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#1
09-30-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,186 Threads: 119 Thanked 815 Times in 434 Posts Reputation: 825

friends..,

can anyone explain me the difference between oxygen binding capacity and oxygen saturation(i know it's proportion but).......???
everytime i study it again and again i'm getting confused...(also confused with goljan and kudrath explanation)......
amount of oxygen bound to hemoglobin----is oxy.saturation or oxy.binding capacity..???

and do tell me the changes of both of them in CO :sorryoisoning,methemoglobinemia,anemia,CN poisoning

thank you
 The above post was thanked by: Nijhum (10-03-2012)

#2
10-01-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 763 Threads: 77 Thanked 1,338 Times in 347 Posts Reputation: 1348

Blood O2 content = O2 binding capacity * SaO2 + PO2

O2 binding capacity is determined by hemoglobin concentration i.e. 1 gram of hb binds 1.34 ml O2. So if we assume that normal Hb is around 15 g/dl then O2binding capacity is 1.34 * 15 = 20.1 ml/dl.
Sao2 is % Hb bound to 02.

* Methemoglobin absorbs light at wavelengths that also absorb deoxyhemoglobin and oxyhemoglobin. Thus, methemoglobin interferes with the colorimetric testing that is used to obtain the percentage of oxyhemoglobin to deoxyhemoglobin

oxygen binding capacity has to go down,cause met-Hb and CO-Hb can't bind 02. So available Hb for 02 is deacreased, thus Hb concetration may be normal, but functional amount will be less, which will decrease O2BC.

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 The above post was thanked by: Lara (10-01-2012), MANIAKOS (10-01-2012), venky2600 (10-01-2012)
#3
10-01-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,186 Threads: 119 Thanked 815 Times in 434 Posts Reputation: 825

thanks alot

can you also tell me the chnges in CN poisoning too...??

so in anemia Pao2 and Sao2 are normal and decreased O2 binding capactity(so decreased total O2 content)....is that right..??

can you also give other examples....? like hypoventilation,embolism changes

and also" oxygen binding capacity has to go down,cause met-Hb and CO-Hb can't bind 02".....why o2 binding capacity decreases...i mean it depends on hb concentration right?....i'm confused here...

thanks

#4
10-01-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 763 Threads: 77 Thanked 1,338 Times in 347 Posts Reputation: 1348

Quote:
 Originally Posted by venky2600 thanks alot can you also tell me the chnges in CN poisoning too...?? so in anemia Pao2 and Sao2 are normal and decreased O2 binding capactity(so decreased total O2 content)....is that right..?? can you also give other examples....? like hypoventilation,embolism changes thanks
Well i assume that CN will act differently than met-hb and Co-hb.
Sa02 will be higher than in these cases. Cause it inhibits peripheral o2 consumption by decreasing oxydative phosphorilation( inhibits Cytochrome oxidase aka Complex IV a/a3).

Hypoventilation will decrease Po2 in blood and Sa02. O2 binding capacity will remain unchanged.if prolonged EPO will increase HB and Binding cap will increase too.

PE - since lung is ventilated but not perfused it will have similar effect like hypoventilation. it depends what proportion of lung is affected. it can adapt with hypoxic vasocontiction and keep blood 02 in normal range.

again if i wrote smth wrong correct.
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Step 1 - 244 [✔] Step 2 CK - 246 [✔] Step 2 CS [✔] Step 3 - 228 [✔] Match [EMORY SOM] YOG: 2013, 4 Months of USCE University Hospital
 The above post was thanked by: venky2600 (10-01-2012)
#5
10-01-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,186 Threads: 119 Thanked 815 Times in 434 Posts Reputation: 825

oxygen binding capacity has to go down,cause met-Hb and CO-Hb can't bind 02".....
why o2 binding capacity decreases...i mean it depends on hb concentration right?(hb binding sites are occupied by CO,,,so it decreases hb concentration???)....i'm confused here,so i started this topic...
thanks..
#6
10-01-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 763 Threads: 77 Thanked 1,338 Times in 347 Posts Reputation: 1348

Quote:
 Originally Posted by venky2600 from your statement oxygen binding capacity has to go down,cause met-Hb and CO-Hb can't bind 02"..... why o2 binding capacity decreases...i mean it depends on hb concentration right?(hb binding sites are occupied by CO,,,so it decreases hb concentration???)....i'm confused here,so i started this topic... thanks..
Well. it depends on 2 things i assume.
I. amount of Hb is present
II.is it functional? can it bind oxygen? since met-hb and CO-hb are no more able to bind 02,hence oxygen binding capacity will decrease.

these stuff is always associated with confusion. i'm not sure too.
__________________
Step 1 - 244 [✔] Step 2 CK - 246 [✔] Step 2 CS [✔] Step 3 - 228 [✔] Match [EMORY SOM] YOG: 2013, 4 Months of USCE University Hospital
#7
10-01-2012
 USMLE Forums Scout Steps History: --- Posts: 46 Threads: 1 Thanked 27 Times in 18 Posts Reputation: 37

why o2 binding capacity decreases...i mean it depends on hb concentration right?(hb binding sites are occupied by CO,,,so it decreases hb concentration???)....i'm confused here,so i started this topic...
thanks..[/QUOTE]

--The oxygen binding capacity decreases when their is either loss or dysfunction of hemoglobin. So yes it does depend on Hb conc.
So in relation to loss which is seen in anemia, the SaO2 would be normal because their is nothing wrong with the oxygen saturation, but the RBC mass decreases so the amount of Hb present for oxygen binding capacity decreases.
Whereas, during dysfunction seen in CO and methemoglobinemia, both SaO2 and oxygen binding capacity decrease. In CO, the CO2 is bound to oxygen very tightly, it decreases the amount of Hb for oxygen to bind , so your right the O2 binding sites on Hb decrease.
In methemoglobinemia Iron in heme oxidized to Fe3+ which cannot bind to oxygen, again the oxygen binding capacity decreases and so does the oxygen saturation of blood.
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 The above post was thanked by: neelima208 (10-04-2012), venky2600 (10-01-2012)
#8
10-02-2012
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 331 Threads: 39 Thanked 308 Times in 117 Posts Reputation: 318

Quote:
 Originally Posted by venky2600 thanks alot can you also tell me the chnges in CN poisoning too...?? so in anemia Pao2 and Sao2 are normal and decreased O2 binding capactity(so decreased total O2 content)....is that right..?? can you also give other examples....? like hypoventilation,embolism changes and also" oxygen binding capacity has to go down,cause met-Hb and CO-Hb can't bind 02".....why o2 binding capacity decreases...i mean it depends on hb concentration right?....i'm confused here... thanks

In methemoblobinemia and CO poisoning only Oxygen saturation goes down, which decreases the total oxygen content of blood.

The oxygen binding capacity (which is related to HB amount) is normal and so is PaO2, because you have the same amount of HB, but the HB can not bind the normal amount of O2 to give a saturation of 94-96%. Instead Hb can bind only 2 oxygen molecules (instead of 4) which will give a saturation of 50%.
 The above post was thanked by: drZoe (10-02-2012)
#9
10-02-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,186 Threads: 119 Thanked 815 Times in 434 Posts Reputation: 825

Quote:
 Originally Posted by Teona In methemoblobinemia and CO poisoning only Oxygen saturation goes down, which decreases the total oxygen content of blood. The oxygen binding capacity (which is related to HB amount) is normal and so is PaO2, because you have the same amount of HB, but the HB can not bind the normal amount of O2 to give a saturation of 94-96%. Instead Hb can bind only 2 oxygen molecules (instead of 4) which will give a saturation of 50%.
hey.....in both CO poisoning and methemoglobinemia oxygen binding capacity also decreases along with saturation %......

what @mizzy said is true.....i saw the physio resp. video again....(he also said the same thing...and also given in pathoma as"Decreased O,-carrying capacity arises with hemoglobin (Hb) loss or dysfunction.")
ya it's little confusion..but be conclude from that as oxygen binding capacity implies not only on Hb concentration/amount but also dysfunction of Hb(CO and methemoglobinemia).....O2 binding sites are occupied right...?
it cleared for me finally yesterday...
#10
10-02-2012
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 331 Threads: 39 Thanked 308 Times in 117 Posts Reputation: 318

Quote:
 Originally Posted by venky2600 hey.....in both CO poisoning and methemoglobinemia oxygen binding capacity also decreases along with saturation %...... what @mizzy said is true.....i saw the physio resp. video again....(he also said the same thing...and also given in pathoma as"Decreased O,-carrying capacity arises with hemoglobin (Hb) loss or dysfunction.") ya it's little confusion..but be conclude from that as oxygen binding capacity implies not only on Hb concentration/amount but also dysfunction of Hb(CO and methemoglobinemia).....O2 binding sites are occupied right...? it cleared for me finally yesterday...
Thank you for the explanation. You are right. I misunderstood some things from Goljan. I guess it was kind of confusing.

 Tags Physiology-, Respiratory-

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