SFP: airway resistance and compliance

Question 1

What is the biggest factor in resistance to airflow?

Answer 1

The diameter of the airways

Question 2

What factors impact airway resistance?

Answer 2

Viscosity, length of the airway, and caliber (radius)

Question 3

In the first 3 branching’s of the airway system, what happens to cross-sectional area? How does this impact resistance?

Answer 3

It decreases, causing resistance to temporarily go up

Question 4

Describe resistance at high and low lung volumes.

Answer 4

At high volumes, resistance is lower, making it easier for air to flow. At low volumes, resistance is higher, meaning airways can collapse.

Question 5

What is conductance?

Answer 5

The reciprocal of resistance; it increases as lung volumes increase.

Question 6

Describe local control of airway caliber.

Answer 6

Hypo and hyperventilation can impact local PCO2 and change airway caliber. Local hypoventilation raises local PCO2, causing bronchodilation. Local hyperventilation lowers local PCO2, causing bronchoconstriction.

Question 7

Describe autonomic control of airway caliber.

Answer 7

Parasympathetic system causes bronchoconstriction, and sympathetic causes bronchodilation.

Question 8

Describe inflammatory control of airway caliber.

Answer 8

Chemicals associated with inflammation such as histamine, thromboxane A2, PGF2, and leukotrienes lead to bronchoconstriction. This is seen in asthma.

Question 9

Describe how forced expiration impacts caliber.

Answer 9

Forced expiration can cause pleural pressure to become positive and greater than the pressure inside the airway, leading to compression of airways. This reduces the caliber which limits flow of air.

Question 10

What is equal pressure point?

Answer 10

The point at which the pressure inside the airway equals the pressure that surrounds the airway.

Question 11

Relate equal pressure point, caliber, and forced exhalation.

Answer 11

During forced expiration, airways past the equal pressure point (more toward the mouth) become compressed due to the pressure outside being greater than the pressure inside the airway. This causes a negative trans airway pressure and airway collapse beyond the equal pressure point, causing airflow to be effort independent and limited.

Question 12

What is true of the equal pressure point in the absence of lung disease?

Answer 12

It is in airways that contain cartilage, so collapse is resisted.

Question 13

What causes the equal pressure point to move closer to alveoli?

Answer 13

Decreased lung volume, airflow obstruction, and decreased elastic recoil pressure.

Question 14

What is normal FEV1/FVC ratio?

Answer 14

0.7

Question 15

What is transitional airflow?

Answer 15

Air encounters bifurcations, disrupting laminar flow and establishing eddies.

Question 16

Where is airflow truly turbulent?

Answer 16

Trachea

Question 17

Where is airflow transitional?

Answer 17

Throughout most of the tracheobronchial tree.

Question 18

What determines compliance in the lung?

Answer 18

Properties of the tissue that allow deformation and reformation, and surface tension of the alveolar walls.

Question 19

What happens to compliance of the lungs as we age?

Answer 19

It increases due to decreasing elasticity.

Question 20

The higher the compliance, the ___ it is to expand the lungs.

Answer 20

Easier

Question 21

When is compliance of the lung greatest? Lowest?

Answer 21

It is greatest as the residual volume is approached, and is lowest at high lung volumes.

Question 22

What does decreased compliance do to FEV1 and the FEV1/FVC ratio?

Answer 22

It will decrease FEV1, but the ratio is maintained.

Question 23

What does increased compliance do to FEV1 and the FEV1/FVC ratio?

Answer 23

Increased compliance means lowered elastance, which means it will be more difficult to move air out. This as a result lowers both FEV1 and the FEV1/FVC ratio.

Question 24

Describe surface tension.

Answer 24

Forces between molecules lining the alveoli are stronger than forces between the molecules and alveolar gas, causing the film on the alveoli to shrink to its smallest surface area.

Question 25

What helps reduce surface tension on alveoli?

Answer 25

Surfactant

Question 26

What are the 4 big purposes of lung surfactant?

Answer 26

1. Reduced surface tension 2. Increased lung compliance and reduced work of breathing 3. Reduces tendency of alveolar collapse 4. Keeps lung tissue ‘dry’.

Question 27

Describe infant respiratory distress syndrome.

Answer 27

Collapsed and poorly expanded alveoli are less compliant than the chest wall due to insufficient surfactant. Increased inspiratory effort creates negative intrapleural pressure and non-improved tidal volume.

Question 28

How can we treat IDS?

Answer 28

ECMO, exogenous surfactant, corticosteroids.

Question 29

Describe how a lack of surfactant impacts compliance.

Answer 29

It directly lowers it.

Question 30

What is functional residual capacity?

Answer 30

The volume of air remaining in the lungs after normal tidal expiration; it is the volume at which the tendency of the lung to recoil inward and the chest wall to recoil outward are balanced.

Question 31

Describe FRC in emphysema.

Answer 31

Increased lung compliance increases FRC due to a lowered tendency of the lung to recoil from lowered elastance.

Question 32

Describe FRC in kyphoscoliosis.

Answer 32

Compliance of the chest wall decreases, decreasing FRC due to a lower volume of air entering at the same pressures.

Question 33

What does a more negative intrapleural pressure do to alveoli?

Answer 33

Makes them bigger due to an extending force. This is seen at the apices of the lungs.

Question 34

Which parts of the lung have higher ventilation? Why?

Answer 34

Lower lobes due to increased compliance from gravity. The apices of the lungs have lower ventilation.

Question 35

Restrictive lung diseases need to overcome…

Answer 35

Elastic component

Question 36

Obstructive lung diseases need to overcome…

Answer 36

Resistance component (low compliance)