Pulmonary Function Tests

Question 1

What are the two main types of respiratory disorders?

Answer 1

Obstructive and Restrictive

Question 2

What are restrictive disorders?

Answer 2

Extra-airway disorders which restrict the ability of the lungs to entirely fill with oxygen

Question 3

What are obstructive disorders?

Answer 3

Airways diseases which are associated with obstructed airflow

Question 4

What is FVC?

Answer 4

Forced vital capacity – the maximum amount of air which you can forcibly exhale from your lungs after fully inhaling

Question 5

On a flow volume loop, which direction is exhalation and which direction is inhalation?

Answer 5

Expiration = going up
Inspiration = going down

Question 6

How do you calculate the vital capacity from a flow volume loop?

Answer 6

The difference between the two x-intercepts

Question 7

What is the tidal volume?

Answer 7

The amount of air inhaled and exhaled per breath

Question 8

What is PEF?

Answer 8

• Peak expiratory flow – the maximum flow rate
• Taken by the peak of the flow loop

Question 9

What are four reasons which spirometric pulmonary function tests might be undertaken?

Answer 9

1. Evaluate symptoms eg breathlessness
2. Monitor the progression of a lung disease over time
3. Monitor the efficacy of the treatment
4. Use it as a screening tool in the absence of sympoms

Question 10

Describe how a flow volume loop would look for a patient with mild obstructive disease?

Answer 10

• Reduced FVC
• Indented exhalation curve (coving)
• Maximum flow rate decreases

Question 11

What are the major disadvantages of the spirometric pulmonary function tests?

Answer 11

Heavy reliance on technique and can be rather uncomfortable for patients which reduces their motivation to apply maximum effort

Question 12

What does a flow volume loop look like for a patient with severe obstructive disease?

Answer 12

• Reduced FVC
• Significantly indented exhalation curve (coving)
• Reduced peak expiratory flow

Question 13

What is a flow volume loop like for patients with a restrictive disease?

Answer 13

• Reduced FVC
• Narrow curve
• Normal gradient at start with slightly lower peak due to reduced stretch

Question 14

What is the flow volume loop like for someone with a variable extrathoracic obstruction?

Answer 14

Blunted inspiratory curve
Normal expiratory curve

Question 15

What is the flow volume loop like for someone with a variable intrathoracic obstruction?

Answer 15

Blunted expiratory curve
Normal inspiratory curve

Question 16

What is the flow volume loop like for someone with a fixed airway obstruction?

Answer 16

Blunted inspiratory cure
Blunted expiratory curve
Both at a matched rate

Question 17

How do work out the PEF from a flow volume loop?

Answer 17

Highest observed y value

Question 18

How to calculate the FEV1 from a spirometer pulmonary test?

Answer 18

Read the Y value from X=1 second

Question 19

How to calculate the Peak Expiratory Flow Rate on spirometer graph?

Answer 19

Read up from x = 0.2 seconds
Multiply by 300 for L/minute

Question 20

What does a spirometer curve look like in a obstructive disease?

Answer 20

Low peak expiratory flow
Reduced FEV1
Reduced FEV1/FVC ratio

Question 21

Why does an obstructive condition result in a shallow spirometery curve?

Answer 21

• Severe airflow limitation caused by narrowing of the medium and small airways
• Respiratory muscle weakness and increased lung compliance means inability to generate the pressure to clear lungs quickly, hence increasing residual volume

Question 22

Why might there be wavy airflow pattern after a certain period of time despite having normal airflow?

Answer 22

• Patients may be unable to hold the expiration further
• This is a manifestation of the Hering-Breuer reflex where afferent signals from the airways lead to simulation of inspiration and cessation of expiratory muscle force

Question 23

What are some causes of extra-pulmonary restrictive diseases?

Answer 23

Obesity, Pneumoconiosis, Pulmonary fibrosis and severe burns

Question 24

What does a spirometer curve look like in a restrictive disease?

Answer 24

FVC decreased
FEV1 nearly expels all air

Question 25

What are the spirometry results for restrictive disease?

Answer 25

FVC lower (lung capacity restricted)
FEV1 normal unless airways affected
Thus FEV1/FVC normal or slightly higher than 0.7

Question 26

What are the spirometry results for obstructive disease?

Answer 26

FEV1 < 80% of predicted value (can’t expel air quickly)
FVC is normal
FEV1/FVC < 0.7

Question 27

Why is the following spirometry trace unrealistic?

Answer 27

• Rate of inspiration and expiration shouldn’t be the same
• Should be a plateau towards end of inspiration/expiration, as more effort is required to breathe in/out the last 10-20% of air

Question 28

What does our body have to prevent airways collapsing?

Answer 28

Cartilaginous support in large extrapulmonary airways

Question 29

What word describes a positive transmural pressure?

Answer 29

Patent

Question 30

What word describes a negative transmural pressure?

Answer 30

Collapse

Question 31

During inspiration why does the alveolar pressure decrease?

Answer 31

The diaphgram contracts, thoracic cavity increases in volume and intra-alveolar pressure decreases

Question 32

During inspiration why does the pleural pressure decrease?

Answer 32

The adhesive force of the pleural fluid causes the lungs to expand along with the thoracic cavity, and the increase in volume of the pleural cavity decreases pleural pressure

Question 33

How does the transmural pressure change during inspiration?

Answer 33

It increases due to alveolar and pleural pressure decreasing

Question 34

Why does transmural pressure continue increasing towards end-inspiration?

Answer 34

During mid-inspiration, pleural pressure stays the same but alveolar pressure decreases due to gas exchange, so the difference between them increases

Question 35

During hard-expiration, why is there the chance that the airways collapse?

Answer 35

• Hard expiration causes both pleural and airway pressures to increase
• If pleural exceeds airway pressure at any point, air flow can be cut off, thus causing collapse