elasticity and compliance

Question 1

define elasticity

Answer 1

resistance to deformation/stretch by an external force (stiffness)
-ability to recoil

Question 2

define compliance

Answer 2

ability to stretch
-inverse of elasticity

Question 3

what does high elasticity mean for compliance

Answer 3

low compliance

Question 4

explain high elasticity with low compliance - resistance band

Answer 4

resistance band has high recoil
snaps back to original shape
difficult to stretch

Question 5

low elasticity = high …….

Answer 5

compliance

Question 6

describe low elasticity with high compliance - resistance band

Answer 6

resistance band had low recoil
returns to original shape but not as rapidly
easier to stretch

Question 7

chest wall pulls …..

Answer 7

outwards

Question 8

lungs pull …..

Answer 8

inwards

Question 9

at rest what is created in the lungs

Answer 9

negative pressure in the pleural cavity

Question 10

how do you calculate lung distending pressure

Answer 10

pressure inside - pressure outside

Question 11

what does lung distending pressure counteract

Answer 11

elastic recoil of lungs

Question 11

what does lung distending pressure prevent

Answer 11

lungs collapsing

Question 11

elastic recoil of lungs - describe

Answer 11

• 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

Question 11

describe the pressure changes in the lungs during inspiration

Answer 11

1. decrease in intrapleural pressure
2. increase in lung volume
3. decrease in alveolar pressure
4. inflow of air

Question 12

symbol for compliance

Answer 12

C

Question 13

lung distending pressure …… during inspiration

Answer 13

increases

Question 14

lung distending pressure during inspiration - describe

Answer 14

• 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

Question 15

lung compliance curves - explain

Answer 15

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

Question 16

why are lung compliance curves s-shaped

Answer 16

at high vols - lung compliance is low

at normal vols - high

low vols - low

Question 17

what are the determinants of lung compliance

Answer 17

elastic properties of the tissue
surface tension

Question 18

what is surfactant used for

Answer 18

alleviating surface tension

Question 19

surfactant lines ……

Answer 19

air-water interfaces

Question 19

what are mothers given to produce surfactant in premature babies

Answer 19

a steroid shot

Question 19

c

Answer 19

• 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

Question 20

what effect does surfactant have on lung compliance

Answer 20

decreases it

Question 21

describe the elastic recoil of the lungs + chest wall

Answer 21

lungs pull inwards chest wall pulls outwards

Question 22

chest wall distending pressure at functional residual pressure

Answer 22

counteracts elastic recoil of chest wall prevents chest wall from springing outwards

Question 22

what 2 sources restrict the chest wall

Answer 22

extrinsic intrinsic

Question 23

examples of intrinsic sources that restrict chest wall compliance

Answer 23

scoliosis kyphosis ankylosing spondylitis pectus excavatum

Question 24

why are the chest wall + lungs not isolated

Answer 24

due to the pleural fluid linkage

Question 25

chest wall and lungs are equally compliant - explain

Answer 25

- 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