Lecture 3 - Mechanics of breathing 2

Question 1

What is functional residual capacity

Answer 1

ERV+RV
It is the volume of air present in the lungs after passive expiration. opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the diaphragm or other respiratory muscles. usually around 2500 ml.

Question 2

What is compliance

Answer 2

how distensible the lung is

Question 3

What effects inflation/ distensibility of the lung

Answer 3

tissue elastic forces (collagen and elastin) and surface tension. increase in either would make it harder for the lungs to inflate

Question 4

What is surface tension

Answer 4

forces in alveoli that try to collapse the bubble

Question 5

What is elastence

Answer 5

property of

Question 6

Relationship between introthoracic pressure and lung volume during tidal breathing

Answer 6

during inspiration, the intrathoracic pressure becomes more negative as lung volume increases
during expiration, intrathoracic pressure increases (becomes less negative) and volume decreases.

Question 7

What would happen in a perfect elastic system

Answer 7

there would be a linearity in the curve

Question 8

What causes the hysteresis loop? what does it define

Answer 8

the elastic resistance of the tissues - collagen, elastin etc
it defines the work required to actually breathe

Question 9

Hysteresis

Answer 9

takes energy from outside to increase energy of the machine.
difference between heat produced when you expand elastic band and the heat released when you contract it is hysteresis.
as you breath out passive process, as you breathe in active process.
difference in heat is hysteresis.

Question 10

Why does hysteresis occur?

Answer 10

because of the elastic nature of the tissues

Question 11

What is compliance

Answer 11

the elasticity of the lungs. Compliance is defined as the change in volume/the change in pressure

Question 12

How do you measure compliance?

Answer 12

it is dynamic not static.
measure spirometry for volume.
oesophageal balloon for pressure. place it in intrathoracic compartment. these values a relative (changes in pressure)

Question 13

What happens in a lung compliance curve during expiration

Answer 13

during expiration
alveolar pressure is 0 and pleural pressure is -3.
there is a negative pressure that holds your lungs out and stops them from collapsing
recoil pressure is +3

Question 14

What happens in a lung compliance curve at the end of expiration

Answer 14

as lungs start expanding outwards, the negative pressure in the lungs start increasing and alveolar pressure becomes -5. recoil pressure( pressuring opposing it) is +5. not much increase in volume

Question 15

What happens in a lung compliance curve at peak inspiration

Answer 15

as you take a deep breath in, the recoil pressure of the lungs increases by 30. takes you up to total lung capacity. chest wall moves out, diaphragm moves out, intrapleural pressure goes to about -30.

Question 16

How is the compliance curve formed

Answer 16

the links between the various recoil pressures between expiration and inspiration forms the curve. from high to low compliance

Question 17

High compliance is?

Answer 17

for a little change in pressure you get quite a lot of change in volume

Question 18

Low compliance

Answer 18

Massive amounts of change in pressure for a change in lung volume

Question 19

Chest wall compliance

Answer 19

has its own compliance
wants to spring outwards.
pressure exerted by the chest wall

Question 20

after maximal expiration

Answer 20

chest wall has a recoil pressure of -30. glottis is closed, muscles are relaxed

Question 21

as you start to breathe in

Answer 21

small change in volume, open glottis, muscles still relaxed
large change in pressure
-30 to -5 when only 25% of expansion has occurred

Question 22

during maximal inspiration,

Answer 22

large change in volume, close glottis, relax muscles
however small change in pressure from -5 to -3. high compliance lung. lung finding it harder to expand requires more pressure.

Question 23

chest wall curve and lung compliance curve

Answer 23

superimpose on eacother

Question 24

How do you determine FRC from a compliance curve

Answer 24

FRC is the relaxation point of the resp system when chest wall and lung pressures are equal but opposite (eg. -5 and +5) There is a neutral point on the curve that indicates it. defines end of quiet breathing.
lungs are in equilibrium.

Question 25

During anesthesia, patients lungs collapse to what point?

Answer 25

so that they are in equilibrium, at FRC neutral point.

Question 26

Which diseases reduce compliance

Answer 26

Pulmonary fibrosis
elastic tissue is replaced with fibrous tissue - more rigidity.
needs a lot of increase in pressure for a little change in volume.

Question 27

What is kyphoscoliosis

Answer 27

deformed chest wall. difficult to increase and decrease the lung. decreases lung compliance.

Question 28

circumferential thoracic burn

Answer 28

skin when burnt loses elasticity and effects compliance as it makes it difficult to breathe.

Question 29

Diseases that increase compliance

Answer 29

emphysema
destroys actual structure of lung from inside. left with air spaces and pockets and so there is reduced elasticity. thoracic outward forces take over, massive lung expansion.
lost all alveoli so become hypoxic.

Question 30

ventilation and blood at different parts of the lung

Answer 30

role of gravity.
top of lungs - lots of ventilation
not much blood. middle of lung, some ventilation and some blood. at the bottom, lots of blood (due to gravity), little ventilation

Question 31

Why is compliance not equal throughout the lung?

Answer 31

changes of gas exchange throughout the lung. gravity changes compliance.
lot easier to open lungs at the top - high compliance
low compliance at the bottom - as more blood
when lying down - lung pools at the back. marginally reduces when supine
better lying the other way

Question 32

What happens to Closing capacity as you get older

Answer 32

as you get older closing capacity increases, higher tendency for lungs to close, alveoli close shut. lot of energy to reopen alveoli.

Question 33

What is closing capacity

Answer 33

that volume in the lungs at which below alveoli will start to collapse. closing capacity is well below FRC normally.

Question 34

What happens when closing capacity exceeds Functional residual capacity

Answer 34

dependent lung regions will be poorly ventilated

Question 35

What does the force exerted by a sphere (alveoli) depend on

pulmonary compliance and alveoli

Answer 35

its radius. smaller balloon will push out air faster than bigger balloon. smaller will empty out into bigger as they will exert more pressure.

Question 36

What is the law of laplace

Answer 36

pressure exerted on the wall of a sphere is 2t/r smaller the radius, bigger the pressure

Question 37

Describe surface tension in the lung

Answer 37

lungs are lined with water. causes surface tension. oxygen dissolves in it.

Question 38

How is surface tension present in the lung

Answer 38

energy is required to maintain the gas-liquid interface. Potential energy is minimised through reducing surface area to volume ratio by forming a sphere

Question 39

What is on the alveolar lining?

Answer 39

surfactant - detergent which reduces surface tension of water so oil can mix with water.

Question 40

What is surfactant? what is it produced by? what is it made of?

Answer 40

produced by type 2 alveolar cells
90% phospholipid
10% protein
acts as a detergent to reduce alveolar surface tension.

Question 41

What is the function of surfactant?

Answer 41

increases pulmonary compliance
prevents atelactasis - lung collapse
aids alveolar recruitment
minimses alveolar fluid

Question 42

In what condition is surfactant deficient

Answer 42

infant respiratory distress syndrome

Question 43

What does surfactant do in terms of laplace law

Answer 43

instead of collapsing smaller alveoli, larger alveoli and smaller alveoli equally empty out into eachother and pressure equalises.
surfactant becomes more dispersed as alveolar volume increases to try and reduce it.

Question 44

Describe work of breathing in terms of potential energy

Answer 44

energy used in inspiration to overcome elastic forces is stores as potential energy which is dissipated in expiration
work - expended in the form of heat to overcome resistance forces

Question 45

work calculation

Answer 45

in terms of hysteresis loop

volume x pressure

Question 46

types of airflow

Answer 46

laminar flow - energy efficient - move in the same direction - low resistance
turbulent flow - in different directions

Question 47

Most of upper airways has what sort of flow?

Answer 47

turbulent flow because they are huge airways with huge volumes
lower - more laminar

Question 48

low and high reynoids number

Answer 48

low - laminar

high - turbulent

Question 49

minimal work during breathing
during rest?
at hyperventilation?
during restrictive conditions?
in obstructive conditions?

Answer 49

rest - 2-5% expenditure
at max hyperventilation - 30% of energy expenditure
restrictive conditions - work minimised with rapid small breaths
obstructive - work maximised with large volume slow breaths

Question 50

breath sounds in large airways and over lungs

Answer 50

in large airways - turbulent

over lungs - distal airways - less turbulent