Lung Volumes Question - USMLE Forums
 USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
 Home USMLE Articles USMLE News USMLE Polls USMLE Books USMLE Apps
 USMLE Forums Lung Volumes Question
 Register FAQs Members List Search Today's Posts Mark Forums Read

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

#1
05-24-2011
 USMLE Forums Addict Steps History: 1+CK+CS+3 Posts: 186 Threads: 61 Thanked 259 Times in 66 Posts Reputation: 269
Lung Volumes Question

A middle aged man undergoes lung volume studies using helium dilution method. The Helium volume in the spirometer remains constant at 4L during the study. Patients vital capacity is 5L and ERV is 3L. The initial fraction of helium in the spirometer is 0.04 and after equilibrium in the lungs it is 0.02. The RV is approximately??

a) 2L
b) 1L
c) 1.5L
d) 0.5L
e) 2.5L

#2
05-24-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,378 Threads: 194 Thanked 3,255 Times in 881 Posts Reputation: 3265

b) 1L
#3
05-24-2011
 USMLE Forums Master Steps History: 1 + CK Posts: 630 Threads: 62 Thanked 287 Times in 186 Posts Reputation: 297

my ans is 1L
#4
05-24-2011
 USMLE Forums Scout Steps History: Not yet Posts: 26 Threads: 4 Thanked 3 Times in 3 Posts Reputation: 13
how

Quote:
 Originally Posted by bebix my answer is b) 1L
#5
05-24-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,378 Threads: 194 Thanked 3,255 Times in 881 Posts Reputation: 3265

Quote:
 Originally Posted by vikash how?? please explain
C1*V1 = C2*V2

where:
V1 = Volume of gas in spirometer.
V2 = Total gas volume ( FRC + volume of spirometer).
C1 = Initial (known) Helium Concentration.
C2 = Final Helium concentration (Measured by the spirometer).

C1*V1 = C2*(V1+FRC)

FRC = V1*(C1-C2)/C2
FRC = 4*(0.02)/0.02
FRC = 4L

FRC =ERV + RV
RV = 1L
 The above post was thanked by: Chemole (06-03-2011), oti nogonno (06-16-2011), prepink (06-30-2011), vikash (05-25-2011)
#6
05-24-2011
 USMLE Forums Scout Steps History: Not yet Posts: 14 Threads: 1 Thanked 3 Times in 3 Posts Reputation: 13

)): good one .....

Last edited by amritdhillon257; 05-24-2011 at 02:03 PM.
#7
05-25-2011
 USMLE Forums Scout Steps History: Not yet Posts: 26 Threads: 4 Thanked 3 Times in 3 Posts Reputation: 13

Quote:
 Originally Posted by bebix C1*V1 = C2*V2 where: V1 = Volume of gas in spirometer. V2 = Total gas volume ( FRC + volume of spirometer). C1 = Initial (known) Helium Concentration. C2 = Final Helium concentration (Measured by the spirometer). C1*V1 = C2*(V1+FRC) FRC = V1*(C1-C2)/C2 FRC = 4*(0.02)/0.02 FRC = 4L FRC =ERV + RV RV = 1L
where can i read this in detail? any book?
#8
05-25-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,378 Threads: 194 Thanked 3,255 Times in 881 Posts Reputation: 3265

Medical physiology: principles for clinical medicine

The book is not THAT good, but that concept is well explained

 The above post was thanked by: Chemole (06-03-2011)
#9
12-23-2012
 USMLE Forums Guru Steps History: Not yet Posts: 316 Threads: 115 Thanked 153 Times in 83 Posts Reputation: 163

i read through this yesterday, but there isn't an equation for this in costanzo or kaplan. is this high yield? would i find it in uworld?
#10
02-15-2013
 USMLE Forums Scout Steps History: Not yet Posts: 18 Threads: 0 Thanked 1 Time in 1 Post Reputation: 11

this formula is not in kaplan ,but this in dr najeeb lecture.

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

Message:
Options

## Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
User Name:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
 AMG IMG ---
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.

 Not yet Step 1 Only CK Only CS Only 1 + CK 1 + CS 1+CK+CS CK+CS 1+CK+CS+3 ---
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.