2.18 - Mechanical Properties Of Lung & Chest Wall

Question 1

Where is flow in the respiratory system greatest?

Answer 1

Over the vocal cords

Question 2

Why does flow decrease as it passes through the respiratory system?

Answer 2

Because cross sectional area increases

Question 3

Where in the respiratory system does turbulence arise?

Answer 3

At points of bifurcation. As flow in rest of lung is laminar, flow in the lung as a whole is described at transitional

Question 4

What components of the airways contribute the most to airway resistance?

Answer 4

Pharynx - Larynx: 0.6 Upper airways (>2mm): 0.6 Lower airways (<2mm): 0.3 (greatly increase in COPD) Total resistance: 1.5

Question 5

What are the three determinants of airway resistance?

Answer 5

viscosity (air, so relatively constant), length and resistance

Question 6

How can airway resistance be modulated?

Answer 6

Via actions on smooth muscle tone: Parasympathetic: bronchial constriction and increased mucous production. Sympathetic: beta2 action leads to smooth muscle relaxation and decreased secretions

Also changes in gas partial pressures. Increased Paco2 leads to local airway dilation.

Question 7

Describe the association between lung compliance and chest wall compliance

Answer 7

At tidal volume, chest wall compliance is approxiamtely the same as lung compliance.

Question 8

Describe the change in lung compliance in fibrosis and emphysema

Answer 8

Emphysema has large compliance due to the loss of elastic recoil

Fibrosis had greatly reduced compliance due to too much recoil

Question 9

Describe the use of surfactants in the lung

Answer 9

Surfactants are produced by the Alveolar Type 2 Pneumocytes to reduce the surface tension caused by water.

Question 10

Describe the changes in surfactant levels during respiration

Answer 10

Surfactant can form micelles

During inspiration, as alveolar surface increases and [surfactant] decreases, surfactant from micelles is recruited to surface

During expiration, alveolar surface decreases, [surfactant] is high and surfactant then reforms micelles

Question 11

What is the best estimate of her static lung compliance?

Anna May, a 43 year old female, has an extensive lung function analysis. As she exhales under static conditions from FRC + 1L to FRC, her oesophageal pressure changes from -10 to -5cm H2O and the alveolar pressure from 5 to 0cm H2O.

A: 0.5L/cm H2O

B: 5.0cm H2O/L

C: 0.1L/cm H2O

D: 2.0cm H2O/L

E: 0.2L/cm H2O

Answer 11

C