Week 2 - Mechanics Of Breathing

Question 1

What is compliance?

Answer 1

The sketchiness of the lungs, volume change per unit of pressure, higher compliance means easier to stretch

Question 2

What factors affect compliance?

Answer 2

Supine/prone position, laparoscopic surgical interventions, severe restrictive pathologies, chronic restrictive pathologies, hydrothorax (pleural effusion), pneumothorax, high standing of diaphragm

Question 3

Why might certain things affect compliance?

Answer 3

Reduced AP motion, increased intrabdominal pressure, fibrosis/myasthenia gravis, asbestosis/motor neurone disease, congestive heart failure, physical trauma/diseased lung, obesity/pregnancy

Question 4

What causes elastic recoil of lungs?

Answer 4

Elastic tissue of airways

Surface tension of fluid lining alveoli

Question 5

How is compliance reduced?

Answer 5

By surface tension of lining fluid

Question 6

What is surface tension?

Answer 6

Water molecules attract each other

Interface of air and fluid makes the surface resistant to stretching

Question 7

How does surface tension affect stretchiness of lung?

Answer 7

Makes it harder for the lung to stretch

Force is required to stretch alveoli mainly because its used to stretch the lining fluid

Question 8

How is surface tension in the lungs reduced?

Answer 8

Surfactant disrupts interactions between surface molecules - breaks up hydrogen bonds
This makes it easier to inflate

Question 9

What is surfactant made of?

Answer 9

90% phospholipids

10% protein

Question 10

What is the important protein in surfactant?

Answer 10

Surfactant protein A

Question 11

What cell type produces surfactant?

Answer 11

Type 2 alveolar cells (pneumocyte)

Question 12

Why are little breaths easy but big breaths (forced inspiration) hard?

Answer 12

Surfactant reduces surface tension when lungs are deflated but less so when fully inflated so this makes it harder to stretch the lungs

Question 13

What is Laplace’s law for calculating pressure?

Answer 13

Pressure = (2 x surface tension) / radius

Question 14

How does the lung keep its structure so the big alveoli don’t ‘eat’ the little ones?

Answer 14

As alveoli coated with surfactant get bigger the surface tension in their walls increases so pressure increases proportionally

Question 15

What is surfactants role in maintains pressure in alveoli?

Answer 15

Equalised pressure between different sizes of alveoli so they don’t collapse into each other

Question 16

What is infant respiratory distress syndrome?

Answer 16

Babies born prematurely (less than 36 weeks) have too little surfactant which makes the lungs very stiff and they have few large alveoli
This means breathing and gas exchange is compromised

Question 17

What is resistance like in the lungs?

Answer 17

Have many very small airways so individual resistance is high but the viscosity of air is very low and there are loads in parallel so this compensates for the increased resistance as the air passes down

Question 18

Where does the highest resistance occur in the lungs?

Answer 18

In the trachea and bronchi

Question 19

Where is the lowest resistance in the lungs?

Answer 19

In the small airways

Question 20

What happens when the lung is compressed?

Answer 20

Raised intrathoracic pressure means small airways are narrowed and resistance increases dramatically and air is trapped in alveoli

Question 21

Why is breathing out more difficult in diseases such as asthma and bronchitis?

Answer 21

Inspiration is ok as airways can expand and lower resistance but expiration is a problem as resistance increases much earlier so breathing out can become very difficult