amitjosh
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Why does CO poisoning shift O2 dissociation curve to the left?
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| MLF
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CO has 200x more affinity for Hb then oxygen, meaning when its occupying the four groups on Hb, it doesn't let Oxygen get on, and the curve is shifted to the LEFT where no oxygen can be given to tissues resulting in hypoxia and tissue death. Remember, if curve shifts to the LEFT, you are unloading oxygen and thats good, so you can provide your tissues with oxygen, but anytime to the right, you can't provide oxygen to tissues. In fetal hb, the curve is to the left, because you want oxygen hooked on tightly to fetal hb so it can travel from mom to fetus instead of unloading to tissues, so in that case, its a good thing. Hope I didn't confuse you further!!!
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| santaclara
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well i agree with MLF.
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| amitjosh
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Hi, Thanks for the reply but I could not get your point.
Let me briefly give my point of view -
Since there is tissue hypoxia in CO poisoning, we want more O2 to be delivered to the tissues and so the curve should infact shift to the right.
But in nature, the curve shifts to the left so though the capacity to load O2 near the alveoli increases but unloading of O2 in the tissues (which according to me is very important in hypoxia) decreases. So, would it not have been better if the curve shifted to the right?
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| MLF
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Yes it would be, i was just giving you examples of when its good for the curve to shift to the right and left. But you are absolutely correct as well.
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| mani
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i disagree MLF. in CO poisoning the curve is actually shifted to the left where it is difficult to unload the O2 but easier to load it. this shift may be due to chemical nature of CO
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| santaclara
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i m sorry.i just forgot it
IN CO the O2-Hb dissociation curve is shift to the left and carrying capacity is reduced.
in CO poisoning the arterial PO2is normal but oxygen saturation of hemoglobin is depressed.
and also one more thing to detrmine acute CO poisoning is depression of oxygen saturation of Hb.it is useless to get a gas sample b/c po2 is normal b/c pt which come in emergency is breathing room air.
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| MLF
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I am sorry guys, thats suppose to be a typo, now i know what amitjosh was confused about, i'll fix that, i meant CO shifts curve to Left, due to exactly what mani and santaclara said.
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| mani
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no problem MLF, its better to make a mistake now than in the exam. good luck to u
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