respiratory: lung mechanics Flashcards
how to measure lung compliance
measure change in volume using spirometer
measure change in intrapleural pressure using oesophageal balloon
where is lung compliance highest and when is it lowest
highest at tidal volume, lowest at TLC and RV
what conditions make lung compliance extra low/extra high
extra low: fibrosis/ neonatal respiratory distress syndrome
extra high: emphysema
what happens in bronchiolitis
thick narrow bronchioles with excess mucus
what contributes to elastic resistance
elastin + collagen
air-fluid interface
surface tension equation, what kind of tendency is there
P= 2T/R
small bubbles likely to collapse into big ones as force of surface tension is inwards
what produces surfactant? what’s in it?
alveolar type II cells
phospholipids + surfactant proteins -> due to amphipathic nature of phospholipids, they float on surface of alveolar fluid lining
what does surfactant do? how does it work
reduce surface tension in proportion to surface conc-> compliance increases,
alveoli doesnt collapse (especially in small alveoli), tendency to suck fluid in drops
as alveolus shirinks-> surfactant surface conc increases-> surface tension decreases-> P falls
what’s neonatal respiratory distress syndrome
premature babies dont produce enough surfacant -> reduced compliance and alveolar collapse
how else do alveoli resist collapse
alveoli join together
obstructive lung disease vs restrictive lung disease
obstructive lung disease: airways not ok/high resistance-> air cant flow down tubes
restrictive lung disease: trouble expanding thoracic vol/cant overcome tendency of lung collapsing inwards eg fibrosis/respiratory muscle weakness/phrenic nerve damage
two conditions of COPD
emphysema and chronic bronchitis
what happens in asthma, chronic bronchitis and emphysema
asthma: bronchoconstriction, mucosal oedema
chronic bronchitis: hypertrophied glands, mucous production, wall damage, narrow airways
emphysema: elastic tissue unable to hold airways open, alveoli destroyed
what happens in lung fibrosis and respiratory muscle weakness
lung fibrosis: stiff alveoli, scar tissue
respiratory muscle weakness: airways and alveoli normal, respiratory muscles weak
ways to measure airway resistance
body plethysmograph
peak flow
forced expiratory vol vs time
whats FEV1 and FVC, whats normal value of FEV1/FVC
FEV1 is forced expiratory vol in 1 sec
FVC is forced vital capacity (total amt u can force out)
normal value is 75%
how are FEV1, FVC and FEV1/FVC values affected in obstructive and restrictive diseases
obstructive: FEV1 low, FVC normal/low, FEV1/FVC low
restrictive: FEV1 low, FVC low, FEV1/FVC normal
how are maximum flow-volume loops affected by obstructive/restrictive lung disease
obstructive: left-ish; concave appearance of forced expiratory curve
restrictive: right-ish, normal shape, peak flow is lower
what happens to FRC in lung fibrosis and emphysema
fibrosis: reduced FRC
emphysema: increased FRC
