Lung Mechanics 2 #1 Flashcards
What is movement of air through the airways driven by?
P gradient between mouth + alveoli
What is the formula for flow?
change in P/R
What is needed for air to flow out quickly?
low R
What is the formula for airway R?
alveolar P - mouth P / airflow at mouth
What is elastic R (stiffness) usually measured as?
compliance (stretchiness)
What is needed to stretch the lung + why?
work needed as lung nat has elastic coil inwards
What is the formula for lung compliance?
change in lung vol/change in transmural P gradient
How does change in lung vol differ between compliant + stiff lung?
- compliant: not much P for change in lung vol
- stiff: need more distending P harder work needed to change lung vol
What happens to compliance of stiff lung?
- change v/change P ratio dec due to inc P
- compliance dec if need higher P change to get change in vol
What is formula for transmural P gradient?
alveolar P - intrapleural P
What does alveolar P equal if there is no airflow?
0 - equal to atmospheric
How can intrapleural P be measured?
with an oesophageal balloon as its same as oesphageal P
How is tidal vol measured?
- 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
What can a static P-V loop show?
compliance as measuring changes in lung vol/changes in P
When does lung have low compliance?
high + low lung vol
What is transmural P?
- distending P of lung
- +ve when you breathe in
Describe P + V from RV to FRC
- v. low vol + compliance
- need to gen lots of TMP to get small vol change
Describe P + V from FRC to TV
- small inc in TMP cause large inc in TV therefore lung v. compliant which is in normal breathing circumstances
When is compliance at its max + sig?
- normal TV
- usually breathing at most compliant part of lung
Describe P + V at TLC
- high vol
- v. hard to breathe as compliance low at this point despite inc TMP, gen little vol + flow
Why are the P-V curves for exp + insp diff?
- at any given TMP, lung has higher vol at exp than insp
- why exp curve slightly higher
What is shape of P-V curves?
sigmoid
What is typical value of lung compliance in adult male?
1.5l.kPa-1 (varies acc to size of indiv)
What is consequence of having stiff lungs?
- low compliance
- high elastic R
- diff to lungs to expand + always want to spring back to small voll all of the time
What are characteristics of lung fibrosis + what causes it?
- stiff/scarred lung
- low compliance
- caused by asbestos exposure, tumors, aspergilus etc
What are characteristics of emphysema?
- elastic tissue destruction
- floppy lung
- high compliance
What is gross pathology shown by lung fibrosis?
- honeycomb appearance
- fibrous tissue + inflammatory cells
What is centrilobar emphysema?
- rel normal alveoli around outside
- destruction of lobules in centre
What is COPD?
- chronic bronchitis = inflamm + excess mucus of airways
- emphysema = alveolar mem break down
What is consequence of COPD?
- inc R to exp air flow + cause airflow obstruction
Where does elastic R come from?
- lung tissues - elastin + collagen fibres
- air-fluid interface in alveoli
How can you stretch air-fluid interface?
need to overcome surface tension
What is La Place equation?
P = 2 x surface tension (T)/r
How does bubble compare to small alveoli?
- if P high, T high + R low - bubble wants to collapse in
Describe surface tension between bubble + fluid
- 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
Explain what T between H2O + bubble shows about small alveoli?
- 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
How does small alveolus differ to large one + sig?
- 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
What happens if small alveoli collapses into big one?
- radii change so P1 progessively inc + P2 dec so process speeds up
Which cells prod surfactant?
type II alveolar
What is surfactant?
- mix of phospholipids e.g. phosphatidyl choline + surfactant proteins (SP-A to D)
- lowers T of alveolar lining fluid
