II: Static Properties of Lung & Chest Wall

Question 1

Why is the overall density of the lungs only 0.4 g/cm^3?

Answer 1

This is because the lung is a mixture of blood, water, and air, and air has a very low density.

Question 2

The maximal amount of air we can inhale and exhale depends upon which two factors?

Answer 2

• strength of inspiratory and expiratory muscles

- compliance of pulmonary structures (lung and chest wall)

Question 3

Can we inspire or expire so much air that our lungs pop or collapse, respectively?

Answer 3

No! However, it is possible to destroy the lungs by applying too much positive pressure on the airways using a ventilator or placing a strong suction on the airways with a vacuum cleaner.

Question 4

What are the 4 primary lung volumes?

Answer 4

• Tidal Volume (normal, quiet breathing)
• IRV (extra volume of air available above normal tidal volume)
• ERV (extra volume of air available below normal tidal volume)
• Reserve Volume (air in the lung that is not accessible)

Question 5

What are the 4 secondary lung capacities (defined by mixing and matching 2+ long volumes)?

Answer 5

• Functional Residual Capacity (ERV+RV)
• Inspiratory Capacity (Vt+IRV)
• Vital Capacity (ERV+Vt+IRV)
• Total Lung Capacity (Vt+IRV+ERV+RV)

Question 6

What does the FRC represent?

Answer 6

the balance position of the lung-chest wall system when all respiratory muscles are at rest, or the volume of air present in the lungs at the end of passive respiration

Question 7

What does the inspiratory capacity represent?

Answer 7

the strength of the inspiratory muscles working to stretch out the lungs and chest wall

Question 8

What does the vital capacity represent?

Answer 8

the maximal dynamic range over which the lungs can operate

Question 9

What happens to lung volumes during exercise?

Answer 9

tidal volume goes up at the expense of IRV; FRC is unchanged

Question 10

What are the two ways to inflate lungs?

Answer 10

• apply a negative pressure outside the lung (normal physiological situation)
• apply a positive pressure inside the lung (use of mechanical ventilator)

Question 11

What is the formula for lung compliance?

Answer 11

change in vital capacity over change in translung pressure

Question 12

What happens to lung compliance in pulmonary fibrosis vs. emphysema?

Answer 12

In pulmonary fibrosis, the lungs get stiffer and lose their compliance (shallower slope on compliance graph); in emphysema, the lungs lose their elastic structure and become more compliant (steeper slope on compliance graph).

Question 13

What are 3 major contributors to lung compliance?

Answer 13

collagen, elastin, and surface tension

Question 14

Why can’t the lung and chest wall separate from one another unless air is introduced into intrapleural space (pneumothorax)?

Answer 14

this is due to the serous fluid in between them, which is incompressible/unexpandable

Question 15

Why is it impossible to drive intrapleural pressure down to to 0 L for a closed lung-chest wall system?

Answer 15

The expiratory muscles are not strong enough to further compress the chest wall and rib cage inward.

Question 16

Describe elastin and collagen in terms of elastance vs. compliance.

Answer 16

• collagen: high elastance, low compliance

- elastin: low elastance, high compliance

Question 17

Which forces do muscles of inspiration need to overcome during inflation?

Answer 17

• viscoelastic structures of the lung

- compressive surface tension forces along alveolar epithelium

Question 18

Pulmonary surfactant is secreted by _______.

Answer 18

alveolar type II cells

Question 19

When is pulmonary surfactant in humans typically produced?

Answer 19

in the 28th week of gestation

Question 20

What causes infant respiratory distress syndrome?

Answer 20

insufficient surfactant in babies born prematurely; this can cause breathing to become so labored that their respiratory muscles can fatigue to the point of death

Question 21

Why do alveoli in the lung NOT violate the law of Laplace?

Answer 21

Tension and radius track together, thereby keeping the internal pressures of different sized alveoli identical. This is because small alveoli have a large concentration of surfactant and therefore small surface tension. Large alveoli have a small concentration of surfactant and therefore large surface tension. Thus, P=2(T/r) remains the same.