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USMLE Step 1 Bits & Pieces High yield short focused points, monographs, charts, illustrations, tables, and other stuff related to the USMLE Step 1 Exam.


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  #1  
Old 08-16-2009
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Lungs High Altitude Physiology

This is commonly tested in step 1

  • At high altitudes there's less oxygen in air so the first effect is hypoxia and decreased dissolved oxygen in the blood.
  • The immediate response will be stimulation of peripheral chemoreceptors which in turn in send signals to respiratory drives to breath more.
  • So hyperventilation develops which in turn leads to Respiratory Alkalosis.
  • Respiratory alkalosis will shift the hemoglobin dissociation curve to the left so that Hb can pick up O2 easier.
  • The kidney will respond to alkalosis by generating hydrogen ions and this will correct the PH back to normal.
  • After 2-3 days the 2,3 Diphosphoglycerate level in RBC will increase and this will shift the Hb curve (this time) to the right making O2 delivery easier to tissues. (Athletes go to mountains before the olympics, so that when they return to sea level, they have a right shifted Hb curve and so easier O2 delivery to their muscles during their competitions).
  • Another change that start right away is the increase of eryrthopoietin secretion but this takes a week or so before we can see polycythemia and increased hematocrit level. These changes in turn will correct the dropped down oxygen content of the blood.
  • Note that no matter how long you stay in high altitudes the PAO2, PACO2, and Hemoglobin saturation will remain decreased as we breath less FIO2 and we continue to hyperventilate.

Last edited by Sabio; 01-25-2010 at 04:36 PM.
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  #2  
Old 08-24-2009
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Finally, I understood the Hb curve in high altitudes
Thanks for the great post
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Old 11-22-2009
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This paragraph will solve many USMLE Step 1 questions. Thanks
I was always confused, whether we have left or right shifted hemoglobin dissociation curve in high altitudes.
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  #4  
Old 01-13-2010
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Thank you soooo much , it was always diff for me
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Old 01-25-2010
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Default HCO3 should decrease as compensation(slow) not increase

Quote:
Originally Posted by Sabio View Post
This is commonly tested in step 1

  • At high altitudes there's less oxygen in air so the first effect is hypoxia and decreased dissolved oxygen in the blood.
  • The immediate response will be stimulation of peripheral chemoreceptors which in turn in send signals to respiratory drives to breath more.
  • So hyperventilation develops which in turn leads to Respiratory Alkalosis.
  • Respiratory alkalosis will shift the hemoglobin dissociation curve to the left so that Hb can pick up O2 easier.
  • The kidney will respond to alkalosis by generating bicarbonate and this will correct the PH back to normal.
  • After 2-3 days the 2,3 Diphosphoglycerate level in RBC will increase and this will shift the Hb curve (this time) to the right making O2 delivery easier to tissues. (Athletes go to mountains before the olympics, so that when they return to sea level, they have a right shifted Hb curve and so easier O2 delivery to their muscles during their competitions).
  • Another change that start right away is the increase of eryrthopoietin secretion but this takes a week or so before we can see polycythemia and increased hematocrit level. These changes in turn will correct the dropped down oxygen content of the blood.
  • Note that no matter how long you stay in high altitudes the PAO2, PACO2, and Hemoglobin saturation will remain decreased as we breath less FIO2 and we continue to hyperventilate.
initial respond to respiratory alkalosis is release of H from intracellular and extracellular, then followed by kidney's conservation of H, --->decreased HCO3
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  #6  
Old 01-25-2010
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Quote:
Originally Posted by jamestan View Post
initial respond to respiratory alkalosis is release of H from intracellular and extracellular, then followed by kidney's conservation of H, --->decreased HCO3
You are absolutely right thanks for the correction
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  #7  
Old 07-26-2010
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one question,

y then in books they dont show the curve shifting the left first then to the right? i think they should to make things clearer.
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Old 06-05-2014
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I think it is metabolic alkalosis, not respiratory?
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Acid-Base-, Physiology-, Respiratory-

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