Work of ventilation 1

Question 1

work required to move the lung and chest wall

Answer 1

P X /_\ V

Question 2

what muscles do all the work in normal breathing and why

Answer 2

inspiratory muscles

expiration is passive

Question 3

minute volume and units

Answer 3

respiratory rate per minute x tidal volume

Question 4

how can any given ventilation be achieved

Answer 4

a high tidal volume & lower rate

a lower tidal volume but higher rate

Question 5

optimum value of respiratory rate to minimise to work

Answer 5

15/min

Question 6

optimum value of rtidal volume to minimise to work

Answer 6

500ml

Question 7

compliance

Answer 7

measure of the ease with which the lungs can be stretched or inflated.
CL = ΔV / ΔP
ΔV : change in lung volume
ΔP: change in transmural pressure

Question 8

transmural pressure

Answer 8

difference in pressure in alveoli and pressure in pleural cavity

Question 9

how does the increased elastic resistance change optimal respiratory rate and tidal volume

Answer 9

increased work needed for total volume

increased respiratory frequency

Question 10

how does the increased airway resistance change optimal respiratory rate and tidal volume

Answer 10

even more work needed for total volume

decreased respiratory frequency

Question 11

name the 2 types of works of breathing

Answer 11

Compliance (Elastic) Work:
1. Force to expand lung against its elastic properties
Frictional/Resistive Work:
2. Force to overcome air-flow resistance

Question 12

name the 3 types of compliance

Answer 12

Static compliance
Dynamic compliance
Specific compliance

Question 13

static compliance

Answer 13

is measured when there is no airflow (airway resistance does not contribute)

Question 14

dynamic compliance

Answer 14

is measured during airflow (Hysteresis loop)

Question 15

specific compliance

Answer 15

measures elastic properties (corrects for lung volume)

Question 16

relationship between volume change (ΔV) and pressure change (ΔP) during quiet breathing

Answer 16

Hysteresis

Question 17

increased compliance is caused by … and is a symptom of ..

Answer 17

Loss of elastin fibres/elastic tissue in early emphysema or ageing

Question 18

decreased compliance is caused by … and is a symptom of ..

Answer 18

Chest wall compliance: scoliosis, ankylosing spondylitis

Pulmonary fibrosis

Question 19

how is elastance related to compliance

Answer 19

inversely

measure of snap back or elastic recoil

Question 20

how is emphysema related to compliance and elastance

Answer 20

increased compliance - loss of elastin fibres

decreased elastance

Question 21

how is fibrosis related to compliance and elastance

Answer 21

decreased compliance, increased elastance

Question 22

tissue elasticity

Answer 22

Energy (ATP) is required to deform elastic tissues (stretch elastin fibers and overcome surface tension)

Question 23

how is the work of tissue elasticity stored

Answer 23

as potential energy

Question 24

surface tension

Answer 24

Water molecules are more attracted to each other than to air, creating a surface tension.
Surface tension contributes to minimising the surface area of alveoli

Question 25

what alleviates surface tension

Answer 25

surfactant

Question 26

what can surface tension lead to

Answer 26

alveolar and lung collapse

Question 27

high surface tension leads to

Answer 27

low compliance

Question 28

surfactant consists of

Answer 28

10% surfactant specific proteins (SPA, SPB, SPC, SPD)

90% lipids - phospholipids mainly DPPC (Disaturated palmitoyl phosphatidylcholine)

Question 29

surfactant is synthesised by and when

Answer 29

type II pneumocytes (alveolar cells) between 22-32 weeks gestation

Question 30

where is surfactant stored

Answer 30

Stored in cytoplasmic lamellar bodies until released to surface of alveolus and made available at air-liquid interface

Question 31

function of surfactant

Answer 31

Reduces surface tension by interfering with water molecule interactions
increases compliance of the lung
Important role also in stabilising alveoli of different sizes

Question 32

what does laplaces relate to

Answer 32

pressure to surface tension and radius

small radius = high pressure

Question 33

law of laplace

Answer 33

pressure = 2 x surface tension/radius of alveolus

Question 34

how does surfactant change surface tension and pressure

Answer 34

surface tension is no longer constant

alveoli of different radius and pressures can now have the same pressure

Question 35

where do the surfactant molecules position themselves?

Answer 35

position at air-liquid interface with hydrophobic fatty acid chains projecting into alveolar air and hydrophyllic end into the fluid lining of the alveolus.

Question 36

when is surface tension lowering effect at its greatast

Answer 36

as alveoli become smaller in expiration as concentration of surfactant increases at air-liquid interface.

Question 37

how does surfactant change surface tension and when

Answer 37

differentially reduces surface tension in alveoli, more at lower volumes and less at higher volumes leading to alveolar stability and co-existence of large and small alveoli

Question 38

newborn respiratory distress syndrome

Answer 38

Developing foetal lungs do not normally synthesise surfactant until late in pregnancy.
Therefore, premature infants may not have enough pulmonary surfactant and struggle to breathe.

Question 39

treatment of newborn respiratory distress syndrome

Answer 39

Stimulated by corticosteroids given to mother prior to delivery of premature infant
Oxygen through continuous positive airway pressure
Survanta (surfactant)

Question 40

surface tension definition and its importance in the lungs

Answer 40

the force exerted by water molecules on the surface of the lung tissue as those water molecules pull together.
.As the air inside the lungs is moist, there is considerable surface tension within the tissue of the lungs.