elasticity and compliance Flashcards
define elasticity
resistance to deformation/stretch by an external force (stiffness)
-ability to recoil
define compliance
ability to stretch
-inverse of elasticity
what does high elasticity mean for compliance
low compliance
explain high elasticity with low compliance - resistance band
resistance band has high recoil
snaps back to original shape
difficult to stretch
low elasticity = high …….
compliance
describe low elasticity with high compliance - resistance band
resistance band had low recoil
returns to original shape but not as rapidly
easier to stretch
chest wall pulls …..
outwards
lungs pull …..
inwards
at rest what is created in the lungs
negative pressure in the pleural cavity
how do you calculate lung distending pressure
pressure inside - pressure outside
what does lung distending pressure counteract
elastic recoil of lungs
what does lung distending pressure prevent
lungs collapsing
elastic recoil of lungs - describe
- elastic recoil
-lungs pull inwards
-chest wall pulls outwards
- at rest this creates negative pressure in the pleural cavity
-lung volume under these conditions is called functional residual capacity (~2.5L)
- ~0.5kPa relative to atmospheric (P lower B) pressure and alveolar (P lower A) pressure
describe the pressure changes in the lungs during inspiration
- decrease in intrapleural pressure
- increase in lung volume
- decrease in alveolar pressure
- inflow of air
symbol for compliance
C
lung distending pressure …… during inspiration
increases
lung distending pressure during inspiration - describe
- chest wall expands
-small decrease in pressure in lungs
-bigger decrease in pressure in pleural cavity - 0.5kPa - -0.1kPa - -1kPa = +1kPa
-distending pressure increases
lung compliance curves - explain
compliance - change in volume are a result of change in lung distending pressure
-requires more than 1 data point
-slope of line = lung compliance
-compliance INCREASES = small increase in lung distending pressure results in big increase in lung vol
-compliance DECREASES = small increase in lung distending pressure results in small increase in lung vol
why are lung compliance curves s-shaped
at high vols - lung compliance is low
at normal vols - high
low vols - low
what are the determinants of lung compliance
elastic properties of the tissue
surface tension
what is surfactant used for
alleviating surface tension
surfactant lines ……
air-water interfaces
what are mothers given to produce surfactant in premature babies
a steroid shot
c
- surfactant lines air-water interfaces
-water molecules become separated by surfactant molecules
-attractive forces between water molecules decrease
-surface tension DECREASES (10% of the theoretical value:
- secreted by type 2 alveolar cells
- more effective in smaller alveoli
-smaller radius
-surfactant density INCREASES
-all alveoli during expiration
what effect does surfactant have on lung compliance
decreases it
describe the elastic recoil of the lungs + chest wall
lungs pull inwards
chest wall pulls outwards
chest wall distending pressure at functional residual pressure
counteracts elastic recoil of chest wall
prevents chest wall from springing outwards
what 2 sources restrict the chest wall
extrinsic
intrinsic
examples of intrinsic sources that restrict chest wall compliance
scoliosis
kyphosis
ankylosing spondylitis
pectus excavatum
why are the chest wall + lungs not isolated
due to the pleural fluid linkage
chest wall and lungs are equally compliant - explain
- at FRC chest wall distending pressure is negative (-0.5kPa)
- slopes are the same
- but chest wall and lungs are not isolated
- pleural fluid linkage
