Week 1 - mechanics and ventilation

Question 1

Why does air move into lungs?

Answer 1

negative pressure

Question 2

What forces do respiratory muscles need to overcome?

Answer 2

• elastic recoil from lungs and chest wall
• resistance to airflow
• inertia

Question 3

What is elastic recoil?

Answer 3

tendency for lungs to return to resting volume after distention

Question 4

What is compliance?

Answer 4

the ease with which the lung is expanded

-volume change per unit of pressure

Question 5

What are the factors that affect compliance?

Answer 5

lung volume, surfactant, pulmonary blood flow, age, disease

Question 6

What are the physiological advantages of surfactant?

Answer 6

• low surface tension - increased compliance
• decreased work of expanding lungs
• promotes stability of alveoli
• keeps alveoli dry

Question 7

Pulmonary blood flow - effects on compliance?

Answer 7

-increased capillary blood flow = decreased compliance

Question 8

Pulmonary odema effects on compliance?

Answer 8

large volume of alveoli - can’t expand

Question 9

Effect of age on compliance?

Answer 9

increased age = increased compliance

-loss of elasticity

Question 10

Effect of disease on compliance?

Answer 10

increased compliance = emphysema (elasticity)

-decreased compliance = fibrotic lung disease, collapsed alveoli, obesity

Question 11

What are the effects of altered compliance?

Answer 11

• diameter of airways = increased compliance - less elastic support, early airway closure, reduced airway diameter
• airflow = decreased compliance - decreased airflow, preferential ventilation of compliant lung units

Question 12

What is closing capacity?

Answer 12

lung vol at which some small airways begin to close

Question 13

What is closing volume?

Answer 13

closing capacity - RV

Question 14

What are factors affecting airflow resistance? (4)

Answer 14

• character of airway
• pattern of airflow
• density and viscosity
• lung volume

Question 15

Increased length of tube =

Answer 15

increased resistance

Question 16

Decreased diameter of tube =

Answer 16

increased resistance

Question 17

Where may airway narrowing occur?

Answer 17

• within airway lumen
• in lumen wall
• outside the airway

Question 18

Airway blockage in lumen

Answer 18

secretions or foreign materials

Question 19

Airway blockage in wall of lumen

Answer 19

hypertrophy of mucus glands, odema of bronchial walls, bronchospasm

Question 20

Airway blockage outside airways

Answer 20

loss of radial traction, tumour, local compression

Question 21

Increased gas viscosity =

Answer 21

increased resistance

Question 22

What is static hyperinflation?

Answer 22

always there ie emphysema

Question 23

What is dynamic hyperinflation?

Answer 23

compensatory (ie due to stress, chronic disease). High breathing rate = less expirattion = increased CO2 = airways remain open

Question 24

What are the causes of hypoxaemia?

Answer 24

• ventilation/perfusion mismatch
• hypoventilation
• diffusion abnormalities
• shunt

Question 25

Dead space

Answer 25

gas that does not take part in gas exchange

Question 26

Anatomic dead space?

Answer 26

volume of conducting airways

Question 27

Physiological dead space

Answer 27

volume of gas that does not eliminate carbon dioxide

Question 28

What is a dependent position?

Answer 28

area of lung that in in favour of gravity, ie closest to gravity
-increased compliance in dependent lung

Question 29

Factors affecting distribution of ventilation?

Answer 29

• weight of lung
• elastic properties of lung
• gravity
• intrapleural pressure gradient

Question 30

Factors affecting distribution of ventilation - wright of lung

Answer 30

-dependent portion more compressed = more compliant

Question 31

Factors affecting distribution of ventilation - intrapleural pressure gradient

Answer 31

more -ve at the top, less -ve in dependent regions

-greater -ve intrapleural pressure = greater distending pressure

Question 32

Factors affecting distribution of ventilation - elastic properties of lung

Answer 32

-upper (dependent) zone more stretched

Question 33

What happens when breathing at low lung volumes?

Answer 33

• preferential ventilation to upper zones
• lung not well expanded
• elastic recoil forces smaller
• intrapleural pressure in dependent zones less -ve than usual
• airway closure in dependent zones (intrapleural pressure in dependent zones now greater than airway pressure)

Question 34

What is perfusion?

Answer 34

blood flow of pulmonary circulation that is available for gas exchange

Question 35

What is shunt?

Answer 35

regions with low ratios (ie perfusion in excess to ventilation)
-blood which enters arterial system without passing through ventilated areas of lung