Lung Mechanics-Scharf

Question 1

How does the physiology (PV curve) of the lung change at higher vs lower lung volumes?

Answer 1

Lung is stiffer (less compliant) at higher lung volumes.

Question 2

What is the result of a loss of collagen and elastin in the lung?

Answer 2

Destruction of alveolar structure, floppy, higher compliance in alveoli. Causes hyperinflation. For same pressure, large increase in volume. Ex: emphysema.

Question 3

What is the most important factor in elasticity of the lung?

Answer 3

Surface tension. Proportional to tension and radius.

Question 4

LaPlace’s law in bubbles

Answer 4

T=Δ Pr/m, m=membrane thickness

Question 5

What is hysteresis?

Answer 5

Lung remains inflated at a lower pressure during deflation than during inflation. Explained by surface tension.

Question 6

What’s the difference between saline inflation and air inflation?

Answer 6

1. Easier inflation with saline. (Higher compliance, less elastic recoil.) 2. No hysteresis.

Question 7

What is the active ingredient in surfactant?

Answer 7

Phospholipid: dipalmityl lecithin

Question 8

What creates surfactant?

Answer 8

Lamellar bodies in type 2 alveolar pneumocytes in epithelium

Question 9

What are the roles of surfactant?

Answer 9

1. Decreases surface tension (decreases transpulmonary pressure needed to inflate the lung) 2. Improves the stability of air sacs (As alveoli are smaller so is the surface tension) 3. Helps keep alveoli dry: with large surface tension, the retractile forces in alveoli would tend to pull water in from capillaries to alveoli. 4. Responsible for pressure – volume hysteresis of the lung 5. Some surfactants are also immune modulators 6. Appears in neonatal lungs late in gestation

Question 10

What is the effect of pulmonary fibrosis on the PV curve?

Answer 10

Flatter, more stiff.

Question 11

What is the ventilatory pressure at resting state?

Answer 11

Airway (inward) -atomspheric pressure (0 outwards)

Question 12

What are the components of the pressure acting on the lung?

Answer 12

Airway pressure (inward) - Pleural pressure (outward)

Question 13

What are the components of the chest wall pressure?

Answer 13

Pleural pressure (outward) - atmospheric pressure (0)

Question 14

Graph of interaction of lung and chest wall pressure vs vital capacity and TLC with FRC intersect.

Answer 14

Question 15

What causes reduced FRC?

Answer 15

Obesity (by stiffening chest wall), fibrosis (by stiffening lungs).