Lecture 4: The dynamics of ventilation

Question 1

What two factors contribute to the recoil of the lung tissue itself during expriation?

Answer 1

• Elasticity of the lung tissue

- Surface tension of the alveoli

Question 2

What is elasticity of the lungs proportional to?

Answer 2

1/compliance

Question 3

What is elasticity defined as?

Answer 3

Ability to recover original size and shape after deformation

Question 4

What creates the elasticity properties of lung tissue // recoil force?

Answer 4

Elastin and collagen of the lungs

Question 5

How is recoil force generated?

Answer 5

Elastic and collagen in the airways, alveoli, vessels

create radial traction during inspiration and this generates the passive recoil force of the tissues.

Question 6

What is the relationship of elasticity and compliance?

Answer 6

Compliance is inversely proportional to elasticity

This means as elasticity decreases, compliance increases. i.e in disease states compliance changes with elasticity

Question 7

What is the equation of compliance?

Answer 7

Change in volume / change in pressure

Question 8

Given the lungs have compliance, what else has compliance? and when are they equal?

Answer 8

The chest wall

At FRC the chest wall and lung compliance are equal

Question 9

On the pressure volume curve what is the flat part of the inspiration curve? (1)

Answer 9

Surface tension of collapsed airways prevent opening till increased pressure

Question 10

Describe the deflation part of the PV curve;

Answer 10

Inflation pressure on deflation is less i.e lung more compliant

Surface tension is a deflation pressure i.e it changes compliance on deflation

Question 11

What is the PV relationship of the lungs known as?

Answer 11

A hysteresis

Question 12

What happens to the lungs when they are filled with fluid, when it comes to PV relationship?

Answer 12

The curve is left shifted, removes the liquid air interface i.e no surface tension

Question 13

What is surface tension?

Answer 13

Cohesive force between neighbouring molecules of a liquid BUT those at the air-gas interface, exhibit stronger forces to their neighbouring molecules as they dont have any molecules where the air is. = surface tension

Question 14

Whats the law of laplace in the lung?

Answer 14

P = 2T/R in the alveoli

i.e if you had two balloons of different size, air would flow from the smaller to the larger one as the pressure would be greater in the smaller balloon….

Question 15

What does the law of laplace predict for alveoli?

Answer 15

In the absence of surfactant the pressure to inflate would be 30cm of water

Question 16

Why is surfactant good when it comes to pleura?

Answer 16

Because plural pressure is -3 -> -6 cm water, so surfactant decreases alveolar inflation pressure

Question 17

Write some notes on pulmonary surfactant:

Answer 17

Composition: Phospholipid
Origin: Type 2 alveolar cells
Function: To reduce surface tension
Release: During inspiration // inhalation (sighing)

Question 18

What does inspiring do to the liquid gas interface?

Answer 18

1) Increases surfactant

2) Decreases surface tension

Question 19

On the hysteresis what prevents further air release?

Answer 19

Airway collapse prevents further air release

Question 20

What happens to PV /compliance in disease states?

Answer 20

Increased compliance i.e COPD (very difficult to defflate)

Decreased compliance i.e Fibrosis (very hard to inflate)