Lung Testing A: Volumes & Capacities, Helium Dilution Flashcards
What is the definition of FRC?
Functional Residual Capacity
The volume of gas remaining in the lungs at end-expiratory level.
What is a typical FRC value?
2400 mL
What should you suspect if the FRC is high?
Obstructive disease may be present (air trapping)
What should you suspect if the FRC is low?
Restrictive disease may be present
What is the definition of RV?
Residual volume
The volume of gas in the lungs at the end of maximum expiration
What is the typical RV value?
1200 ml
What should you suspect if the RV is high?
Obstructive lung disease
What should you suspect if the RV is low?
Restrictive lung disease
What is the definition of TLC?
Total Lung Capacity
What is a typical TLC value?
6000 mL
What should you suspect if the TLC is high?
Obstructive lung disease
What should you suspect if the TLC is low?
Restrictive lung disease
What is the starting concentration of helium used in a helium dilution test?
10%
How long should the patient breathe diluted helium in a helium dilution test?
Up to 7 minutes.
With helium dilution, when should “switch in” occur?
At the end of normal expiration
When does “end of test” occur in helium dilution?
When helium concentration changes by less than 0.02% over a 30 second interval.
Helium dilution directly measures ___.
Basic spirometry measures ___.
The __ and the ___ is calculated.
FRC
ERV
RV and TLC
Helium dilution utilizes a ___ absorber and a ___ system.
CO2
Closed
In helium dilution, you have to subtract a small amount of volume to account for two things. What are they?
Helium absorbed by the blood
Dead space volume of the breathing valve
If you have to repeat the procedure in helium dilution, how long should you wait? Why?
10-15 min.
To allow helium to clear from the lungs and from the circuit.
In helium dilution, what are four reasons for erroneously high measurements?
- Switch-in occurred at a point before end expiration
- Eardrum rupture
- Analyzer failure
- Leak in circuit
Name two ways to detect a leak in the circuit in helium dilution.
- Erroneously high measurements
2. Failure to reach equilibrium
In helium dilution, if the patient’s breathing rate or volume increases, what does that indicate?
CO2 absorber is exhausted and should be replaced.
In helium dilution, if the cylinder pressure is below ___ psi, this indicates that the cylinder pressure is low and should be replaced.
50 psi
While doing helium dilution, the patient experiences visual changes (dimming of lights). What does this indicate? What are you going to do about it?
Hypoxemia
Check the gas concentration mixture
You’re doing helium dilution and it takes a really long time to reach equilibrium in a patient with normal lung function. What should you suspect?
Blower speed.
