Lung Mechanics

Question 1

What is the work of breathing deterimined by

Answer 1

lungs

Thoracic compliance

Airway resistance

Question 2

What is compliance

Answer 2

Ease with which lungs can be expanded

Question 3

What is embedded in elastic tissue

Answer 3

Lungs

Airway tree

Vascular tree

Question 4

What is trans-pulmonary pressure

Answer 4

P difference between alveoli and pulmonary wall

Question 5

If lungs are easy to inflate, what sort of compliance do they have

Answer 5

Increased compliance

Question 6

Formula for compliance

Answer 6

Change in vol/change in P

Question 7

Transpulmonary pressure difference from apex to base

Answer 7

APEX = -10

MIDDLE = -5

BASE = -2.5

-ve P is the suction that keeps the lungs open

Question 8

1. Where is there greater alveolar volume
2. Where is there greater alveolar ventilation

Answer 8

1. Apex
2. Base

Question 9

Which part of the lung is most compliant

Answer 9

Base of lung

Smaller alveoli at base => easier to expand alveoli at base

Question 10

What does lung compliance depend on

Answer 10

1. Distensibility - easy to stretch/deflate - ELASTIN
2. Elasticity - w/o it, lungs would enlarge with every breath and compliance would be 0 - COLLAGEN
3. Surface tension

Question 11

Consequence of decreased compliance

Answer 11

Increased stiffness, increased work to inflate lungs

Question 12

Background of pneumonia

Answer 12

Fluid in lung tissue, alters surface tension of alveoli, changes surfactant and makes it more difficult to control lungs

Question 13

conditions affected by compliance

Answer 13

Fibrosis

COPD

Emphysema

Chronic bronchitis

Question 14

Factors that influence compliance

Answer 14

• Posture
• Age
• Post-laproscopic surgery
• Occasional deep breaths
• Pregnancy
• High standing diaphragm - obesity, scoliosis
• Lung disease
• Pneumothorax - trauma, diving, underlying lung pathologies

DECREASED COMPLIANCE WHEN:

Lung is unventilated for long period, increased surface tension within alveoli, lungs engorged with blood (increase pulmonary venous pressure)

Question 15

High or low compliance with EMPHYSEMA

Answer 15

HIGH C_L

Question 16

High or low compliance with FIBROSIS

Answer 16

Low C_L

Question 17

2 determinants of lung compliance

Answer 17

R due to elasticity of lung (25%)

• Elastic fibres in interstitium of alveolar walls
• Thick alveolar wall => increased elastic fibres => increased R to stretch

Surface tension @ air-water interface in alveoli (75%)

• Alveolar spaces lined with a thin layer of water
• Attractive forces between water molecules (= ST) counteracts expansion of water lining
• Energy is required to overcome ST of this water layer in order to expand

Question 18

When is surfactant produced and how

What is its composition

Answer 18

Produced by type II alveolar cells from week 28 gestation

90% lipids, 10% proteins => AMPHIPHATIC

Question 19

Infant respiratory distress syndrome

Answer 19

Decreased C_L

Atelectasis

Oedema

Exogenous surfactant

Question 20

#AD

Name the 2 large hydrophilic surfactant proteins

Answer 20

1. SP A
2. SP D

Question 21

Name the 2 small hydrophobic surfactant proteins

Answer 21

1. SP B
2. SP C

Question 22

Name the 7 lipids in surfactant

Answer 22

1. Dipalmitoylphosphatidylcholine (DPPC - 60%)
2. Phosphatidylglycerol
3. Phosphatidic acid
4. Phosphatidylinositol
5. Phosphatidylethanolamine
6. Phosphatidylcholine
7. Cholesterol - most abundant neutral lipid present

Question 23

1. How much surface tension does DPPC produce
2. What does it form

Answer 23

1. Generates near 0 surface tension at interface during compression
2. Forms tightly packed monolayer which can generate these low ST values w/o collapsing

intermolecular repulsive forces oppose attractive forces between liquid surface H2O molecules

EFFECT IS STRONGER AT LOWER ALVEOLAR VOLUMES

Question 24

Deficiency of SP A

Answer 24

More susceptible to pathogens

Question 25

SP B

Answer 25

Decreases surface tension SP B deficiency in humans leads to RDS (resp distress syndrome) Stabilises lipid monolayers anti-bacterial

Question 26

SP C

Answer 26

found only in lungs Linked to SP B

Question 27

Physiological roles of surfactant proteins

Answer 27

1. Decrease ST to increase compliance - decreased work of expanding lungs at each breath 2. Increased stability of alveoli - decrease small alveoli emptying into larger ones 3. Helps to keep alveoli dry because ST of alveolus liquid layer would draw water into alveolus

Question 28

Law of Laplace

Answer 28

P = 2T/r P is greater in smaller alveolus

Question 29

Hysteresis

Answer 29

V/P relationship is different during expiration

Question 30

What is vol at any pressure greater for

Answer 30

Greater for deflation than inflation

Question 31

What does most of hysteresis and C_L appear due to

Answer 31

Surface tension of alveoli

Question 32

How does surface tension affect alveoli

Answer 32

Inflation of lungs with saline eliminates air-liquid interface and surface tension Musch easier to inflate lungs with saline - elastic recoil is diminished due to lack of ST - not much difference between inflation and deflation =\> no HYSTERESIS

Question 33

3 reasons for hysteresis

Answer 33

1. **_Changes in surfactant activity_** - ST greater in inspiration 2. **_Stress relaxation_** - inherent property of elastic tissue - crinkled structure of collagen in lungs 3. **_Re-distribution of gas_** - fast and slow alveoli

Question 34

Relationship between lung and chest wall

Answer 34

Lung and chest wall in series with each other - total compliance

Question 35

1. Lung compliance 2. Chest wall compliance 3. Total compliance

Answer 35

1. Change in lung vol/change in P_tp 2. Change in lung vol/change in trans-chest wall P 3. 100 ml/cmH₂O