Respiratory Systems 11 - Lung Mechanics

Question 1

Why is the inspiratory curve stunted in variable extrathoracic obstruction?

Answer 1

The obstruction is outside of the thorax, so there is difficulty breathing in (imagine a piece of paper covering the mouth)

Question 2

Why is the expiratory curve stunted in variable intrathoracic obstruction?

Answer 2

• As there is an obstruction in the lung
• Imagine a piece of paper covering the bottom of the trachea, which opens when you breathe in and closes when you breathe out
• The curve is much more affected than the inspiratory curve in extrathoracic obstruction

Question 3

Why are both expiratory and inspiratory curves stunted in fixed airway obstruction?

Answer 3

• As it is almost as though the trachea is crushed, so the air cannot pass through the trachea
• Therefore, it is hard to breathe in and to breathe out.

Question 4

Why do obstructive diseases increase overall volume (shift left) and restrictive diseases decrease overall volume (shift right)?

Answer 4

• Because you cant breathe in much

- Like having a big bear hug

Question 5

List some obstructive lung diseases

Answer 5

Chronic causes

• COPD
• Emphysema
• Bronchitis

Acute causes
- Asthma

Question 6

List some restrictive lung diseases

Answer 6

Pulmonary

• Lung fibrosis
• Interstitial lung disease

Extrapulmonary causes

• Obesity
• Neuromuscular disease

Question 7

Describe what pressure volume curves show

Answer 7

• If they have a higher volume, shorter pressure range and steeper gradient, then there is an obstructive lung disease
• If there is a curve at a lower volume with a larger pressure range and small gradient, this is a restrictive disease

Question 8

Define compliance

Answer 8

The tendency to distort under pressure

volume change/ pressure change

Question 9

Define elastance

Answer 9

The tendency to recoil to the original volume (inverse of compliance)

(pressure change/ volume change)

Question 10

Why are fluid filled lungs more compliant than air filled lungs?

Answer 10

• The air- water interface exhibits surface tension

- The fluid - water interface does not.

Question 11

Describe the role of surfactant, and why it can perform this function

Answer 11

• Surfactant decreases surface tension in the lungs
• This is by filling in the gaps between water molecules to break the surface tension
• Prevents the collapse of small alveoli (law of laplace
• Increases compliance
• Reduces the work of breathing

Question 12

How are resistance and conductance related?

Answer 12

Resistance is inversely proportional to the fourth power of the radius

Question 13

How does resistance change through the airway generations?

Answer 13

• Resistance first increases until around the fifth generation
• The resistance then decreases with a steep gradient as there is a large decrease in radius
• As you get far down the airways, there is no change in resistance

Question 14

How does resistance change as lung volume increases?

Answer 14

• Resistance decreases, at first rapidly and then more slowly.
• This is because the airways are not rigid, they dilate as the lung volume increases

Question 15

How does the conductivity of the airways change with increasing lung volume?

Answer 15

Conductivity increases

Question 16

Why is cartilage so important in the trachea during hard expiration?

Answer 16

• As in hard expiration, the airway transmural pressure can fall to -2
• This would result in the trachea collapsing

Question 17

What cells produce surfactant?

Answer 17

Type 2 pneumocytes

Question 18

Describe the shape of the pressure volume relationship in the lung

Answer 18

Sigmoid