Lung Testing A: Volumes & Capacities, Helium Dilution

Question 1

What is the definition of FRC?

Answer 1

Functional Residual Capacity

The volume of gas remaining in the lungs at end-expiratory level.

Question 2

What is a typical FRC value?

Answer 2

2400 mL

Question 3

What should you suspect if the FRC is high?

Answer 3

Obstructive disease may be present (air trapping)

Question 4

What should you suspect if the FRC is low?

Answer 4

Restrictive disease may be present

Question 5

What is the definition of RV?

Answer 5

Residual volume

The volume of gas in the lungs at the end of maximum expiration

Question 6

What is the typical RV value?

Answer 6

1200 ml

Question 7

What should you suspect if the RV is high?

Answer 7

Obstructive lung disease

Question 8

What should you suspect if the RV is low?

Answer 8

Restrictive lung disease

Question 9

What is the definition of TLC?

Answer 9

Total Lung Capacity

Question 10

What is a typical TLC value?

Answer 10

6000 mL

Question 11

What should you suspect if the TLC is high?

Answer 11

Obstructive lung disease

Question 12

What should you suspect if the TLC is low?

Answer 12

Restrictive lung disease

Question 13

What is the starting concentration of helium used in a helium dilution test?

Answer 13

10%

Question 14

How long should the patient breathe diluted helium in a helium dilution test?

Answer 14

Up to 7 minutes.

Question 15

With helium dilution, when should “switch in” occur?

Answer 15

At the end of normal expiration

Question 16

When does “end of test” occur in helium dilution?

Answer 16

When helium concentration changes by less than 0.02% over a 30 second interval.

Question 17

Helium dilution directly measures ___.
Basic spirometry measures ___.
The __ and the ___ is calculated.

Answer 17

FRC
ERV
RV and TLC

Question 18

Helium dilution utilizes a ___ absorber and a ___ system.

Answer 18

CO2

Closed

Question 19

In helium dilution, you have to subtract a small amount of volume to account for two things. What are they?

Answer 19

Helium absorbed by the blood

Dead space volume of the breathing valve

Question 20

If you have to repeat the procedure in helium dilution, how long should you wait? Why?

Answer 20

10-15 min.

To allow helium to clear from the lungs and from the circuit.

Question 21

In helium dilution, what are four reasons for erroneously high measurements?

Answer 21

1. Switch-in occurred at a point before end expiration
2. Eardrum rupture
3. Analyzer failure
4. Leak in circuit

Question 22

Name two ways to detect a leak in the circuit in helium dilution.

Answer 22

1. Erroneously high measurements

2. Failure to reach equilibrium

Question 23

In helium dilution, if the patient’s breathing rate or volume increases, what does that indicate?

Answer 23

CO2 absorber is exhausted and should be replaced.

Question 24

In helium dilution, if the cylinder pressure is below ___ psi, this indicates that the cylinder pressure is low and should be replaced.

Answer 24

50 psi

Question 25

While doing helium dilution, the patient experiences visual changes (dimming of lights). What does this indicate? What are you going to do about it?

Answer 25

Hypoxemia

Check the gas concentration mixture

Question 26

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?

Answer 26

Blower speed.