Lung Mechanics 2 #2 Flashcards
How does surfactant lower T of alveolar lining fluid?
- phospholipids have insol FA end + hydrophil end
- therefore float on surface of alveolar lining fluid - gets inbetween H2O mol trying to get close together
- red T of alveoli in prop to surface conc of surfactant on alveoli
What happens to surfactant as alveolus shrinks + result?
- conc inc as mol closer together so T falls
What happens to P in small alveolus as surfactant inc?
- even though r dec, T now lower so P falls + doesn’t rise as alveolus shrinks
What is effect of surfactant on compliance + why?
inc it as now easier to expand lung as stiffness + amount it wants to collapse in dec by dec T
What other effects does surfactant have?
- red tendency for alveoli to collapse - esp effective in small alveoli where surface conc of surfactant v. high
- red tendency to suck fluid into alveoli (transudation) caused by collapsing P
What is neonatal respiratory distress syndrome?
- occurs in premature babies due to inadequate surfactant prod - get stiff lung due to dec compliance + high T
- problems: inc work of breathing due to red compliance + alveolar collapse + transudation due to high T
What is alveoli dependency?
joining of alveoli to each other to resist collapse + keep them open
When do abnormalities of lung compliance occur?
- when either lung parenchyma e.g. scarred in fibritic lung disease/alveolar lining fluid abnormal
List causes of low lung compliance
- lung fibrosis (scarred)
- neonatal resp distress syndrome
List causes of high lung compliance
emphysema (red quantity of lung tissue)
List obstructive lung diseases
- asthma
- chronic bronchitis
- COPD
List restrictive lung diseases
- lung fibrosis
- resp muscle weakness
- phrenic nerve damage
Describe normal resp system
- airways: normal - little to no R so air can flow in + out easily
- alveoli: normal gas exchange
- resp muscles: normal
- normal lung vol
- normal airflow rates
Describe how resp system affected in asthma
- airways: narrowed due to bronchoconstriction bc sm constricts in response to allergen
- mucosal oedema caused by inflamm
- alveoli: normal
- inc R to F due to dec V
Are effects of asthma rev or irrev?
rev as if take away trigger for bronchoconstriction - airway returns to normal
Describe how resp system affected in chronic bronchitis
airways: wall damaged by cig smoke
- hypertrophied glands + mucus prod
- alveoli normal
Describe how resp system affected in emphysema
- airways: poorly supported due to destruction of ISF + elastin
- inc compliance + flabby lung mean likely to collapse which leads to dynamic compression
- muscles: normal
What is overall effect of COPD?
narrow airways impede air flow
Describe how resp system affected in lung fibrosis
- airways: normal
- alveoli stiff due to fibrosis (scar tissue)
- resp muscles normal
- lung poorly compliant + need work to expand them
Describe how resp system affected in resp muscle weakness
- airways: normal
- alveoli: normal
- resp muscles: weak - can’t expand chest wall + therefore lung
How is airway + high airway R measured?
- airway R measured using body plethysmograph
- high airway R measured using forced exp manoeuvres
What are the forced exp manoeuvres + purpose?
- peak flow l.min-1
- forced exp vol vs time (FEV1, FVC)
- indirect assessment of airway R
What does peak flow measure?
measures peak exp flow rate (how quick blow into it)
How does airway obstruction affect peak flow?
causes low peak flow rate as have inc R to F in airways
What is FEV1 + FVC?
FEV1: - forced exp vol over 1 sec
- measures total amount of air in 1 breath
FVC: forced vital capacity - measures vol breathed in + out over time
How is FEV1 affected in restrictive lung disease?
small as can’t breathe out if you can’t breathe in
What must indiv due in both lung tests?
breathe in to TLC + breathe out as hard + fast as poss
Why are forced exp spirograms (vol vs time) esp useful?
pattern of changes of FEV1 + FVC help distinguish between obstructive + restrictive lung disease
What should normal forced exp ratio be?
- FEV1: 4l after 1 sec
- FVC: 5l after 6 secs
- FEV1/FVC = 4/5 = 80%
- breathe out 75-80% of VC in 1 sec of forced exp so ratio should be >75% in healthy people
What is forced exp ratio in obstructive disease?
- FEV1: 1l (v.low) - breathing out more slowly due to narrow tubes
- FVC: 4l (dec) or 5l (normal)
- FEV1/FVC = 1/4 = 25% - vol of air breathed out in 1 sec much less than 75%
How + why does forced exp ratio change in obstructive disease?
- dec
- air moving through airways more slowly + can;t breathe it out due to inc R
How + why does forced exp ratio change in restrictive disease?
FEV1: 2l (low) - dec as total vol dec
FVC: 2.5l (dec)
FEV1/FVC = 2/2.5 = 80% = normal ratio
- higher than 75% as can’t breathe in v. much + therefore can’t breathe v. much
What is appearance of max F-V loop in obstructive disease of smaller airways?
concave appearance of forced exp curve
How do forced insp + exp flow differ in obstructive disease of smaller airways?
- forced insp flow affected less than forced exp flow
- as narrowing of airways + small airways dec F during exp
What are low peak flow rates related to in restrictive lung disease?
low vol not F in limitation of airway
Does asthma affect compliance?
No as airways affected + not alveoli/tissue
What does stiffness of lung affect?
- ease with which lungs can be inflated
- vol in lungs when muscles are relaxed i.e. FRC which occurs when inward recoil of lungs exactly balances out outward recoil of chest wall
How is recoil of lungs + chest wall diff in disease?
- inward recoil of lungs high in fibrosis
- outward recoil of chest high at low lung vol
How does lung fibrosis affect FRC?
- stiff lung - inc lung recoil - red FRC as it springs in too quickly
- chest wall also at low vol + that’s when its got max outward recoil as well
How does lung fibrosis affect FRC?
- tissue loss - floppy lungs - red lung recoil - inc FRC (barrel chest) - inc chest diameter
- point at lung chest settles at resting vol is point at which there’s not much outward recoil of chest either which is at high vol
How does resp muscle weakness affect FRC?
- 2 recoils of lung + chest wall normal so FRC normal
