Binding haemoglobin ?

[daj72]

I need to understand this correctly, perhaps someone can help;

When oxygen is binding to haemoglobin will all 4 haem-groups automatic be occupied ??

I understand that the Partial pressure is important for the saturation, and when one group is getting occupied it makes it easier for the next group to get occupied and so on, but can only 1, 2 or 3 groups be occupied, and if so how will that show on the saturation, if at all ??

 

[MSDeltaFlt]

If you read every single word in the chapter, and even on the articles when you use your Google function, you'll notice the these little words when referring to O2 binding with hemoglobin: can, or up to.

Since CO has a higher affinity for binding than O2, that would also mean some sites would have O2 and others CO even on the same molecule. Which is why we want to use 100% O2 and PEEP/CPAP on CO poisoning.

 

[silver]

I need to understand this correctly, perhaps someone can help;

When oxygen is binding to haemoglobin will all 4 haem-groups automatic be occupied ??

I understand that the Partial pressure is important for the saturation, and when one group is getting occupied it makes it easier for the next group to get occupied and so on, but can only 1, 2 or 3 groups be occupied, and if so how will that show on the saturation, if at all ??

Hemoglobin is one of the best models for understanding proteins and is key for biochemistry (though you can say that biochem is not needed for paramedicine).

This online textbook explains it well: http://www.ncbi.nlm.nih.gov/books/NBK22596/

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[ah2388]

If you read every single word in the chapter, and even on the articles when you use your Google function, you'll notice the these little words when referring to O2 binding with hemoglobin: can, or up to.

Since CO has a higher affinity for binding than O2, that would also mean some sites would have O2 and others CO even on the same molecule. Which is why we want to use 100% O2 and PEEP/CPAP on CO poisoning.

Can you dive into the PEEP/CPAP discussion when related to suspected CO poisoning.

 

[JPINFV]

If you read every single word in the chapter, and even on the articles when you use your Google function, you'll notice the these little words when referring to O2 binding with hemoglobin: can, or up to.

Personally, I'm struggling a bit with the question. Sure, "can" or "up to" is present. Similarly, it makes sense to say, "well, it can bind 0-4 molecules" (kinda of like how a gas tank isn't just full or empty). On the other hand, when one molecule binds, there's a conformational change from a tense state to a relaxed state, which increases the hemoglobin molecule's affinity for oxygen. So it's possible that in the lungs it's an all or nothing, but in the capillaries you can drop some, but not all, of the oxygen.

 

[Handsome Robb]

Can you dive into the PEEP/CPAP discussion when related to suspected CO poisoning.

My understanding is with the CPAP+100% FiO2 you are trying to 'force' the CO off the hemoglobin and replacing it with O2. The CO has a greater affinity but it is still possible to 'force' the CO out and the O2 in. Higher PaO2 = better chance of O2 binding with the hemoglobin rather than CO binding with it. Unlike in cyanide poisoning where medications are required to break down the cyanide in order to disassociate it from the hemoglobin.

 

[JPINFV]

Can you dive into the PEEP/CPAP discussion when related to suspected CO poisoning.

Most likely because more oxygen means it's more likely that oxygen binds instead of CO, thus allowing CO to GTFO. A mental issue I see with people understanding chemistry (including biochemistry) is that chemistry is essentially random. It's possible to take a breath of air and have absolutely no oxygen bind to hemoglobin. It's also extremely unlikely to the point of being laughable simply given the shear number of oxygen molecules that more than a handful are going to find they're way through the alveolar membrane (remember, not all oxygen molecules diffuse across) and find their way to an empty hemoglobin molecule with enough energy (not enough energy, then no reaction) and in the right orientation (These are three dimensional objects after all, and if it's not positioned in the right manner, then it won't attach) to attach to a hemoglobin molecule. The properties (charge, shape, etc) of the hemoglobin makes it more likely that those conditions are going to be met.

 

[MSDeltaFlt]

Can you dive into the PEEP/CPAP discussion when related to suspected CO poisoning.

Sure. Pts with CO poisoning will need 100% FiO2 with PEEP/CPAP of 5cmH2O or more to literally shove the CO off the hemoglobin.

 

[MSDeltaFlt]

Personally, I'm struggling a bit with the question. Sure, "can" or "up to" is present. Similarly, it makes sense to say, "well, it can bind 0-4 molecules" (kinda of like how a gas tank isn't just full or empty). On the other hand, when one molecule binds, there's a conformational change from a tense state to a relaxed state, which increases the hemoglobin molecule's affinity for oxygen. So it's possible that in the lungs it's an all or nothing, but in the capillaries you can drop some, but not all, of the oxygen.

Nothing in life is ever linear. Very few things are either or. The hemoglobin can and do have "up to" 4 molecules of O2. Some have one, some two or three, and even four. But that's not an absolute. One of the reasons, besides the fact that hemoglobin are born in marrow and also die, that you will never have a SaO2 of 100%.

 

[JPINFV]

I'm not arguing that hemoglobin won't have up to 4. In fact, given the dynamics above, in the lungs it's probably more likely to have 4 than have an intermediate level.

 

[Handsome Robb]

I'm still waiting for someone smarter than me to either tell me I'm an idiot or that I have the basic idea of it

From reading what Delta said I think I'm on the right path but I'm wondering if there's more too it or if it's one of those things I should just leave alone and accept it...

 

[daj72]

Hi guys,

Thank you for all the reply´s so far, and JPINFV is saying what I'm thinking also;

Personally, I'm struggling a bit with the question. Sure, "can" or "up to" is present. Similarly, it makes sense to say, "well, it can bind 0-4 molecules" (kinda of like how a gas tank isn't just full or empty).

But MSDeltaFlt gives a fine answer to that. although undocumented But silver gives a good link.

Yesterday a talked to a anesthesiologist, and even he couldnt definitely explain if a hemo group was binding 1, 2, 3 or 4 !
He´s conclusion was that the sat.% O2 was a "average" of the total
oxyhemoglobin, whether it is binding 1,2, 3 or 4.

 

[MSDeltaFlt]

Hi guys,

Thank you for all the reply´s so far, and JPINFV is saying what I'm thinking also;



But MSDeltaFlt gives a fine answer to that. although undocumented But silver gives a good link.

Yesterday a talked to a anesthesiologist, and even he couldnt definitely explain if a hemo group was binding 1, 2, 3 or 4 !
He´s conclusion was that the sat.% O2 was a "average" of the total
oxyhemoglobin, whether it is binding 1,2, 3 or 4.

And here's my stance on the subject. Until the data changes the words "can" and "up to" to either "always" or "never", I'm going to believe that hemoglobin "can" bind "up to" 4 O2 molecules.

 

[silver]

And here's my stance on the subject. Until the data changes the words "can" and "up to" to either "always" or "never", I'm going to believe that hemoglobin "can" bind "up to" 4 O2 molecules.

With the data we can certainly say that the cooperativity has an affect on the overall saturation though.

Its the mystery of molecules, atoms, and subatomic particles. We know somewhat where they should be most of the time and what they are doing most of the time, and as a result make general rules/laws (for example electron shells) and/or statements with conditions like "can bind up to."

 

[systemet]

* My understanding is that the pulse oximeter detects the taut / tense deoxyhemoglobin with one wavelength of light, and the relaxed oxyhemoglobin with another. I don't think it's able to distinguish between 1-, 2-, 3- and 4- bound oxygen atoms.

* This is a stochastic process. Oxygen is continually binding and unbinding from the hemoglobin. But at a given moment, a certain percentage of sites as likely to be occupied. As the pO2 increases, the likelihood that any one site is occupied at a given point in time also increases, and the greater the likelihood that any individual molecule will be 3- or 4- oxygenated.

* Remember SpO2 (pulse oximetry) is an estimate of arterial oxygen saturation percentage (SaO2). It's an indirect measurement, and while it's fairly accurate, most device become less reliable as they start reporting SpO2 readings of < 85%.

 

[JPINFV]

It's an indirect measurement, and while it's fairly accurate, most device become less reliable as they start reporting SpO2 readings of < 85%.

Of course once you get that low accuracy isn't as important. Profound hypoxia is more important than knowing just how profound it is.