Week 2 - Lung mechanics Flashcards Preview

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Flashcards in Week 2 - Lung mechanics Deck (23)
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1
Q

What is a pneumothorax?

A

-Break in pleural seal causing air to rush into pleural space due to negative pressure

2
Q

Upon inspiration, what happens to the intrathoracic pressure?

A

-Decreases lower than atm. pressure as volume of lungs increases

3
Q

During expiration what happens to the intrathoracic pressure?

A

-increase due to decreased lung volume

4
Q

What happens to the pressure within the pleural space during inspiration and expiration?

A

-Nothing it always remains negative to outside

5
Q

Why do the abdominal muscles help in forced expiration?

A

-Press on intestines and liver to push diaphragm up to expel more air

6
Q

What is lung compliance?

A

-How stretchy the lungs are (ie how easy the lungs are to inflate)

7
Q

What happens to compliance in emphysema and why?

A

-compliance is increased as elastic fibres are lost in the lung thus recoil is decreased and the lungs are easier to inflate

8
Q

What happens to compliance in fibrosis and why?

A

-Decreases due to stiff lungs becuase of scarring and fibrosis so lungs cannot expand

9
Q

What causes elastic recoil of lungs?

A

-Elastic tissue of airways and surface tension of fluid lining alveoli

10
Q

What is surface tension?

A

-The attraction between water molecules at the interface of fluid and air

11
Q

What reduces surface tension in alveoli? how?

A
  • Surfactant

- Disrupts interactions between surface molecules

12
Q

Why does the effect of surfactant decrease when the lungs are fully inflated? What effect does this have on breathing?

A
  • Limited number of surfactant molecules which are spread more thinly as SA increases
  • Little breaths are easy
  • Big breaths are hard (forced inspiration)
13
Q

What is laplace’s law?

A

-Pressure = (2xsurface tension)/radius

14
Q

What happens to the pressure inside alveoli when alveoli increase in size?

A

-Decreases

15
Q

What happens to the pressure inside alveoli when they decrease in size?

A

-Increases

16
Q

What would happen if there were large alveoli with a lower pressure than small alveoli?

A

-The small alveoli would collapse into the large alveoli (air moves to an area of lower pressure)

17
Q

How does surfactant prevent smaller alveoli collapsing?

A
  • Small alveoli have a high pressure inside them and high amounts of surfactant per surface area reducing this pressure
  • Large alveoli have a lower pressure inside them but more surface area for surfactant to spread across. This makes surfactant is less effective in larger alveoli and therefore does not lower surface tension as much.
  • This makes pressures equal between different sized alveoli and stops little alveoli collapsing
18
Q

What is respiratory distress syndrome?

A
  • Occurs in premature neonates
  • Too little surfactant
  • Lungs are very stiff (low compliance) and there are few large alveoli (boullae)
  • This causes comprimise of breathing and gas exchange
  • Can happen to adults after major trauma
19
Q

Why is the air in the airways at a low resistance even though they are narrow lumen?

A

-Arranged in parallel so overall resistance is low

20
Q

Where in the normal respiratory tract is the highest resistance?

A

-Trachea and larger bronchi

21
Q

Why does residual volume occur?

A
  • During expiration intrathoracic pressure rises and compresses the lung
  • The small airways are narrowed and resistance increases dramatically
  • Air becomes trapped in the alveoli
22
Q

What effect does obstructive airway disease have on inspiration/expiration?

A
  • When the small airways are narrowed by disease (emphysema/chronic bronchitis) inspiration is okay as the airways are expanding and resistance is lowered
  • But expiration becomes difficult as the resistance is increased much earlier and more air becomes trapped within the lungs
23
Q

How much pleural fluid in pleural space?

A

-10 to 20 ml