Week 2 - Lung mechanics

Question 1

What is a pneumothorax?

Answer 1

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

Question 2

Upon inspiration, what happens to the intrathoracic pressure?

Answer 2

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

Question 3

During expiration what happens to the intrathoracic pressure?

Answer 3

-increase due to decreased lung volume

Question 4

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

Answer 4

-Nothing it always remains negative to outside

Question 5

Why do the abdominal muscles help in forced expiration?

Answer 5

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

Question 6

What is lung compliance?

Answer 6

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

Question 7

What happens to compliance in emphysema and why?

Answer 7

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

Question 8

What happens to compliance in fibrosis and why?

Answer 8

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

Question 9

What causes elastic recoil of lungs?

Answer 9

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

Question 10

What is surface tension?

Answer 10

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

Question 11

What reduces surface tension in alveoli? how?

Answer 11

• Surfactant

- Disrupts interactions between surface molecules

Question 12

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

Answer 12

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

Question 13

What is laplace’s law?

Answer 13

-Pressure = (2xsurface tension)/radius

Question 14

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

Answer 14

-Decreases

Question 15

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

Answer 15

-Increases

Question 16

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

Answer 16

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

Question 17

How does surfactant prevent smaller alveoli collapsing?

Answer 17

• 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

Question 18

What is respiratory distress syndrome?

Answer 18

• 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

Question 19

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

Answer 19

-Arranged in parallel so overall resistance is low

Question 20

Where in the normal respiratory tract is the highest resistance?

Answer 20

-Trachea and larger bronchi

Question 21

Why does residual volume occur?

Answer 21

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

Question 22

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

Answer 22

• 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

Question 23

How much pleural fluid in pleural space?

Answer 23

-10 to 20 ml