changes in PaCO2 in case of exercise - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
USMLE Articles
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

Thread Tools Search this Thread Display Modes
Old 08-20-2011
USMLE Forums Guru
Steps History: 1+CK+CS
Posts: 460
Threads: 278
Thanked 160 Times in 79 Posts
Reputation: 170
Question changes in PaCO2 in case of exercise

Hi all:

I have a question. In case of exercise, we HYPERventilate in order to meet increased oxygen demand, so why in " FA 2011 p. 509 Respose to exercise "

it says that no change in PaCO2?? Since PACO2 is proportional to PaCO2 and PACO2 is inverse proportional to ventilation, then as we HYPERVENTILATE, we should have low PACO2 and PaCO2, right?

Please help me explain why it is no change in FA, thank you.
Reply With Quote Quick reply to this message

Old 08-21-2011
mayursn39's Avatar
USMLE Forums Addict
Steps History: 1+CK+CS
Posts: 193
Threads: 20
Thanked 506 Times in 99 Posts
Reputation: 516

PACO2=CO2 production/alveolar ventilation.
So though we hyperventilate the amount of CO2 production is also increasing leading to constant to PACO2.
Hope this helps
Reply With Quote Quick reply to this message
The above post was thanked by:
chienpolska (08-21-2011)
Old 08-21-2011
tootsie's Avatar
USMLE Forums Guru
Steps History: Not yet
Posts: 433
Threads: 16
Thanked 283 Times in 199 Posts
Reputation: 293
Show Teeth

During exercise, there is an increase in ventilatory rate (to supply body's demand for oxygen) that matches the increase in O2 consumption and CO2 production by the body. The stimulus for increased ventilation rate is not completely understood. It is still a mystery how the ventilation can be altered so precisely to meet the increase demand when these parameters seem to remain constant in the blood. Maybe chemoreceptors (when PaCO2 elevates) or mechanoreceptors in joints have something to do with it.

Hope this also helps.
Reply With Quote Quick reply to this message


Physiology-, Respiratory-

Quick Reply

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:
Please enter a password for your user account. Note that passwords are case-sensitive.
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.
Where you live. Leave blank if you don't want to tell.


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
Exercise and Cardiac Output! evavar USMLE Step 1 Forum 2 06-24-2011 08:24 AM
End Diastolic Volume in Exercise? xxmcstu USMLE Step 1 Forum 1 08-21-2010 08:03 PM
60 Minutes After Exercise Yerdini USMLE Step 1 Forum 2 09-27-2009 12:05 PM
PAO2 effect on PACO2! flex USMLE Step 1 Forum 2 08-15-2009 12:22 PM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2016 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)