Exam #3: Respiratory Mechanics Flashcards
What anatomical events occur during expiration?
Diaphragm relax
What anatomical events occur during inspiration
Diaphragm contraction
What is the function of the rib cage?
Sustain negative pressure around the lung
What are the muscles of inspiration?
Diaphragm
External intercostals
Scaleni
SCM
What happens in diaphragmatic paralysis?
- Conditions established for development of pneumonia
- External intercostals, SCM, & scalini muscles become active in quiet inspiration to compensate
What happens in sub-diaphragmatic abscess
- Conditions established for development of pneumonia
- External intercostals, SCM, & scalini muscles become active in quiet inspiration to compensate
What is the effect of intercostal muscle paralysis?
Little
What does visible contraction of the scaleni muscles indicate?
Dyspnea
What are the muscles of expiration?
Abdominal wall muscles
What happens in congenital absence of abdominal wall muscles?
Fatal
What is the intrapleural pressure?
Negative
Suction activity
What is the transmural pressure?
Pressure between alveoli pressure & pleural pressure
*This is the driving force of respiration
How does negative intrapleural pressure lead to alveolar ventilation?
Pressure at the pleural surface is transmitted through the alveolar walls
What can cause a positive intrapleural pressure?
Pneumothroax
What happens to lung pressure during inspiration?
Negative alveolar pressure brings air in
When is the transpulmonary pressure largest?
End of inspiration
How does the pleural pressure change with inspiration?
Decrease
Outline the breathing sequence.
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
What is the difference between passive & active expiration?
- Expiration is a passive process normally
- Expiration is active is pathological states
What is Hooke’s law? How does it relate to pressure & volume?
For an elastic structure, the increase in length varies directly with the increase in force until the elastic limit is reached
What is compliance in relation to Hooke’s law?
Compliance is the slope of the pulmonary pressure volume curve.
Steeper slope= more compliance
Shallower slope= less compliance
Draw the pressure volume curve for inspiration & expiration. Why are the curves different?
During inspiration you have to overcome the partially collapsed phase of the alveoli
How is compliance measured clinically?
Expiration limb of the pressure volume curve
What are the determinants of lung compliance?
Elastin
Collagen
Write the law of Laplace.
N/A
How does alveolar radius relate to pressure?
Decreased radius increases the pressure tending to collapse an alveolus
What is the function of surfactant?
Reduce alveolar surface tension & decrease collapsing force
What cell type secretes surfactant?
Type II pneumocytes
What is the main component of surfactant?
Lecithin
How does Lecithin concentration vary with gestation?
Lecithin increases at 33 weeks
What is the clinical significance of the sphingomyelin/ lecithin ratio?
Decrease in ratio means that surfactant production is NOT sufficient
–> Infantile Respiratory Distress Syndrome
What is the relationship between lung compliance & chest wall compliance?
Lungs tend to collapse
Chest tends to spring out
Draw the chest wall- lung combined compliance curve.
N/A
How does increased lung compliance alter the pressure-volume curve?
Increased lung compliance
- Loss of elastic fibers
- Compliance increases
- Higher FRC
- Breathes at higher lung volumes
- Barrel-shaped chest
How do changes in decreased chest wall compliance alter lung compliance?
asdf
How does a decrease in lung compliance alter the pressure-volume curve. Aside from fibrosis, when is this commonly seen?
Seen in pneumonia, pulmonary edema, & lung fibrosis
- Decreased slope of pressure volume curve
- Lower FCR
What determines pulmonary resistance? Write pisouille’s law.
N/A
Where are the greatest changes in resistance seen?
Broncioles
What clinical conditions can increase resistance?
Asthma
Bronchitis
What happens to resistance with PNS stimulation?
M3 activation
Asthma
Muscarinic agents
Increase resistance
What happens to resistance with SNS stimulation?
B2 activation
Epinephrine
Albuterol
Decreased resistance
What happens to pulmonary resistance in exercise?
Traction increases, leading to a decrease in resistance
