When p50 is decreased, there's an increase affinity to Oxygen so it results in hypoxia and has a reflective polycythemia. What if the question stem says P50 is increased, what would the pt most likely to develop? Can you explain please? Thanks.
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Step I P50 Question
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Are you talking about left shift and right shift of the hemoglobin oxygen dissociation curve?
Think of left shift and right shift as reaction of Hgb to an altered metabolic state that then has consequence on oxygen loading and unloading, which are usually adaptive but not always so.
For example, if there is tissue ischemia creating a lactic acid build up, that lowers the pH (increased [H+]) and causes a right shift, meaning more O2 will be unloaded at those tissues by the blood that reaches it, which is probably a good thing.
However, one of the reasons that alkalosis is a really bad thing is that it does the opposite and Hgb holds on tighter to O2 and unloads less at target tissues.
IMO questions tend to give you the metabolic scenario (metabolic acidosis vs respiratory alkalosis vs CO poisoning) and expect you to know the shift and the consequence of that shift. A question that just says "theres a right shift, what happens" doesn't really make much sense unless the answer is "decrease affinity of Hgb for O2"
For example, if there is tissue ischemia creating a lactic acid build up, that lowers the pH (increased [H+]) and causes a right shift, meaning more O2 will be unloaded at those tissues by the blood that reaches it, which is probably a good thing.
However, one of the reasons that alkalosis is a really bad thing is that it does the opposite and Hgb holds on tighter to O2 and unloads less at target tissues.
IMO questions tend to give you the metabolic scenario (metabolic acidosis vs respiratory alkalosis vs CO poisoning) and expect you to know the shift and the consequence of that shift. A question that just says "theres a right shift, what happens" doesn't really make much sense unless the answer is "decrease affinity of Hgb for O2"
Think of left shift and right shift as reaction of Hgb to an altered metabolic state that then has consequence on oxygen loading and unloading, which are usually adaptive but not always so.
For example, if there is tissue ischemia creating a lactic acid build up, that lowers the pH (increased [H+]) and causes a right shift, meaning more O2 will be unloaded at those tissues by the blood that reaches it, which is probably a good thing.
However, one of the reasons that alkalosis is a really bad thing is that it does the opposite and Hgb holds on tighter to O2 and unloads less at target tissues.
IMO questions tend to give you the metabolic scenario (metabolic acidosis vs respiratory alkalosis vs CO poisoning) and expect you to know the shift and the consequence of that shift. A question that just says "theres a right shift, what happens" doesn't really make much sense unless the answer is "decrease affinity of Hgb for O2"
Thanks - I understand left and right shift and I also like to think of Right shift as you are doing exercise (increase H, increase Temp, increase CO2, increased 2,3 DPG)...
The Q asks that there's a rare Hb abnormality that results in P50 from being 26mmHg to 20mmHg (so it's a left shift) - and asks what will develop in the pt (So, left shift results in hypoxemia and and it will develop polycythemia - that is the answer).
What I would like to know is if P50 for Hb were to be higher than normal, what condition would develop? I read somewhere that it's Anemia (high P50) but I can't figure out why.
Well if a patient with Hgb mutation causing a constitutive left shift is effectively chronically hypoxic due to decreased unloading, this stimulates epo production and the patient becomes polycythemic.
now just think of it in reverse. A Hgb mutation causing a constitutive right shift has the renal peritubular interstitial cells seeing chronically increased levels of oxygen compared to normal due to increased delivery in tissues. Hence those cells will down regulate epo production causing a low level anemia.
now just think of it in reverse. A Hgb mutation causing a constitutive right shift has the renal peritubular interstitial cells seeing chronically increased levels of oxygen compared to normal due to increased delivery in tissues. Hence those cells will down regulate epo production causing a low level anemia.
np theres more on high and low affinity hemglobing mutants here as well as an article on uptodate.
https://www.inkling.com/read/wintro...th/chapter-35/hemoglobins-with-altered-oxygen
https://www.inkling.com/read/wintro...th/chapter-35/hemoglobins-with-altered-oxygen
