9.1 Mechanical properties of Lung and Chest Wall

Question 1

Where is airway flow the highest?

Answer 1

Over the vocal cords and decays from here and the biggest velocity is at about the 3rd birfurcatuin

Question 2

What kind of flow is at the voal cords and in airways?

Answer 2

Turbulent over vocal cords and laminar in airways

Question 3

What are the determinants of airway resistance?

Answer 3

Viscosity, length and radius (under laminar conditions)

Question 4

Define laminar flow

Answer 4

occurs when a fluid flows in parallel layers with no disruption between the layers

Question 5

Define turbulent flow

Answer 5

Flow with no organisation

Question 6

Define transitional flow and when does it occur?

Answer 6

When there is a combination of laminar and turbulent flow and this arises at the birfucation points (laminar until the bifurcation points when it becomes turbulent)

Question 7

During forced inspiration what keeps the small airways open?

Answer 7

positive transmural pressure

Question 8

What factors modulate airway resistance and what is the result of these factors?

Answer 8

NEURALLY MEDIATED
Parasympathetic: bronchial constirction and mucous production increases
Sympathetic: B2 action (smooth muscle relaxation, secretion decreases)
Paco2 increase: local airway dilation
P aco2 decrease:local airway constriction

Question 9

What is static compliance and how is it measured?

Answer 9

When there is no flow and there is a fixed volume

what is actually measured is the total compliance

Question 10

what static compliance changes occur in emphysema and pulmonary fibrosis?

Answer 10

emphysema: large compliance at FRC with loss of recoil
Fibrosis: reduced compliance at FRC and too much recoil

Question 11

What is dynamic compliance?

Answer 11

The change in lung volume during cyclic breathing

Question 12

Compliance changes in emphysema

Answer 12

High static compliance, loss of recoil (has to actively breathe out)

Question 13

Compliance changes in asthma

Answer 13

Increase in compliance (large expiratory work)

Question 14

Compliance changes in respiratory distress syndrome

Answer 14

Low static and dynamic compliance

Question 15

Compliance changes in pulmonary fibrosis

Answer 15

will have to work much harder to breathe out but this work will be saved it will be easier to breathe in

Question 16

What is Laplace’s law and how does this explain why it is harder to blow up a small lung

Answer 16

P=2t/r

A higher pressure is needed to maintain stability in smaller alveolus

Question 17

How do alveoli overcome Laplace’s law?

Answer 17

they are interdependent: physically interconnected with each other and lined with surfactant

Question 18

What is the role of surfactants?

Answer 18

To reduce the surface H2O and hence the surface tension: it is an attractive source of surface molecules that tends to minimise surface area

Question 19

what cells produce surfactant?

Answer 19

Alveolar type 2 cells

Question 20

What happens to surfactant during inspiration?

Answer 20

As alveolar surface increases and [surfactant] decreases, surfcatant from micelles recruited to surface

Question 21

What happens to surfactant during expiration?

Answer 21

Alveolar surface decreases, [surfactant] is higher and surfactant then reforms micelles

Question 22

What happens in rapidly expanding alveoli?

Answer 22

[surfactant] decreases - calcium decreases - ventilation decreases

Question 23

What happens in slowly expanding alveoli?

Answer 23

[surfactant] increases - calcium increases - ventilation increases