Toward the end of a nitrogen washout test for functional residual ...

[burchfield96]

Toward the end of a nitrogen washout test for functional residual capacity, the expired concen-tration of N2 begins rising. What does this probably indicate?
 
  a. The patient is trying too hard.
  b. There is a leak in the system.
  c. The test is nearing completion.
  d. N2 is being trapped in the lungs.

Question 2

A patient has a vital capacity of 4200 ml, a functional residual capacity (FRC) of 3300 ml, and an expiratory reserve volume (ERV) of 1500 ml. What is the residual volume (RV)?
 
  a. 5700 ml
  b. 2700 ml
  c. 1800 ml
  d. 7500 ml

[joshraies]

Answer to Question 1

ANS: B
The test must occur in a leak proof circuit because the presence of any air increases the measured nitrogen percentages and results in grossly elevated measurements of lung volume.

Answer to Question 2

ANS: C
Once these corrections are made, the RV can be calculated by subtracting the ERV from the FRC according to the following equation: RV = FRC  ERV.

[burchfield96]

Thanks for the timely response, appreciate it

[strudel15]

Gracias!