4. Compliance and Lung Function Tests

Question 1

What is surfactant?

Answer 1

Detergent like fluid produced by Type II alveolar cells

Question 2

What does surfactant do?

Answer 2

• Reduces surface tension on alveolar surface membrane thus reducing tendency for alveoli to collapse
• Increases lung compliance
• Reduces lung’s tendency to recoil
• Makes work of breathing easier

Question 3

Where does surface tension occur?

Answer 3

Where ever there is an air-water interface and refers to the attraction between water molecules

Question 4

Why is surfactant more effective in small alveoli than large alveoli?

Answer 4

Surfactant molecules come closer together and are therefore more concentrated

Question 5

When is surfactant produced?

Answer 5

Production starts at 25 weeks gestation and is complete by 36 weeks

Question 6

What stimulates surfactant production?

Answer 6

Thyroid hormones and cortisol which increase towards the end of pregnancy

Question 7

What can premature babies suffer from due to incomplete production of surfactant?

Answer 7

Infant Respiratory Distress Syndrome (IRDS)

Question 8

Why is there less change in pressure in a saline filled lung compared to lung inflation in utero?

Answer 8

There is no need to overcome surface tension as there is not= air-water interface

Question 9

Compliance

Answer 9

Change in volume relative to change in pressure

Question 10

What does compliance represent?

Answer 10

The stretchability of the lungs

Question 11

What does high compliance mean?

Answer 11

A large increase in lung volume for small decrease in ip pressure

Question 12

What does low compliance mean?

Answer 12

Small increase in lung volume for large decrease in ip pressure

Question 13

What can affect compliance?

Answer 13

• Disease states

- Age

Question 14

Why does expiration require effort in emphysema?

Answer 14

Loss of elastic tissue

Question 15

Why does inspiration require effort in fibrosis?

Answer 15

Inert fibrous tissue

Question 16

Why is expiration usually passive?

Answer 16

Normally effort (work) of inspiration is recovered as elastic recoil during expiration

Question 17

Why does the pressure volume curve vary between apex and base of the lung?

Answer 17

At the base, the volume change is greater for a given change in pressure

Question 18

Why does compliance decline with height from base to apex?

Answer 18

• The alveoli at the apex are more inflated due to FRC.
• At the base the alveoli are compressed between the weight of the lung above and the diaphragm below, hence more compliant on inspiration

Question 19

How does alveolar ventilation vary between apex and base?

Answer 19

Declines with height from base to apex

Question 20

What does a small change in ip pressure result in?

Answer 20

A larger change in volume at the base compared to the apex

Question 21

Obstructive Lung Disease

Answer 21

• Obstruction of air flow, especially on expiration

- Increased airway resistance

Question 22

Restrictive Lung Disease

Answer 22

Restriction of lung expansion

Question 23

What are 2 examples of obstructive lung disorders?

Answer 23

• Asthma

- COPD

Question 24

Chronic bronchitis

Answer 24

Inflammation of the bronchi

Question 25

Emphysema

Answer 25

Destruction of the alveoli, loss of elasticity

Question 26

What is the prevalence of COPD?

Answer 26

• 80 million people worldwide moderate to severe COPD

- Increases with age

Question 27

What are examples of restrictive lung disorders?

Answer 27

• Fibrosis
• Infant Respiratory Distress Syndrome
• Oedema
• Pneumothorax

Question 28

What is fibrosis?

Answer 28

Formation or development of excess fibrous connective tissue

Question 29

What are 2 causes of fibrosis?

Answer 29

• Idiopathic

- Asbestosis

Question 30

What are restrictive lung diseases cause by?

Answer 30

• Loss of lung compliance
• Lung stiffness
• Incomplete lung expansion

Question 31

Spirometry

Answer 31

Technique commonly used to measure lung function

Question 32

How can spirometry measurements be classed?

Answer 32

Static or dynamic

Question 33

Spirometry: Static

Answer 33

Where the only consideration made is the volume exhaled

Question 34

Spirometry: Dynamic

Answer 34

Where the time taken to exhale a certain volume is what is being measured

Question 35

What volumes can be measured directly by spirometry?

Answer 35

-Tidal volume
-Inspiratory reserve volume
-Expiratory reserve volume
Inspiratory capacity
Vital capacity

Question 36

What is the normal value for forced vital capacity?

Answer 36

5L

Question 37

What is the normal value for forced expiratory volume in 1 second?

Answer 37

4L

Question 38

What is the normal value for FEV1:FVC?

Answer 38

80%

Question 39

What is the value of FEV1:FVC for obstructive lung diseases?

Answer 39

42%

Question 40

What is the value of FEV1:FVC for restrictive lung disease?

Answer 40

90%

Question 41

Describe COPD

Answer 41

• Rate at which air is exhaled is much slower
• Total volume is also reduced
• Major effect is on airways and so FEV is reduced to a greater extent than FVC
• Ratio also reduced

Question 42

Describe pulmonary fibrosis.

Answer 42

• Absolute rate of airflow is reduced
• Total volume due to limitations to lung expansion
• Ratio remains constant or can increase as a large proportion of volume can be exhaled in the first second

Question 43

What limitations exist of the FEV1/FVC ratio?

Answer 43

• Obstructive, both FEV and FVC fall but FEV more so, so ratio is reduced
• Restrictive, both FEV and FVC fall so ratio remains much the same despite severe compromise of function
• Therefore normal FEV1/FVC ratio not always indicative of health

Question 44

What is the forced expiratory flow?

Answer 44

Average expired flow over the middle of an FVC

Question 45

How does FEV1 and FEF differ?

Answer 45

• FEF correlates with FEV1 but changes are generally more striking
• However, normal range is greater