5.6 Principles of Pulmonary Function Testing (PFT)

Question 1

List some things that PFTs can measure

Answer 1

• Lung mechanics
• Diffusion properties
• Actions of different stimuli

Question 2

List some situations where PFTs are used

Answer 2

• Assessing response to treatment
• Diagnosis and/or monitoring of respiratory disease
• Pre-operative and functional assessments

Question 3

How are predicted values for PFTs found?

Answer 3

Testing a large volume of patients; normal distribution

Question 4

What is meant by the lower limit of the normal (LLN) in terms of predicted values?

Answer 4

Lower limit of the normal is the bottom 5%

Question 5

What is the upper limit of the normal?

Answer 5

Top 5%

Question 6

Why is the LLN better than a fixed value?

Answer 6

Takes into account anthropometric characteristics

Question 7

What is the most common lung function test?

Answer 7

Spirometry

Question 8

Describe spirometry

Answer 8

• Clip nose
• Fill lungs completely
• BLAST air out
• repeat 3-8 times (or until repeatable and reliable results)
• Bronchodilator given
• Tested again

Question 9

How long does spirometry take?

Answer 9

20 minutes

Question 10

How does spirometry measure the amount of air left in the lungs after expiration?

Answer 10

It doesn’t

Question 11

Obstructive vs restrictive lung disease

Answer 11

Obstructive: Hard to exhale all air in lungs
Restrictive: hard to fully expand your lungs with air

Question 12

Does FEV1 increase or decrease during obstructive lung defect? Why?

Answer 12

• It decreases
• It becomes harder for air to move out of the lungs as quickly, so the amount of air that leaves in 1 second decreases

Question 13

Effect of obstructive ventilatory defect on FEV1/FVC ratio (relative to LLN)

Answer 13

• Decreased
• Takes longer to empty lungs and reach FVC

Question 14

What does obstructive lung disease look like on a flow volume loop?

Answer 14

• “Scooped out” downward slope

Question 15

Findings of restrictive ventilatory defect on flow volume loop/spirometry testing

Answer 15

• Near normal FEV1
• Normal or slightly elevated FEV1/FVC
• Usually, lower forced expiratory time

Question 16

List some examples of obstructive ventilatory defects

Answer 16

• Asthma
• Chronic bronchitis
• Emphysema

Question 17

List some examples of restrictive ventilatory defects

Answer 17

• Pleural effusion
• Congestion
• Fibrosis

(anything that pushes in on the lungs)

Question 18

Why is bronchodilator response significant in obstructive disorders? Give some examples to support your answer. What is the threshold for a significant response?

Answer 18

• Because they indicate whether or not the pathology can be reversed
• Conditions such as asthma are reversible
• Conditions such as COPD and emphysema aren’t

Threshold for significant response is 10% improvement.

Question 19

Does decreased FEV1/FVC indicate obstructive or restrictive lung disease?

Answer 19

It indicates obstructive; there is an airflow limitation, meaning air is not getting out fast enough (therefore obstructive)

Question 20

Does decreased FVC indicate obstructive or restrictive lung disease? Is this always the case, and why?

Answer 20

• Can indicate restrictive disease (lungs can’t expand as much, so total amount of exhaled air decreases)
• Might not be the case: maybe there is air left in the lungs, which would indicate something else. Confirm by measuring total lung capacity.

Question 21

Functional residual capacity

Answer 21

From end of quiet tidal breath to no more air in lungs at all (ERV + RV)

Question 22

Inspiratory capacity

Answer 22

Point from end of tidal volume (expiration) to maximum inspiratory capacity (VT + IRC)

Question 23

Explain how lung volume by helium dilution works

Answer 23

Uses boyles law: C1V1 = C2V2

• Create closed system (C1 and V1)
• Get patient to breathe in an out helium gas, and measure conc (gives C2)
• Use values to calculate V2., which is total lung capacity

Question 24

What happens to residual volume as we age? Why?

Answer 24

• It increases
• We lose elastic tissue and it becomes harder to empty our lungs

Question 25

Why does TLC increase in emphysema?

Answer 25

• Lungs are overstretched, like the elastic in a pair of old underpants
• As a result, TLC increases

Question 26

Describe changes in lung capacities in someone with pulmonary fibrosis

Answer 26

• Everything decreases
• It is harder to expand the lungs, but it is also harder to empty them, since elastic recoil is reduced

Question 27

Describe changes in lung capacities in someone with neuromuscular disease

Answer 27

• Decreased volume
• Increased reserve volume -> muscles are not working properly

Question 28

What is the probability that a healthy patient will have a lung function value below the lower limit of the normal?

Answer 28

5%; therefore, there is some lenience

Question 29

Does a normal lung function value always imply no disease? What are the implications of this?

Answer 29

• Not always
• Clinical examination remains really important

Question 30

Relationship between tissue area and rate of diffusion

Answer 30

Proportional

Question 31

Relationship between diffusion constant and rate of diffusion

Answer 31

Proportional

Question 32

Relationship between partial pressure across tissue barrier and rate of diffusion

Answer 32

Proportional

Question 33

Relationship between tissue thickness and rate of diffusion

Answer 33

Inversely proportional

Question 34

Explain how DLCO tests work

Answer 34

• Inhale tracer gas
• Inhaled CO
• Inhale regular air in the mixture
• The less CO left in the exhalation, the better the lungs are working, since the haemoglobin has taken up CO quickly

Question 35

Factors that will increase diffusing capacity of CO

Answer 35

• Increased Hb binding sites
• Increase amount of blood in pulmonary capillaries

Question 36

Factors that will decrease diffusing capacity of CO

Answer 36

• Decreased ability of CO to bind to Hb
• Reduces ability of CO to cross the air-blood barrier
• Reduces the amount of blood in the pulmonary capillaries