Lung mechanics 2 Flashcards
How do you measure lung compliance?
Work out change in volume (spirometer) and change in pressure
alveolar pressure = 0, intrapleural pressure measured by oesophageal balloon
delta V/delta P
What are the axes for a static pressure volume loop calculating lung compliance?
x axis = pressure
y axis = volume
Which of inspiration and expiration causes the lungs to have a greater volume for the same pressure?
Expiration
When do the lungs have minimum compliance?
High and low volumes
When do the lungs have maximum compliance?
Around normal tidal volume
What is a typical value for lung compliance in an adult male?
1.5L/kPa
What kind of compliance does a stiff lung have?
Low compliance
What kind of compliance does a fibroses lung (e.g. asbestosis) have?
Low compliance
What kind of compliance does the lung of an emphysema patient have?
High compliance (tissue destruction - becomes floppy)
What diseases make up COPD?
Chronic bronchitis
Emphysema
What occurs in bronchiolitis?
Thick, narrow bronchioles with excess mucus
What occurs in emphysema?
Destruction of alveolar walls
What gives the lung elastic resistance?
Elastin and collagen
How can you stretch an air-fluid interface?
Overcome its surface tension
What is the La Place equation? (surface tension)
P = 2T/R (R = radius)
If there is high surface tension on a bubble what does it want to do?
Collapse in (more pressure)
If the bubble has a bigger radius, is it more or less likely to collapse inwards?
Less likely
Pressure decreases when radius increases
What do we need to do to prevent small alveoli in the lung collapsing inwards?
Reduce the surface tension
What does surfactant do?
Reduces the surface tension and increases compliance (stops alveoli collapsing in on themselves)
What is surfactant produced by?
Type II alveolar cells
What is surfactant made up of?
Phospholipids and surfactant proteins
How does surfactant work?
The phospholipids have a hydrophobic and a hydrophilic end
They stop the water molecules getting close together
What kind of alveoli is surfactant at high concentration?
Small alveoli
What is transudation?
Fluid being sucked into alveoli
What causes neonatal respiratory distress syndrome?
Inadequate surfactant production in premature babies
- increased work of breathing (low lung compliance)
What is alveolar dependency?
Alveoli join together (also prevents collapse)
What is restrictive lung disease?
Resistance to stretch of alveoli
What is obstructive lung disease?
Difficulty in air flowing through tubes (airways resistance)
Tubes narrow
Give examples of obstructive lung diseases
asthma
bronchiolitis/ chronic bronchitis
emphysema
COPD
Give examples of restrictive lung diseases
Fibrosis of the lung
Respiratory muscle weakness
Phrenic nerve damage
TB
In which obstructive lung diseases are the alveoli fine?
Asthma and chronic bronchitis
How can you measure lung function in clinic?
Peak flow (forced expiratory flow) Spirometry
What is FEV1?
Forced expiratory volume in 1 second
What is FVC?
Forced vital capacity
What is a normal FEV1/FVC ratio?
Over 75%
What happens to the FEV1/FVC ratio in obstructive disease?
Decreases (FEV1 very very low)
What happens to the FEV1/FVC ratio in restrictive disease?
It is normal (or even higher)
both FEV1 and FVC decrease
What is the hallmark of restrictive lung disease?
Low vital capacity
What does a maximum flow-volume loop look like in COPD patient?
Concave inwards
What does a maximum flow-volume loop look like in restrictive lung disease patient?
No concave section
Just small loop, otherwise normal
How does asthma effect compliance?
No effect
What happens to the FRC in a fibrosed lung?
Reduced because increased lung recoil
What happens to the FRC in the lung of an emphysema patient?
Increased because decreased lung recoil
–> barrel chest
