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Old 02-07-2011
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Question Moving to high altitude respiratory physiology question

A healthy 50-year-old man who resides at sea level takes a 45-minute ride in a cable car from near sea level to a ski resort (altitude 3050 m). Which of the following best represents this patient 30 minutes after arrival at the resort?

Why the correct answer is C & not D?

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Old 02-07-2011
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Dont you hyperventilate at higher altitude? Does that not eliminate a lot of CO2 from your body? Wouldnt that increase your pH?

I am a terrible student, so I am probably wrong.
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Old 02-07-2011
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Why the [HCO3] should be high?
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Old 02-07-2011
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I recommend you read this
High Altitude Physiology
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Thank you I read it but I'm concerned about why the [HCO3] is high in the correct answer ?
in high altitude the Pco2 is low due to hyperventilation
& the [HCO3] is NORMAL cause the kidney start compensation after 2 days ,right?
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Quote:
Originally Posted by sona View Post
Thank you I read it but I'm concerned about why the [HCO3] is high in the correct answer ?
in high altitude the Pco2 is low due to hyperventilation
& the [HCO3] is NORMAL cause the kidney start compensation after 2 days ,right?
What are you talking about!!!!!!!!! Read the qn carefully, its says that the person came to the resort after 30mins skiing from the mountain. Bicarbs remain elevated for a few days before the kidney take action.
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Old 02-07-2011
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in kaplan physiology note
it says that in uncompensated respiratory alkalosis there will be a little decrease in HCO3 ....not even a normal ....
I can't understand why it's c not d
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Old 02-07-2011
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O I just went over this in Biochem. I will share what I learned.
1. There is an increase in respiration which will cause Respiratory Alkylosis.
2. There will be an early increase in P50 in Hb. Returns back to normal later.
3. Increase rate of glycolosis.
4. Increase Hb and Hematochrit.
correct me if I'm wrong.
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Old 02-07-2011
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Help I would also choose D!

I would also choose D!

aktorque is right that there would be no compensation yet, but even after reading all the posts, I would say that D is correct and the the answer key that sona is using is wrong.
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Old 02-07-2011
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I disagree

Quote:
Originally Posted by Mondoshawan View Post
I would also choose D!

aktorque is right that there would be no compensation yet, but even after reading all the posts, I would say that D is correct and the the answer key that sona is using is wrong.
Thank u for your answer
but i'm not saying c
I chose d & it was wrong ...
they say the correct answer is c & i'm asking why it's c not d ?
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Quote:
Originally Posted by angermngment View Post
Dont you hyperventilate at higher altitude? Does that not eliminate a lot of CO2 from your body? Wouldnt that increase your pH?
You are right - but normal isn't marked on that Davenport diagram. Normal bicarb is 24 and normal pH is 7.4 - I've put a green pepper on the original to show normal:



Quote:
Originally Posted by sona
I chose d & it was wrong ...
they say the correct answer is c & i'm asking why it's c not d ?
I really still think it's D, and that whoever keyed the answers to that test made a mistake. In acute respiratory alkalosis, you hyperventilate, blowing off CO2 - so your pCO2 goes down. Your bicarb also drops (that's the point of blowing off CO2, right?) by about 2 mEq per 10 mmHg drop in pCO2. That's totally choice D in that diagram. With C, bicarb is drastically raised. I might be missing something (I get mixed up on acid-base sometimes), but I can't see C being the correct answer here...
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Old 02-07-2011
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Key points regarding compensation in respiratory alkalosis:

Physicochemical effect: Initially there is an immediate physicochemical change which lowers the bicarbonate slightly.
Role of Kidney: The effector organ for compensation is the kidney.
Slow Response: The renal response has a slow onset and the maximal response takes 2 to 3 days to be achieved.
Outcome: The drop in bicarbonate results in the extracellular pH returning only partiallytowards its normal value.

Compensation in an ACUTE Respiratory Alkalosis

Mechanism:Changes in the physicochemical equilibrium occur due to the lowered pCO2 and this results in a slight decrease in HCO3-. There is insufficient time for the kidneys to respond so this is the only change in an acute respiratory alkalosis. The buffering is predominantly by protein and occurs intracellularly; this alters the equilibrium position of the bicarbonate system.
Magnitude: There is a drop in HCO3- by 2 mmol/l for every 10mmHg decrease in pCO2 from the reference value of 40mmHg.
Limit: The lower limit of 'compensation' for this process is 18mmol/l - so bicarbonate levels below that in an acute respiratory alkalosis indicate a co-existing metabolic acidosis. (Alternatively, their may be some renal compensation if the alkalosis has been present longer than realised.)

Hope this will help you a bit to understand the physio behind it.
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Old 02-08-2011
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Quote:
Originally Posted by Myticketout View Post
O I just went over this in Biochem. I will share what I learned.
1. There is an increase in respiration which will cause Respiratory Alkylosis.
2. There will be an early increase in P50 in Hb. Returns back to normal later.
3. Increase rate of glycolosis.
4. Increase Hb and Hematochrit.
Sorry. I meant initial decrease in P50 Hb. Later increase in 23BPG causes it to go back to normal later.
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  #14  
Old 09-17-2011
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this is a high yield question!

and the answer should be D
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