Ventilation and Compliance

Question 1

Explain the difference between pulmonary ventilation and alveolar ventilation

Answer 1

pulmonary - total air movement in/out of lungs

alveolar - fresh at getting to alveoli and available for gas exchange

Question 2

What is anatomical dead space

Answer 2

volume of gas occupied by conducting airways, and therefore not available for gas exchange

Question 3

What causes the in vivo partial pressures of CO2/O2 to be different that those calculated theoretically

Answer 3

• residual volume dilutes pressures as it has already taken part in gas exchange
• water particles from humidification of inhaled air displaces some of the pressure

Question 4

What is surfactant and what cells produce it

Answer 4

• detergent like fliud

- type 2 alveolar cells

Question 5

What is the function of surfactant

Answer 5

reduces surface tension in alveolar surface membrane, reducing the tendency for it to collapse

Question 6

Why does surface tension arise on the alveolar surface

Answer 6

there is an air-water interface present; the attraction between water molecules

Question 7

Explain how surface tension arises

Answer 7

• thin fluid layer lining the membrane attracted to water vapour in gaseous form inside
• creates the air-water interface, causing inward force of water molecules
• causes alveolar collapse

Question 8

How does surfactant prevent this process

Answer 8

sits between water molecules and:

-prevents forces of attraction from developing
between them
- reduces inward pressure
- causes alveoli to remain open

Question 9

What is the overall benefit of surfactant production to breathing

Answer 9

• increases lung compliance
• reduces lung’s tendency to recoil
• makes work of breathing easier

Question 10

Why is surfactant more effective in smaller alveoli

Answer 10

molecules come closer together and are therefore more concentrated

Question 11

What is IRDS and how does it arise

Answer 11

• infant respiratory distress syndrome

- incomplete surfactant production in premature babies (doesn’t complete until week 36 of pregnancy)

Question 12

What makes it easier to breathe saline than air

Answer 12

there is no air-water interface to overcome in a saline solution

Question 13

What is compliance

Answer 13

a measure of the ability of the lungs to expand/contract relative to a given change in pressure

*stretchability, not elasticity

Question 14

What happens in lungs with high compliance

Answer 14

there is a large increase in lung volume relative to small changes in pressure

Question 15

What happens in lungs with low compliance

Answer 15

there is a small increase in lung volume relative to large changes in pressure

Question 16

Why is a greater decrease in pressure needed to reach a particular lung volume during inspiration as compared to expiration?

Answer 16

inspiration requires;

• overcoming surface tension
• overcoming tissue inertia

Question 17

Why is a greater increase in pressure needed to reach a particular lung volume during expiration as compared to inspiration?

Answer 17

expiration requires;

- overcoming resistance

Question 18

What happens to expiration in emphysema

Answer 18

it requires effort due to a loss of elastic tissue

Question 19

What happens to inspiration in fibrosis

Answer 19

it requires more effort due to the presence of inert fibrous tissue

Question 20

Explain the difference between volume changes at the base of the lung and the apex of the lung after the same given change in pressure (change in compliance)

Answer 20

base of the lung - can take in more volume for a given change in pressure as they are squashed by gravity

apex of the lung - can take in less volume for a given change in pressure as they remain slightly inflated and have not gravity squashing them

therefore compliance declines with height from base to apex

Question 21

How does alveolar ventilation change with height from base to apex

Answer 21

it declines

Question 22

What is the main symptom of an obstructive lung disorder

Answer 22

increased airway resistance (difficulty on expiration)

Question 23

Give two examples of obstructive lung disorders

Answer 23

• asthma

- COPD

Question 24

What is the main symptom of a restrictive lung disorder

Answer 24

loss of lung compliance (difficulty on inspiration)

• lung stiffness
• incomplete expansion

Question 25

Name two types of spirometry measurement

Answer 25

Static (volume exhaled)

Dynamic (time taken to exhale a certain volume)

Question 26

What volumes can be measured directly by spirometry

Answer 26

all volumes besides those with residual volumes (RV, TLC and FRC)

Question 27

What is FEV

Answer 27

forced expiratory volume

Question 28

What is FVC

Answer 28

forced vital capacity

Question 29

What should be observed in the FEV/FVC ratio in an obstructive lung disorder

Answer 29

A lower FEV value and an overall lower ratio

problems getting air out

Question 30

What should be observed in the FEV/FVC ratio in a restrictive lung disorder

Answer 30

Lower values for both measurements but an apparently normal/slightly elevated ratio
(problems getting air in, meaning less can come out)