Pathophysiology of Respiratory Mechanics

Question 1

3. Summarize the factors affecting the respiratory system elastic recoil and how they -singly or in combination- can affect lung mechanics. (4 factors that effect the compliance)

Answer 1

increased lung compliance (emphysema)
decreased lung compliance (lung fibrosis)
decreased chest wall compliance
normal chest and lung compliance (NM disease)

Question 2

4. Summarize the factors affecting airway resistance and how it is distributed along the tracheobroncial tree. (5)

Answer 2

1. resistance to laminar flow proportional to the length and inversely proportional to the 4th power of the radius
2. lung volume due to traction/ tethering of airways
3. bronchial smooth muscle tone
4. inspired gas properties
5. flow patterns (turbulent v. laminar flow)

Question 3

5. Explain the pathophysiology of airflow obstruction (airway narrowing, dynamic compression etc. )

Answer 3

airway narrowing can cause airway obstruction in asthma or COPD and airway resistance is increased

dynamic compression of intrathoracic airways occurs during forced expiration where the pressure of the the pressure in airways downstream of alveoli is less than alveolar pressure and flow is determined by the difference between alveolar pressure and the pressure outside the airways

Question 4

6. List 4 common chronic lung diseases with airflow obstruction.

Answer 4

1. asthma: due to bronchospasms and mucous production (reversible)
2. chronic bronchitis: due to smoking causing mucous production
3. bronchiectasis: due to airway wall thickening and mucous production
4. emphysema: decreased alveolar and airway tethering

Question 5

1. To produce gas flow in the respiratory system, the respiratory muscle must generate pressures to overcome several impeding forces, describe those two forces.

Answer 5

elastic recoil of the lung and chest wall which opposes stretching or inflation

the resistance to air flow through extrathracic and intra thoracic airways

Question 6

1. Describe the opposition of forces that exist in the chest during rest. (at end of normal unforced expiration)

Answer 6

the lung elastic recoil causes lung collapse while these forces are balanced by the elastic tissues of the chest wall, these are linked by the pleura

this equilibrium is described in volume by the functional residual capacity

Question 7

What does tidal breathing require very little work when FRC and reparatory compliance is nomad?

Answer 7

the inspiratory muscles set the system in motion and potential energy is recovered front eh tendency of the chest wall to expand from tis position at FRC (as FRC increases with aging or disease the work of tidal breathing increases)

Question 8

2. Describe the changes in the volume-pressure relationship in emphysema and pulmonary fibrosis, with special attention to compliance and elastic recoil.

Answer 8

emphysematous lungs are larger and more compliant with less elastic recoil

fibrotic lungs are smaller and less compliant with greater elastic recoil

Question 9

2. Describe the changes in the volume-pressure relationship in emphysema and pulmonary fibrosis, with special attention to compliance and elastic recoil.

Answer 9

emphysematous lungs are larger and more compliant with less elastic recoil

fibrotic lungs are smaller and less compliant with greater elastic recoil

Question 10

3. Describe the forces that are at work at total lung capacity (TLC)

Answer 10

(greatest lung volume achieved by max. voluntary inspiration) occurs at the balance between inspiratory muscle forces and elastic recoil forces (contributed mostly by the lung)

Question 11

How are elastance and compliance related?

Answer 11

compliance is the inverse of elastance

elastance is the sum of forces trying to collapse the lung, whereas compliance is the change in volume per change in pressure

Question 12

When TLC is increased it is usually because _____ is increased. When TLC is low it can be because _____ is low, or it can be due to another reason.

Answer 12

compliance increase is usually the cause of TLC increase and is often the low when TLC is low

Question 13

How would increased or decreased compliance effect the relative position of the volume pressure curve?

Answer 13

floppy, high compliance = left shift

stiff, low compliance= right shift

Question 14

Describe the balance of forces at RV, residual volume.

Answer 14

RV is the lowest lung volume achieved by max. voluntary expiration, it is established by a static balance between expiratory muscle forces and elastic recoiled produced mostly by the chest wall

Question 15

Describe the balance of forces at RV, residual volume.

Answer 15

RV is the lowest lung volume achieved by max. voluntary expiration, it is established by a static balance between expiratory muscle forces and elastic recoiled produced mostly by the chest wall

Question 16

3. Describe 3 conditions that can cause increased total lung capacity and their mechanisms.

Answer 16

1. emphysema via decreased lung elastic recoil
2. acute asthma via (?) decreased chest recoil, decreased lung recoil
3. acromegaly via increased size of lung parenchyma

Question 17

6. Reduced total lung capacity is the hallmark of: ?

Answer 17

restrictive lung disease

Question 18

Respiratory muscle disease don’t change the ____ properties of lung or chest wall.

Answer 18

elastic

Question 19

Respiratory muscle disease don’t change the ____ properties of lung or chest wall.

Answer 19

elastic

Question 20

How does resistance vary with lung volume?

Answer 20

at higher lung volumes, there is greater tethering effect of lung parenchyma, causing an increase in cross sectional area of airways; during expiration, airway resistance increases

positive pleural pressure during forced expiration compresses intrathoracic airways

Question 21

How does resistance vary with lung volume?

Answer 21

at higher lung volumes, there is greater tethering effect of lung parenchyma, causing an increase in cross sectional area of airways; during expiration, airway resistance increases

Question 22

Discuss 3 mechanisms of airway obstruction.

Answer 22

mucous
airway wall thickening
decreased tethering (emphysema)

Question 23

How does decreased elastic recoil contribute to dynamic compression?

Answer 23

less tethering to keep airways open and reduce recoil leads to decreased alveolar pressure

Question 24

Obstructive disorders can have problems with both decreased _____ and increased _____. Restrictive disorders usually have problems with _______ , never have problems with _____.

Answer 24

elastance

resistance