try hyperventilating!)

20th February 2006, 23:00	#1 (permalink)
Mark Wan New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Nov 2005 Location: Hammersmith, London Posts: 59	urge to breathe and co2 scrubber Discussing rebreathers today with a non-rebreather diver, who's also a physicist. He asked if the scrubber removes all the CO2, will a Rebreather diver have a reduced "urge to breathe"? Or is it a fact of life that all CO2 scrubbers (even fresh fills at shallow depths in warm water) cannot remove all the co2 from the breathing loop? Sorry if this question has been asked before, but I couldn't find anything similar when I did a search. rgds mark __________________ newbie inspo vision diver
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20th February 2006, 23:04	#2 (permalink)
pchanning PFO free :) Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: fixed! Posts: 454	Re: urge to breathe and co2 scrubber Great question - no idea, but I would be very interested to know. There are some medical par excellence types on here who should be able to advise. __________________ Cheers Paul The key to enlightenment... is survival.
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20th February 2006, 23:05	#3 (permalink)
dteubner Pedant Current Rebreather/s: Sport Kiss Classic Kiss Other Rebreather/s: Join Date: Mar 2005 Location: Adelaide, Australia Posts: 216	Re: urge to breathe and co2 scrubber Quote: (Originally Posted by Mark Wan) Discussing rebreathers today with a non-rebreather diver, who's also a physicist. He asked if the scrubber removes all the CO2, will a Rebreather diver have a reduced "urge to breathe"? rgds mark A scrubber should remove all of the CO2 from the inspired gas. (In fact some of the time they probably don't but that's another story). "The urge to breathe" comes form the CO2 disolved in the blood, not the inspired CO2. There is essentially no CO2 in ordinary room air and you certainly don't need inspired CO2 to breathe. Dave T
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20th February 2006, 23:26	#4 (permalink)
Nick uk. Made in England. Current Rebreather/s: Inspiration Classic Azimuth Other Rebreather/s: Azimuth Join Date: Nov 2005 Location: Viale C.Colombo 75 Marina di Carrara. MS 54036 Italy Posts: 579	Re: urge to breathe and co2 scrubber Yeh, our bodies create the Co2 as a by-product when burning the O2, and thus giving us the urge to breathe, but i've been doing it for so many years now, i don't wait for the urge, i just do it!! __________________ If it aint broke....don't fix it, and if it is.............well......get another one! divechief2000@hotmail.com
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20th February 2006, 23:51	#5 (permalink)
E-man On the loop! Current Rebreather/s: Inspiration Classic Optima Other Rebreather/s: Titan Join Date: Sep 2005 Location: Eastern Coast ;) Posts: 212	Re: urge to breathe and co2 scrubber If the scrubbers working properly all the co2 will be scrubbed so you'll have 0.04% (depending on where you live) less co2 in your system per inhale/exhale cycle.
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21st February 2006, 03:33	#6 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 1,890	Re: urge to breathe and co2 scrubber I thought that the strongest CO2 receptors that trigger the urge to breathe were in the lungs. So, isn't it the retained CO2 in the lungs that primarily triggers the urge? __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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21st February 2006, 04:26	#7 (permalink)
Rob Johnson New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Mar 2005 Location: Oregon Posts: 7	Re: urge to breathe and co2 scrubber Quote: (Originally Posted by ScubaDadMiami) I thought that the strongest CO2 receptors that trigger the urge to breathe were in the lungs. So, isn't it the retained CO2 in the lungs that primarily triggers the urge? I could easily be wrong but I was under the impression that the CO2 receptors were actually in the brain.
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21st February 2006, 07:50	#8 (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: 784	Re: urge to breathe and co2 scrubber Quote: (Originally Posted by Mark Wan) Discussing rebreathers today with a non-rebreather diver, who's also a physicist. He asked if the scrubber removes all the CO2, will a Rebreather diver have a reduced "urge to breathe"? Marginally. It doesn't matter though. Your breathing drive is based on blood CO2 and running 1.3 or similar bar of O2 through your lungs you are way over-provided for on the O2 side. __________________ nigelh
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21st February 2006, 09:57	#9 (permalink)
Mark Wan New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Nov 2005 Location: Hammersmith, London Posts: 59	Re: urge to breathe and co2 scrubber Quote: (Originally Posted by ScubaDadMiami) I thought that the strongest CO2 receptors that trigger the urge to breathe were in the lungs. So, isn't it the retained CO2 in the lungs that primarily triggers the urge? Actually now that people have mentioned it, I remember how it's supposed to work now. Elevated levels of CO2 increase the blood acid level, and the receptors in the brain notice the ph change and this provides the impetus to breathe. So even if the scrubber removes all exhaled CO2, the fact that it was exhaled means that the CO2 has already prompted the brain to breathe. I guess I should have known the answer before I posted the question thanks for all the responses. __________________ newbie inspo vision diver
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21st February 2006, 10:45	#10 (permalink)
DonalWalsh Third Class Snorkeller Current Rebreather/s: Megalodon Other Rebreather/s: Evolution Join Date: Nov 2005 Location: Moving to London in Sept.....which way to the South Coast?? Posts: 136	Re: urge to breathe and co2 scrubber CO2 and Hydrogen ion dissolved in the blood (as opposed to the partial pressure of the gas in the lungs) are important chemical regulators of respiration. CO2 has the ability to traverse the blood brain barrier and directly stimulate the ventilatory drive centre of the Medulla Oblongata. There are peripheral chemoreceptors in the lung the respond to changes in PaO2 and PaCO2 as well but its the central stimulation that's at the heart of respiratory control CO2 is also the most important chemical regulator of blood flow to the brain - put simply if PaCO2 is brought too low you'll lose conciousness (try hyperventilating!)
(Offline)

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