Lung Mechanics 2 #1

Question 1

What is movement of air through the airways driven by?

Answer 1

P gradient between mouth + alveoli

Question 2

What is the formula for flow?

Answer 2

change in P/R

Question 3

What is needed for air to flow out quickly?

Answer 3

low R

Question 4

What is the formula for airway R?

Answer 4

alveolar P - mouth P / airflow at mouth

Question 5

What is elastic R (stiffness) usually measured as?

Answer 5

compliance (stretchiness)

Question 6

What is needed to stretch the lung + why?

Answer 6

work needed as lung nat has elastic coil inwards

Question 7

What is the formula for lung compliance?

Answer 7

change in lung vol/change in transmural P gradient

Question 8

How does change in lung vol differ between compliant + stiff lung?

Answer 8

• compliant: not much P for change in lung vol

- stiff: need more distending P harder work needed to change lung vol

Question 9

What happens to compliance of stiff lung?

Answer 9

• change v/change P ratio dec due to inc P

- compliance dec if need higher P change to get change in vol

Question 10

What is formula for transmural P gradient?

Answer 10

alveolar P - intrapleural P

Question 11

What does alveolar P equal if there is no airflow?

Answer 11

0 - equal to atmospheric

Question 12

How can intrapleural P be measured?

Answer 12

with an oesophageal balloon as its same as oesphageal P

Question 13

How is tidal vol measured?

Answer 13

• spirometer
• breathe in from RV to TLC in steps
• at each step as hold breath, measurements of vol inspired + Ppl recorded + used to construct static P-V loop

Question 14

What can a static P-V loop show?

Answer 14

compliance as measuring changes in lung vol/changes in P

Question 15

When does lung have low compliance?

Answer 15

high + low lung vol

Question 16

What is transmural P?

Answer 16

• distending P of lung

- +ve when you breathe in

Question 17

Describe P + V from RV to FRC

Answer 17

• v. low vol + compliance

- need to gen lots of TMP to get small vol change

Question 18

Describe P + V from FRC to TV

Answer 18

• small inc in TMP cause large inc in TV therefore lung v. compliant which is in normal breathing circumstances

Question 19

When is compliance at its max + sig?

Answer 19

• normal TV

- usually breathing at most compliant part of lung

Question 20

Describe P + V at TLC

Answer 20

• high vol

- v. hard to breathe as compliance low at this point despite inc TMP, gen little vol + flow

Question 21

Why are the P-V curves for exp + insp diff?

Answer 21

• at any given TMP, lung has higher vol at exp than insp

- why exp curve slightly higher

Question 22

What is shape of P-V curves?

Answer 22

sigmoid

Question 23

What is typical value of lung compliance in adult male?

Answer 23

1.5l.kPa-1 (varies acc to size of indiv)

Question 24

What is consequence of having stiff lungs?

Answer 24

• low compliance
• high elastic R
• diff to lungs to expand + always want to spring back to small voll all of the time

Question 25

What are characteristics of lung fibrosis + what causes it?

Answer 25

- stiff/scarred lung - low compliance - caused by asbestos exposure, tumors, aspergilus etc

Question 26

What are characteristics of emphysema?

Answer 26

- elastic tissue destruction - floppy lung - high compliance

Question 27

What is gross pathology shown by lung fibrosis?

Answer 27

- honeycomb appearance | - fibrous tissue + inflammatory cells

Question 28

What is centrilobar emphysema?

Answer 28

- rel normal alveoli around outside | - destruction of lobules in centre

Question 29

What is COPD?

Answer 29

- chronic bronchitis = inflamm + excess mucus of airways | - emphysema = alveolar mem break down

Question 30

What is consequence of COPD?

Answer 30

- inc R to exp air flow + cause airflow obstruction

Question 31

Where does elastic R come from?

Answer 31

- lung tissues - elastin + collagen fibres | - air-fluid interface in alveoli

Question 32

How can you stretch air-fluid interface?

Answer 32

need to overcome surface tension

Question 33

What is La Place equation?

Answer 33

P = 2 x surface tension (T)/r

Question 34

How does bubble compare to small alveoli?

Answer 34

- if P high, T high + R low - bubble wants to collapse in

Question 35

Describe surface tension between bubble + fluid

Answer 35

- T at interface between bubble (air) + fluid - H2O mol attracted to each other more than to air - H2O mol get v.close together to dec SA so as close together as poss at air-H2O interface - as H2O tries to get v.close - shrinks down + gen inward P + bubble shrinks

Question 36

Explain what T between H2O + bubble shows about small alveoli?

Answer 36

- bubble in water wants to occupy smallest vol poss so it can be as close as poss to other bubbles and therefore gen inward P inside it - P inc if T high + R low - bubble wants to collapse in - small alveoli with high T more likely to have high collapsing P

Question 37

How does small alveolus differ to large one + sig?

Answer 37

- small r so greater collapsing in P than big one - big alveoli has big r so P small - small will want to collapse into big as a result which don't want

Question 38

What happens if small alveoli collapses into big one?

Answer 38

- radii change so P1 progessively inc + P2 dec so process speeds up

Question 39

Which cells prod surfactant?

Answer 39

type II alveolar

Question 40

What is surfactant?

Answer 40

- mix of phospholipids e.g. phosphatidyl choline + surfactant proteins (SP-A to D) - lowers T of alveolar lining fluid