3. Surfactant, Compliance and lung function tests

Question 1

What type of cell makes up alveolar walls?

Answer 1

Thin walled “Type I” cells which permit gas exchange Specialised “Type II” cells which secrete surfactant fluid

Question 2

What is the function of surfactant?

Answer 2

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

Question 3

What is surface tension?

Answer 3

The attraction that occurs between water molecules that occurs whenever there is an air-water interface and refers to the attraction between water molecules.

Question 4

When is surfactant most effective?

Answer 4

In small alveoli than large alveoli because surfactant molecules come closer together and are therefore more concentrated.

Question 5

What force has to be overcome during inspiration?

Answer 5

Inward force caused by the elasticity of the lungs - they are stretched slightly open even at the end of a relaxed expiration - natural tendency to recoil (contract inwards)

Question 6

What type of alveoli has the greatest pressure?

Answer 6

The smallest ones

Question 7

When does surfactant production start? Finish?

Answer 7

25 weeks gestation Complete by 36 weeks

Question 8

What stimulates surfactant production?

Answer 8

Thyroid hormones and cortisol which increase towards the end of pregnancy

Question 9

Why is less change in pressure required to inflate lung in utero?

Answer 9

Don’t need to overcome surface tension (no-air water interface)

Question 10

What is meant by compliance?

Answer 10

Change in volume relative to change in pressure

Question 11

What is high compliance?

Answer 11

Large increase in lung volume for small decrease in ip (intrapleural) pressure

Question 12

What is low compliance?

Answer 12

Small increase in lung volume for large decrease in ip (intrapleural) pressure

Question 13

It requires a greater change in pressure (from FRC) to reach a particular lung volume during inspiration, than to maintain that volume during expiration Why?

Answer 13

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

Question 14

What is emphysema?

Answer 14

Toxins in smoke activate elastase causing loss of elastic tissue - means expiration requires effort

Question 15

What is fibrosis?

Answer 15

Inert fibrous tissue means effort of inspiration increases

Question 16

What is the law of LaPlace?

Answer 16

The pressure of alveolus = 2 times the surface tension divided by the radius

Question 17

Which part of the lung changes more significantly in volume when the pressure increases?

Answer 17

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

Question 18

What is the relationship between height from base to apex and compliance/alveolar ventilation?

Answer 18

Decrease as height increases

Question 19

Why does compliance decrease with height?

Answer 19

Alveoli at the apex are more inflated at FRC. At the base the alveoli are compressed between the weight of the lung above and the diaphragm below and hence more compliant on inspiration. Alveoli at the top are further inflated than the alveoli at the base of the lung for the duration of the breathing cycle - hence they are able to inflate less

Question 20

What is an obstructive lung disease?

Answer 20

Obstruction of air flow, especially on expiration

Question 21

What is restrictive lung disease?

Answer 21

Restriction of lung expansion

Question 22

What is transpulmonary pressure?

Answer 22

The relationship between the alveolar pressure and the intrapleural pressure - always positive.

Question 23

Give examples of obstructive lung disorders

Answer 23

Asthma COPD (chronic obstructive pulmonary disease)

Question 24

Give examples of restrictive lung disorders

Answer 24

Involve loss of lung compliance (lung stiffness, incomplete lung expansion) Fibrosis (formation or development of excess fibrous connective tissue Idiopathic (cause unknown); 1:100,00 per year Asbestosis (and other occupational origins e.g. coal dust) Infant Respiratory Distress Syndrome: (insufficient surfactant production) Oedema - fluid builds up around alveoli creating pressure which requires more force to inflate Pneumothorax

Question 25

What is used to measure lung function?

Answer 25

Spirometery

Question 26

What is a static measurement in spirometry?

Answer 26

Where the only consideration made is the volume exhaled

Question 27

What is a dynamic measurement in spirometry?

Answer 27

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

Question 28

What measurements can be measured directly by spirometery?

Answer 28

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

Question 29

What is the average FEV1 for a healthy male?

Answer 29

4 litres

Question 30

What is the forced vital capacity for a healthy male?

Answer 30

5 litres

Question 31

How do you calculate the FEV1/FVC?

Answer 31

Divide the forced expiratory volume in one second by the forced vital capacity

Question 32

What are the FEV and FVC for an obstructive respiratory disorder?

Answer 32

FEV decreases (significantly) FVC is also reduced FRC may be increased Ratio is reduced

Question 33

What are the FEV and FVC for an restrictive respiratory disorder?

Answer 33

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

Question 34

What is a forced expiratory flow?

Answer 34

Average expired flow over the middle of a forced vital capacity