CO Poisoning Question

[Akimbo]

I have found the almost unimaginably small scale is a barrier to most people relating to these concepts. I made these images to scale to help visualize them. We can all relate to the thickness of copier paper but very few can think in terms of microns.

Cells relative to gas molecules is even harder:

Of course human cells aren't as consistent in size or geometry as ball bearings but the averages are close enough for this discussion.

 

[Duke Dive Medicine]

@Duke Dive Medicine I find it interesting that CO supposedly has 210 times the affinity to bond with heme than O2 (it would be interesting to understand how that figure is derived) yet it will give up the covalent bond based on the diffusion gradient caused by high concentration of O2....it still has me wondering if there is something else going on that causes the CO to more freely disassociate from the heme such as increased alkalinity of the blood due to the greater amount and higher PPO2 during treatment. It is difficult for me to accept that it is simply due to the gradient between the two. This just tells me I need to do more reading/research.

-Z[/QUOTE]

Hi @Zef and all,

This exchange piqued my curiosity enough that I reached out to Dr. Barry Allen, one of the PhD researchers at the Duke Center for Hyperbaric Medicine and Environmental Physiology. Here was his answer via email:

EH/DDM:
In a hyperoxic environment (either normobaric or hyperbaric), is there anything besides the diffusion gradient across the hemoglobin/alveolar continuum that causes CO to detach from hemoglobin? Is there any biochemistry involved that hyperbaric oxygenation would accelerate, or is it simply the diffusion gradient?

BA, PhD:
"Here’s my 5-dollar answer to your 50-dollar question.

As you know, CO acts as a poison by displacing oxygen from hemoglobin. But it also increases the affinity of hemoglobin for the decreased amount oxygen that is still bound to hemoglobin, slowing its release to tissues—a “double whammy”.

Here’s the reaction of CO with hemoglobin (Hb):

CO + 02Hb [double arrows] 02 + COHb

The double arrows mean that the reaction can go either way, but CO has an affinity for Hb that is 200 times that for 02 , so the reaction preferentially goes to the right. I say “preferentially” because the “back-reaction” (COHb [single arrow] 02Hb) is also happening, but at a much, much slower rate.

Now, add many more oxygen molecules (i.e. hyperbaric oxygenation), and the rate of the back-reaction increases. This chemical effect is described by the Law of Mass Action, “the principle that the rate of a chemical reaction is proportional to the masses of the reacting substances.” This results in “competitive displacement”.

During the administration of hyperbaric oxygenation, there is a large increase in the amount of oxygen that is dissolved in the plasma, and this can keep tissues alive while CO is being displaced from hemoglobin and ultimately exhaled. J.S. Haldane discovered this effect in the late 19th Century and published his findings in 1895: “To account for this relation between oxygen tension and the effect of carbonic oxide [i.e. CO] the hypothesis suggested itself that the higher the oxygen tension the less dependent an animal is on its red corpuscles as oxygen carriers, since the oxygen simply dissolved in the blood becomes considerable when the oxygen tension is high.”

So, the answer to your question is “competitive displacement” (also called “competitive inhibition”). Diffusion can only happen after the displacement occurs."

Best regards,
DDM

 

[Storker]

a covalent bond is weaker than an ionic bond

Cite, please? A decent chemistry textbook is good enough for me.

 

[Zef]

Cite, please? A decent chemistry textbook is good enough for me.

I am not a chemist. I am just recalling info, perhaps erroneously, from my long ago days as a student. I have always had the impression that ionic bonds were stronger than covalent bonds due to the exchange of electrons in ionic bonds and the lattice effect vs the sharing of electrons in covalent bonds. I know that my statement was a broad generalization and in actuality the bond strength is entirely dependent on which specific atoms are bonding together.

Covalent Bonds vs Ionic Bonds - Difference and Comparison | Diffen0
Chemical Bonds

-Z

 

[Storker]

I am not a chemist. I am just recalling info, perhaps erroneously, from my long ago days as a student.

May I then respectfully suggest that you don't make definitive statements about things you are recalling, perhaps erroneously, from long ago? At least put in a disclaimer or two? Because some of the things you have said in this thread have been plain wrong.

Covalent bond strength isn't comparable to ionic lattice energy (cite). The average bond enthalpy of of the C-H bond in methane is 415 kJ/mol, and the bond enthalpy of the H-H bond in H2 is 436 kJ/mol (ibid.) The lattice enthalpy of NaCl is 787 kJ/mol (cite). So why does NaCl dissolve in water as free, dissociated ions? Because the lattice enthalpy is the enthalpy change when going from solid salt to gaseous ions, and that's not what happens here. You have to consider the end state, which is sodium and chloride ions in water. So the net enthalpy change is only 3.9 kJ/mol. Which still is unfavorable, but we're just comparing enthalpies here. The other important driver in chemical reactions is entropy. Look at a standard ice pack. The dissolution of urea or ammonium nitrate in water is highly endothermic, IOW if we just looked at the enthalpy change, it would never happen. But here comes entropy and drives the dissolution anyway, and the enthalpy change is provided by the cooling of the solution.

Tl,dr: you can't just compare "bond strength" of covalent bonds and ionic bonds to say which is the "strongest". You have to consider the whole system, both starting point and end state.

And yes, I have a chemistry degree. In case someone was still wondering about that. And thermodynamics is actually quite interesting, because that's what makes everything work. Literally everything.

 

[Zef]

May I then respectfully suggest that you don't make definitive statements about things you are recalling, perhaps erroneously, from long ago? At least put in a disclaimer or two? Because some of the things you have said in this thread have been plain wrong.

Covalent bond strength isn't comparable to ionic lattice energy (cite). The average bond enthalpy of of the C-H bond in methane is 415 kJ/mol, and the bond enthalpy of the H-H bond in H2 is 436 kJ/mol (ibid.) The lattice enthalpy of NaCl is 787 kJ/mol (cite). So why does NaCl dissolve in water as free, dissociated ions? Because the lattice enthalpy is the enthalpy change when going from solid salt to gaseous ions, and that's not what happens here. You have to consider the end state, which is sodium and chloride ions in water. So the net enthalpy change is only 3.9 kJ/mol. Which still is unfavorable, but we're just comparing enthalpies here. The other important driver in chemical reactions is entropy. Look at a standard ice pack. The dissolution of urea or ammonium nitrate in water is highly endothermic, IOW if we just looked at the enthalpy change, it would never happen. But here comes entropy and drives the dissolution anyway, and the enthalpy change is provided by the cooling of the solution.

Tl,dr: you can't just compare "bond strength" of covalent bonds and ionic bonds to say which is the "strongest". You have to consider the whole system, both starting point and end state.

And yes, I have a chemistry degree. In case someone was still wondering about that. And thermodynamics is actually quite interesting, because that's what makes everything work. Literally everything.

Thanks.

-Z

 

[chillyinCanada]

CA, for one, requires CO detectors in new construction, at time of sale, and in rentals.



I had an extra so I put it near the floor in the garage. The gas hot water heater is there and it doubles as my shop. Also the dogs have a door to the outside, and I figure they would rather go out in the heat rather than listen to it.

When I got my first CO monitor, I put it low in the lower level of the house, not too far from the furnace.

When the furnace was replaced 4 years ago, the techs came up and replaced the thermostat and installed a new CO monitor. The tech put it up on the wall at the same level as the thermostat. I questioned the placement and he informed me that I was wrong. Please advise me.

 

[chillyinCanada]

I'm sure the analogy evolved from years of trying to explain complex microbiology to diver-sailors with widely varied backgrounds. Same with "biologically inert". Finding common ground between young seaman that may have dropped out of school to officers with PhDs in physiology is almost as hard as finding common ground on the Internet.

Seriously, this kind of discussion is valuable. US Navy diving schools rarely had to communicate with different nationalities, vastly different cultures, and non-native english speakers like ScubaBoard. Discovering phrases that are understandable and technically correct can benefit everyone.

I'd been trying to figure out what hemoglobin was so of course googled. Hmm, says I, "then what is hemoglobolin?" To Google, I returned. Aha, English vs American
And then there's haemoglobin and haemoglobolin.

 

[DandyDon]

When I got my first CO monitor, I put it low in the lower level of the house, not too far from the furnace.

Yeah, that was wrong. Opinions actually vary if you ask the question on google, some say knee high, some say five feet from floor, some say ceiling mount is ok while others disagree, but they seem to agree to avoid heating sources and humid areas as those can give false alarms. Your heater may well give a small amount of CO on start up but not enough to matter for the room.

One for each bedroom is best so you'll hear it even if asleep as well at least one for each floor.

The tech put it up on the wall at the same level as the thermostat. I questioned the placement and he informed me that I was wrong. Please advise me.

CO is only slightly lighter than air so while it will tend to rise, even the gentlest air currents will spread it out through the room. Two of mine are plug-ins with battery backup so one is knee high in a plug and the other is five feet high.

I think this one by a fire department is better at explaining: https://www.merrimacknh.gov/sites/m.../file/proper_placement_of_carbon_monoxide.pdf

 

[chillyinCanada]

Yeah, that was wrong. Opinions actually vary if you ask the question on google, some say knee high, some say five feet from floor, some say ceiling mount is ok while others disagree, but they seem to agree to avoid heating sources and humid areas as those can give false alarms. Your heater may well give a small amount of CO on start up but no enough to matter for the room.

One for each bedroom is best so you'll hear it even if asleep as well at least one for each floor.


CO is only slightly lighter than air so while it will tend to rise, even the gentlest air currents will spread it out through the room. Two of mine are plug-ins with battery backup so one is knee high in a plug and the other is five feet high.

I think this one by a fire department is better at explaining: https://www.merrimacknh.gov/sites/m.../file/proper_placement_of_carbon_monoxide.pdf

Thanks for this.

The one on the lowest floor near the furnace, is actually in another room, just slightly around the corner. So, I'm good though a few monitors short, apparently.