Exam #3: Respiratory Mechanics

Question 1

What anatomical events occur during expiration?

Answer 1

Diaphragm relax

Question 2

What anatomical events occur during inspiration

Answer 2

Diaphragm contraction

Question 3

What is the function of the rib cage?

Answer 3

Sustain negative pressure around the lung

Question 4

What are the muscles of inspiration?

Answer 4

Diaphragm
External intercostals
Scaleni
SCM

Question 5

What happens in diaphragmatic paralysis?

Answer 5

• Conditions established for development of pneumonia

- External intercostals, SCM, & scalini muscles become active in quiet inspiration to compensate

Question 6

What happens in sub-diaphragmatic abscess

Answer 6

• Conditions established for development of pneumonia

- External intercostals, SCM, & scalini muscles become active in quiet inspiration to compensate

Question 7

What is the effect of intercostal muscle paralysis?

Answer 7

Little

Question 8

What does visible contraction of the scaleni muscles indicate?

Answer 8

Dyspnea

Question 9

What are the muscles of expiration?

Answer 9

Abdominal wall muscles

Question 10

What happens in congenital absence of abdominal wall muscles?

Answer 10

Fatal

Question 11

What is the intrapleural pressure?

Answer 11

Negative

Suction activity

Question 12

What is the transmural pressure?

Answer 12

Pressure between alveoli pressure & pleural pressure

*This is the driving force of respiration

Question 13

How does negative intrapleural pressure lead to alveolar ventilation?

Answer 13

Pressure at the pleural surface is transmitted through the alveolar walls

Question 14

What can cause a positive intrapleural pressure?

Answer 14

Pneumothroax

Question 15

What happens to lung pressure during inspiration?

Answer 15

Negative alveolar pressure brings air in

Question 16

When is the transpulmonary pressure largest?

Answer 16

End of inspiration

Question 17

How does the pleural pressure change with inspiration?

Answer 17

Decrease

Question 18

Outline the breathing sequence.

Answer 18

1) Brain initiates
2) Phrenic nerve
3) Diaphragm contracts (drops)
4) Throacic volume increases
5) Intrapleural pressure becomes more negative
6) Alveolar transmural pressure gradient increases
7) Aleveoli expand

Question 19

What is the difference between passive & active expiration?

Answer 19

• Expiration is a passive process normally

- Expiration is active is pathological states

Question 20

What is Hooke’s law? How does it relate to pressure & volume?

Answer 20

For an elastic structure, the increase in length varies directly with the increase in force until the elastic limit is reached

Question 21

What is compliance in relation to Hooke’s law?

Answer 21

Compliance is the slope of the pulmonary pressure volume curve.

Steeper slope= more compliance
Shallower slope= less compliance

Question 22

Draw the pressure volume curve for inspiration & expiration. Why are the curves different?

Answer 22

During inspiration you have to overcome the partially collapsed phase of the alveoli

Question 23

How is compliance measured clinically?

Answer 23

Expiration limb of the pressure volume curve

Question 24

What are the determinants of lung compliance?

Answer 24

Elastin

Collagen

Question 25

Write the law of Laplace.

Answer 25

N/A

Question 26

How does alveolar radius relate to pressure?

Answer 26

Decreased radius increases the pressure tending to collapse an alveolus

Question 27

What is the function of surfactant?

Answer 27

Reduce alveolar surface tension & decrease collapsing force

Question 28

What cell type secretes surfactant?

Answer 28

Type II pneumocytes

Question 29

What is the main component of surfactant?

Answer 29

Lecithin

Question 30

How does Lecithin concentration vary with gestation?

Answer 30

Lecithin increases at 33 weeks

Question 31

What is the clinical significance of the sphingomyelin/ lecithin ratio?

Answer 31

Decrease in ratio means that surfactant production is NOT sufficient

–> Infantile Respiratory Distress Syndrome

Question 32

What is the relationship between lung compliance & chest wall compliance?

Answer 32

Lungs tend to collapse

Chest tends to spring out

Question 33

Draw the chest wall- lung combined compliance curve.

Answer 33

N/A

Question 34

How does increased lung compliance alter the pressure-volume curve?

Answer 34

Increased lung compliance

• Loss of elastic fibers
• Compliance increases
• Higher FRC
• Breathes at higher lung volumes
• Barrel-shaped chest

Question 35

How do changes in decreased chest wall compliance alter lung compliance?

Answer 35

asdf

Question 36

How does a decrease in lung compliance alter the pressure-volume curve. Aside from fibrosis, when is this commonly seen?

Answer 36

Seen in pneumonia, pulmonary edema, & lung fibrosis

• Decreased slope of pressure volume curve
• Lower FCR

Question 37

What determines pulmonary resistance? Write pisouille’s law.

Answer 37

N/A

Question 38

Where are the greatest changes in resistance seen?

Answer 38

Broncioles

Question 39

What clinical conditions can increase resistance?

Answer 39

Asthma

Bronchitis

Question 40

What happens to resistance with PNS stimulation?

Answer 40

M3 activation

Asthma
Muscarinic agents

Increase resistance

Question 41

What happens to resistance with SNS stimulation?

Answer 41

B2 activation

Epinephrine
Albuterol

Decreased resistance

Question 42

What happens to pulmonary resistance in exercise?

Answer 42

Traction increases, leading to a decrease in resistance