Pulmonary Function Testing

Question 1

Spirometry variable summary

Answer 1

Question 2

Expiratory Reserve Volume

Answer 2

the difference in volume between FRC and RV. It is altered by anything that changes FRC or RV

Question 3

Inspiratory Capacity

Answer 3

the difference in volume between FRC and TLC. It is altered by anything that changes either TLC or FRC

Question 4

FEV1

Answer 4

the volume of air exhaled from TLC during the first second of a forced (as hard and fast as possible) expiratory maneuver. Determined by driving pressure (recoil forces of lung and chest wall; expiratory muscle strength) and airway resistance.

Question 5

FEF25-75%

Answer 5

Forced Expiratory Flow between 25-75% of the vital capacity

Average expired flow over the middle half of the FVC maneuver and is regarded as a more sensitive measure of small airways narrowing than FEV1. Unfortunately, FEF25-75% has a wide range of normality, is less reproducible than FEV1, and is difficult to interpret if the VC (or FVC) is reduced or increased.

Question 6

FEV1/FVC ratio

Answer 6

FEV1 is a flow (volume/time); FVC is a volume. If an individual has increased airway resistance (all other things being normal), the FEV1 will be reduced, but the TLC and RV may be normal (which will result in a normal vital capacity). Thus, the FEV1/FVC ratio, when reduced, is indicative of increased expiratory airway resistance.

For this course, we will consider an FEV1/FVC ratio greater than 70% to be normal

Question 7

Low FEV1/FVC ratio can be interpreted as

Answer 7

Increased flow resistance on inspiration

Question 8

If FEV1/FVC ratio is normal, but the individual is clearly having trouble breathing, it may be the case that. . .

Answer 8

FEV1 and FVC are both reduced.

The ratio can remain normal or even higher than usual; this can be an indicator that the TLC is low and that the individual has an abnormality of the lung associated with increased recoil forces (e.g., interstitial lung disease about which you will learn in the coming weeks).

Question 9

The factors considered in determining “normal” predicted values

Answer 9

1. Distribution in a normal population – wide variation
2. . Age – changes in compliance of the lung and chest wall (lung more compliant with age, chest wall less compliant). There is natural decline in FEV1/FVC with age.
3. Sex – body proportions different between genders (larger thorax in men than women for same height…although this correction is also disputed by some.)
4. Race/Ethnicity – Standard equations to generate normal ranges for pulmonary function have “corrections” for race/ethnicity. The normal values for healthy African Americans are lower than for healthy Caucasians and Mexican Americans.

Question 10

Why do we see ‘barrel chests’ in patients with COPD?

Answer 10

Because the elastic recoil of the lung is impaired, meaning that the equilibrium between pulmonary elastic recoil and the elastic recoil of the chest wall is shifted. Since this equilibrium determines functional respiratory capacity, FRC is similarly shifted, and the lungs take up more volume at baseline. Hence, barrel chest.

Question 11

‘Buckets’ of pulmonary disease

Answer 11

Question 12

Categories of pulmonary test

Answer 12

1. Lung volume tests (TLC, FRC, etc)
2. Spirometry (how fast can you get air in/out)
3. Diffusing capacity of carbon monoxide (efficiency of oxygenation)
4. Arterial blood gas
5. 6-minute-walk test

Question 13

Why do we get such quick exhalation in the first second of FEV?

Answer 13

Because that air is coming from the large airways, and there is less resistance to pushing it out. Also, the recoil of our lung is highest at high lung volumes. And, lastly, the airways are least compressed, so even those mid-sized airways that contribute the bulk of resistance aren’t contributing as much resistance as they do later in exhalation.

Question 14

“Coving”

Answer 14

Divet into the effort independent portion of the exhalatory flow/volume curve. Due to obstructions in the small airways.

Question 15

FEV1 is a function measure for. . .

Answer 15

. . . small airways

Question 16

Obstructive lung diseases tend to have . . .

Answer 16

a low FEV1, but a normal FVC.

Typically FEV1/FVC < 0.7 for COPD

Question 17

Restrictive lung diseases tend to have. . .

Answer 17

a high or normal FEV1, but a low FVC.

Typically FEV1/FVC > 0.7

Question 18

When we breathe in, what happens to the size of our airways?

Answer 18

Our intra-thoracic airways become larger,

But our extra-thoracic airways become smaller.

Question 19

Intuitively, obstructions manifest themselves the most in our breathing cycle when. . .

Answer 19

. . . we are at the stage in our breathing cycle where the host airway is the most constricted.

Question 20

A patient has pulmonary function tests that show a normal total lung capacity (TLC), reduced forced vital capacity (FVC), normal functional residual capacity (FRC), and elevated residual volume (RV). This patient’s problem is most likely the consequence of:

Answer 20

Increased airway resistance

The normal TLC and FRC tell you that the compliance of the lung is likely normal. The vital capacity is down because the RV is elevated. When airway resistance is elevated, flow is reduced and the patient may not be able to exhale all the way to RV before having to stop and take a deep breath, which causes the RV to be larger than normal.

Question 21

As we age, the elastic properties of the lung tissue diminish, leading to increased compliance of the lung, and the chest wall becomes less compliant (resists deformation from its resting position). As a consequence, you would predict to find which of the following changes in pulmonary function tests in a healthy 65 year old compared to the same person at age 25.

Answer 21

residual volume will be bigger

Question 22

You are about to see a patient who has developed a scarring condition of his lung as a consequence of being treated with the drug bleomycin for cancer. The patient has developed shortness of breath and states that it feels as if he must work harder to get a deep breath. You are about to obtain pulmonary function tests and predict the results will show:

Answer 22

Low functional residual capacity

Question 23

Though intra-‘racial’ diversity is greater than inter-‘racial’ diversity, on average, the African-American population has ____ relative to European-Americans

Answer 23

Though intra-‘racial’ diversity is greater than inter-‘racial’ diversity, on average, the African-American population has lower TLC and FRC relative to European-Americans

Question 24

DLCO

Answer 24

Diffusing capacity of carbon monoxide

Patients breathe very low-dose CO and holds breath for 10 seconds. The difference between the amount of CO inhaled vs exhaled is measured. This is compared to an age-stratified reference range. >80% of average is normal. Then compare to ventilation.

This can tell us what the total alveolar surface area is

Question 25

Intrinsically low DLCO

Answer 25

• Pulmonary fibrosis
• Emphysema
• etc

Question 26

Extrinsically low DLCO

Answer 26

• Not a deep enough breath
• Obesity
• Chest wall deformity

Things that prevent people from taking a deep breath.

Question 27

Hemogolbin-related low DLCO

Answer 27

• Anemia

Question 28

Hemoglobin-related high DLCO

Answer 28

• Pulmonary hemorrhage
• Pulmonary edema
• Bronchitis/asthma
• Polycythemia (elevated hematocrit)

Question 29

Is there a diffusion problem?

DLCO: 80% predicted

Ventilation: 4L/5L

Answer 29

No

80% ventilation predicts 80% DLCO

Question 30

Is there a diffusion problem?

DLCO: 65% predicted

Ventilation: 4.5L / 5L

Answer 30

Yes!!! DLCO is lower than would be predicted by 90% ventilation.

Question 31

Summary of the relationship between obesity and pulmonary function

Answer 31

• Compliance curve shifted right (baseline pressure needed to get movement is higher, but otherwise curve unaffected. Just takes more ‘work’ to get things moving)
• RV is normal (competing chest weight and pleural pressure increase average to zero)
• TLC -
• FRC —

Question 32

Patients who are more flow limited will have a ___ residual volume and a ___ functional residual capacity.

Answer 32

Patients who are more flow limited will have a greater residual volume and a unchanged functional residual capacity.

However, they will likely end breathing above their functional residual capacity at the end expiratory lung volume.

Question 33

Pulmonary function testing summary

Answer 33

Question 34

A decrease in total lung capacity (TLC) generally indicates the presence of a ___

Answer 34

A decrease in total lung capacity (TLC) generally indicates the presence of a restrictive pattern

Question 35

If lung volumes (TLC, FRC, RV, etc) are reduced in a restrictive pattern symmetrically, . . .

Answer 35

. . . this suggests interstitial lung disease as the cause of the restrictive pattern. A low diffusing capacity also supports the diagnosis of interstitial lung disease as the cause of the restrictive pattern

Question 36

Restrictive pattern with a relatively preserved RV and a normal diffusing capacity suggest. . .

Answer 36

. . . neuromuscular or chest wall disease

Poor effort from the patient may also create this type of pattern

Question 37

A decrease in the ratio of forced expiratory volume in 1 second to forced vital capacity (FEV1/FVC) indicates ___

Answer 37

A decrease in the ratio of forced expiratory volume in 1 second to forced vital capacity (FEV1/FVC) indicates obstruction

Question 38

If FEV1 and FVC are reduced symmetrically. . .

Answer 38

. . . clues to the presence of obstructive disease in this setting are a low forced expiratory flow from 25% to 75% of vital capacity (FEF25%-75%), a normal to high TLC with a high ratio of RV to TLC, and the configuration of the flow-volume curve.

Question 39

Interpreting maximal midexpiratory flow

Answer 39

aka FEF25%-75%

More variable than most lung metrics. When lung volumes are low, FEF25%-75% can also be decreased without necessarily indicating coexisting airflow obstruction. Outside of these cases, FEF25%-75% may be a relatively sensitive measurement for airway obstruction.

An isolated abnormality in FEF25%-75% has sometimes been considered a marker for early or very mild airflow obstruction, theoretically reflecting “small airway disease.”

Question 40

Interpretation of diffusing capacity of the lung for carbon monoxide (DLCO)

Answer 40

• Make sure it has been adjusted for hemoglobin first!!!
• A decrease in the diffusing capacity reflects disease affecting the alveolar-capillary membrane or a decrease in pulmonary capillary blood volume
• An increase in the diffusing capacity can reflect increased pulmonary capillary blood volume or erythrocytes within alveolar spaces (pulmonary hemorrhage).

Question 41

Interpretation of the flow-volume curve

Answer 41

• An obstructive pattern is reflected by decreased flow relative to lung volume, generally accompanied by a “scooped out” or “coved” appearance to the descending part of the expiratory curve
• A restrictive pattern is characterized by decreased volumes and relatively preserved flow rates. The flow rates often appear increased relative to the small lung volumes, producing a tall, narrow curve.

Question 42

What is your broad diagnosis?

Answer 42

All measurements of lung volume (TLC, VC, FRC, RV) are significantly decreased, indicative of restrictive disease. FEV1 and FVC are decreased because of low lung volumes, but FEV1/FVC is preserved. This finding, along with the fact that FEF25%-75% is not decreased out of proportion to the decrease in lung volumes, indicates there is no obstruction. Diffusing capacity is decreased, suggesting that the restrictive disease is secondary to an abnormality of the pulmonary parenchyma rather than a result of chest wall or neuromuscular disease. The flow-volume curve is tall and narrow, consistent with a restrictive pattern. Diagnosis: Interstitial lung disease secondary to pulmonary sarcoidosis.

Question 43

What is your broad diagnosis?

Answer 43

FEV1 and FVC are both decreased. Because FEV1 is decreased more than FVC, FEV1/FVC is decreased. FEF25%-75% is also decreased. These values are indicative of obstructive lung disease. TLC is normal, and RV and FRC are increased. RV/TLC ratio is also increased. Therefore, there is no restriction, but the high RV/TLC ratio indicates there is “air trapping,” as is often expected with airflow obstruction. The diffusing capacity is decreased, reflecting loss of alveolar-capillary bed. The flow-volume curve shows an obstructive pattern characterized by a striking decrease in flow rates, well seen throughout most of the expiratory curve after the initial peak flow rate. This combination of significant airflow obstruction with normal or increased volumes and a low diffusing capacity suggests emphysema.

Question 44

What is your broad diagnosis?

Answer 44

TLC and FRC are reduced, indicating restrictive disease. RV is relatively preserved. FEV1 and FVC both are decreased, but FEV1/FVC ratio is preserved. There is no evidence for coexisting obstructive disease. Diffusing capacity is normal, suggesting the alveolar-capillary bed is preserved. The flow-volume curve is relatively tall and narrow, without any evidence of obstructive disease. Diagnosis: Restrictive pattern secondary to chest wall disease (kyphoscoliosis).