Hb Oxygen Dissociation Curve Question - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 06-13-2011
INCOGNITO's Avatar
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 343
Threads: 127
Thanked 525 Times in 192 Posts
Reputation: 535
Question Hb Oxygen Dissociation Curve Question

A 45 year old man was brought to ER after he was found nearly unconscious in his garage with his automobile running. Which of following is most likely to be decreased in this patient.

a) Arterial oxygen tension
b) Blood HB level
c) Heart Rate
d) P50 of Hb-dissociation curve
e) Respiratory Rate
Reply With Quote Quick reply to this message



  #2  
Old 06-13-2011
bebix's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,357
Threads: 194
Thanked 3,269 Times in 881 Posts
Reputation: 3279
Default

d)P50 of Hb-dissociation curve
Reply With Quote Quick reply to this message
  #3  
Old 06-13-2011
INCOGNITO's Avatar
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 343
Threads: 127
Thanked 525 Times in 192 Posts
Reputation: 535
Default

can u explain why its case of CO poisoning and some other curve detail plz
Reply With Quote Quick reply to this message
 
  #4  
Old 06-13-2011
bebix's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,357
Threads: 194
Thanked 3,269 Times in 881 Posts
Reputation: 3279
Default

because CO shift the curve to the left
Reply With Quote Quick reply to this message
  #5  
Old 06-13-2011
USMLE Forums Veteran
 
Steps History: 1 + CS
Posts: 216
Threads: 56
Thanked 116 Times in 56 Posts
Reputation: 116
Default

its CO poisoning b/c of Car running in the garage (we assume that the garage was closed).....another scenario is house fires but then you can have CO or cyanide poisoning b/c of upholstery etc!

CO competitively binds Hb against O2, CO has 200x more affinity for Hb than O2 does.....and PaO2 does not change its normal (dissolved in plasma), P50 of Hb changes b/c P50= saturation of 50% of Hb with O2.....since you have CO which is 200x more sticky to Hb than O2 it will displace O2 and "sit in its chair" on Hb.....thus you have to give 100% O2 to relieve the reversible competition by CO...

hope this helps
Reply With Quote Quick reply to this message
The above post was thanked by:
INCOGNITO (06-13-2011)
  #6  
Old 06-13-2011
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,175
Threads: 38
Thanked 854 Times in 478 Posts
Reputation: 864
Default

Yep, the answer is d)
Reply With Quote Quick reply to this message
  #7  
Old 06-14-2011
INCOGNITO's Avatar
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 343
Threads: 127
Thanked 525 Times in 192 Posts
Reputation: 535
Default

i understand whole Hb-dissocaition curve but WHAT IS p-50 of curve?
Reply With Quote Quick reply to this message
  #8  
Old 06-14-2011
bebix's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,357
Threads: 194
Thanked 3,269 Times in 881 Posts
Reputation: 3279
Smile

Quote:
Originally Posted by IKR123 View Post
i understand whole Hb-dissocaition curve but WHAT IS p-50 of curve?
The partial pressure of oxygen in the blood at which the haemoglobin is 50% saturated is known as the P50.

In the presence of disease or other conditions that change the haemoglobin's oxygen affinity and, consequently, shift the curve to the right or left, the P50 changes accordingly.

An increased P50 indicates a rightward shift of the standard curve, which means that a larger partial pressure is necessary to maintain a 50% oxygen saturation. This indicates a decreased affinity. Conversely, a lower P50 indicates a leftward shift and a higher affinity.

p50.bmp
Reply With Quote Quick reply to this message
The above post was thanked by:
1TA2B (06-14-2011), Hamada (07-15-2014), INCOGNITO (06-14-2011)
  #9  
Old 06-14-2011
INCOGNITO's Avatar
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 343
Threads: 127
Thanked 525 Times in 192 Posts
Reputation: 535
Default

bundle of thanks
Reply With Quote Quick reply to this message
  #10  
Old 06-14-2011
1TA2B's Avatar
USMLE Forums Guru
 
Steps History: CK Only
Posts: 475
Threads: 39
Thanked 353 Times in 169 Posts
Reputation: 376
Default

Quote:
Originally Posted by bebix View Post
The partial pressure of oxygen in the blood at which the haemoglobin is 50% saturated is known as the P50.

In the presence of disease or other conditions that change the haemoglobin's oxygen affinity and, consequently, shift the curve to the right or left, the P50 changes accordingly.

An increased P50 indicates a rightward shift of the standard curve, which means that a larger partial pressure is necessary to maintain a 50% oxygen saturation. This indicates a decreased affinity. Conversely, a lower P50 indicates a leftward shift and a higher affinity.

Attachment 1518
Yes I agree that CO has higher affinity to bind HB. So in CO toxication, Hb's affinity to bind O2 is decreased and so the P50 should move to the right? Not - left as you mentioned earlier?
__________________
Skill+Hardwork+Preparation=Success
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Reply With Quote Quick reply to this message
The above post was thanked by:
INCOGNITO (06-14-2011)
  #11  
Old 06-14-2011
bebix's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,357
Threads: 194
Thanked 3,269 Times in 881 Posts
Reputation: 3279
Default

Quote:
Originally Posted by 1TA2B View Post
Yes I agree that CO has higher affinity to bind HB. So in CO toxication, Hb's affinity to bind O2 is decreased and so the P50 should move to the right? Not - left as you mentioned earlier?
remember:
CO, HbF, low T....(and others) => curve shift to the left => dec. p50

"An increased P50 indicates a rightward shift of the standard curve, which means that a larger partial pressure is necessary to maintain a 50% oxygen saturation. This indicates a decreased affinity. Conversely, a lower P50 indicates a leftward shift and a higher affinity."
Reply With Quote Quick reply to this message
  #12  
Old 06-14-2011
bebix's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,357
Threads: 194
Thanked 3,269 Times in 881 Posts
Reputation: 3279
Smile

CO competes for O2 binding sites on Hb => binding of CO to Hb INCREASES the affinity of remaining sites for O2 => causing a shift of the curve to the left
Reply With Quote Quick reply to this message
The above post was thanked by:
NAZIAMK (12-23-2011)
  #13  
Old 06-14-2011
1TA2B's Avatar
USMLE Forums Guru
 
Steps History: CK Only
Posts: 475
Threads: 39
Thanked 353 Times in 169 Posts
Reputation: 376
Default

Quote:
Originally Posted by bebix View Post
CO competes for O2 binding sites on Hb => binding of CO to Hb INCREASES the affinity of remaining sites for O2 => causing a shift of the curve to the left
I got it. Thanks.

It makes sense now-CO2 and O2 competing against each other for Hb!
__________________
Skill+Hardwork+Preparation=Success
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Reply With Quote Quick reply to this message



Reply

Tags
Cardiovascular-, Physiology-, Respiratory-, Step-1-Questions, Toxicology-

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Biostatistics #10 - Normal curve 2 bebix USMLE Step 1 Forum 13 06-19-2011 04:22 AM
Oxygen Dissociation Curve for Carbon Monoxide and MetHemoglobin Jackstraw1589 USMLE Step 1 Forum 5 05-26-2011 12:16 AM
Mixed Venous Oxygen Content apx85 USMLE Step 1 Forum 1 05-25-2011 02:01 PM
Oxygen dissociation curve to the left or to the right? devareddy USMLE Step 1 Forum 6 07-27-2010 06:18 AM
Hemoglobin Dissociation Curve Sabio USMLE Step 1 Mnemonics 4 07-26-2010 08:25 AM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)