The Mechanics Of Breathing

Question 1

Why is the fall in alveolar pressure large enough to be observed?

Answer 1

There is a delay in pressure change as it takes time for the air to move

Question 2

What does impaired airway function lead to?

Answer 2

Insufficient ventilation

Question 3

What does the rate of airflow depend on?

Answer 3

The pressure gradient and level of airway resistance

Question 4

What happens to resistance as airway radius decreases?

Answer 4

Increases (and airflow decreases) massively

Question 5

What is airway resistance increased by (apart from small radius?)

Answer 5

Turbulent airflow

Question 6

What is patency?

Answer 6

State of being open (ie not collapsing/flat)

Question 7

What can cause airway obstruction?

Answer 7

Loss of airway patency due to degredation of structure

Question 8

What maintains patency in a healthy alveoli?

Answer 8

Elastin in surrounding alveoli provides radical traction to splint bronchioles against positive alveolar pressure

Question 9

What happens to the alveoli in COPD?

Answer 9

There is a reduction in radial traction, so the bronchioles collapse

Question 10

What does lung compliance quantise?

Answer 10

The relationship between the level of expansive force applied to the lung and the resulting change in lung volume

Question 11

What is trans pulmonary pressure?

Answer 11

The level of force acting to expand the lung

Question 12

What is trans pulmonary pressure made up of?

Answer 12

Alveolar pressure - intrapleural pressure

Question 13

How is lung compliance calculated?

Answer 13

By dividing a change in lung volume by the associated change in trans pulmonary pressure

Question 14

What is compliance expressed as on a graph?

Answer 14

The gradient

Question 15

What does it mean if there’s a steeper curve?

Answer 15

Greater level of lung compliance

Question 16

What does it mean if there’s a greater lung compliance?

Answer 16

Looser/easier to inflate lung

Question 17

What does a low lung compliance mean?

Answer 17

It’s stiffer/ harder to inflate the lung

Question 18

What factors affect lung compliance(3)?

Answer 18

Chest wall mechanics
Alveolar surface tension 
Elastin fibres (density)

Question 19

What diseases affect the chest wall mechanics?

Answer 19

Scoliosis
Muscular dystrophy
Obesity

Question 20

What disease affects the alveolar surface tension?

Answer 20

Neonatal respiratory distress syndrome

Question 21

What diseases affect the elastin fibre density?

Answer 21

Fibrosis (increases density)

COPD (decreases density)

Question 22

What do air-liquid interfaces generate?

Answer 22

Surface tension

Question 23

Why are alveoli lined with fluid?

Answer 23

To enable gas exchange

Question 24

What does laplaces law describe?

Answer 24

The pressure generated by the surface tension within a bubble

Question 25

What would happen if two different sized alveoli were connected via airways and what is this force overcome by?

Answer 25

Pressure gradients being created between the alveoli, resulting in smaller alveoli emptying into larger ones

Overcome by pulmonary surfactants

Question 26

What is a pulmonary surfactant?

Answer 26

Cocktail of different phospholipids and phospholipoproteins

Question 27

What are pulmonary surfactants secreted by?

Answer 27

Type two pneumocytes

Question 28

What do pulmonary surfactants do?

Answer 28

They disrupt the attractive forces and reduce surface tension (So lungs expand easier)

Also equalise pressure and volume across varying alveoli

Question 29

What happens to the concentration of pulmonary surfactant as the alveoli expand and why does it happen?

Answer 29

Decreases, which increase surface tension

Set amount of surfactant in each alveoli

Question 30

What does surfactant mean for the distribution of air in the alveoli?

Answer 30

Larger alveoli collapse into smaller ones

Question 31

How does surfactant prevent alveolar oedema?

Answer 31

• surface tension produced at the air-liquid interface reduces hydrostatic pressure. It is then pulled out of the surrounding capillaries into the alveoli

Question 32

What is neonatal respiratory distress syndrome caused by?

Answer 32

Insufficient production of pulmonary surfactant

Question 33

What is the pathway of neonatal respiratory distress syndrome?

Answer 33

Premature birth, maternal diabetes, congenital developmental issues

• > insufficient surfactant production
• > stiff lungs, alveolar collapse, oedema
• > respiratory failure
• > hypoxia

Question 34

Causes of death for neonatal respiratory distress syndrome

Answer 34

Pulmonary vasoconstriction, endothelial damage, acidosis, pulmonary + cerebral haemorrhage