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Module 103: The Heart, Lungs and Blood > Theme 4: Lecture 1 - Mechanics of breathing > Flashcards

Theme 4: Lecture 1 - Mechanics of breathing Flashcards

1
Q

Compliance

A

Stretchiness of lungs

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2
Q

What is elastic recoil balanced by

A

Chest wall tendency to recoil in the opposite direction

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3
Q

What happens regarding pressures at the end of quiet expiration

A

The pressures balance

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4
Q

What are the inspiratory muscles

A
  • Diphragm (75% of change in volume)
  • External intercostals
  • Accessory muscles (Scalene and sternomastoids)
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5
Q

Describe the process of inspiration

A
  • Contraction of inspiratory muscles increases intrathoracic volume
  • This causes a decrease in intrapleural pressure (usually -2.5 -6 mmhg)
  • Lungs are pulled into more expanded position and the pressure in the airways becomes negative. Air moves in (Patm>Palv)
  • At end of inspiration pressures are equal
  • Recoil of lungs and chest wall then occur
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6
Q

Is inspiration an active or passive process

A

Active

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7
Q

Is expiration an active or passive process

A

Generally passive

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8
Q

Trans pulmonary pressure

A
  • The chest wall exerts a distending pressure on the pleural space, which is transmitted to the alveoli to increase its volume, lower its pressure, and generate airflow inwards
  • It is the difference between the alveolar pressure and the intrapleural pressure in the pleural cavity
  • This distending pressure is called the trans pulmonary pressure (Ptp).
  • Chest wall expansion is done by muscles
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9
Q

Relationship between transpulmonary pressure and elastic reocoil

A

For a given lung volume, the transpulmonary pressure is equal and opposite to the elastic recoil pressure of the lung.

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10
Q

Elastic recoil

A

The recoil on exhalation

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11
Q

Tidal volume (TV)

A

Normal breathing

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12
Q

Functional residual capacity (FRC)

A

The volume remaining in the lungs after a normal passive exhalation

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13
Q

Expiratory reserve volume (ERV)

A

the volume of extra air, above-normal volume, exhaled during a forceful breath out

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14
Q

Inspiratory capacity (IC)

A

The amount of air that can be inspired in a deep breath in

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15
Q

Vital capacity (VC)

A
  • the maximum amount of air a person can expel from the lungs after a maximum inhalation.
  • Inspiratory reserve volume plus tidal capacity plus expiratory reserve volume
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16
Q

Residual volume (RV)

A

The volume of air left in the lung after a forced expiration

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17
Q

Total lung capacity (TLC)

A

the volume of air in the lungs upon the maximum effort of inspiration

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18
Q

Compliance

A
  • Static measure of lung “stretchiness” (lung and chest recoil)
  • Volume change per unit pressure change
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19
Q

How is compliance different to resistance

A

Compliance is a static measure whereas resistance is dynamic, accounting for airflow resistance

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20
Q

What is the balance point of compliance

A
  • Where the lung and chest are in equilibrium after exhaling
  • Functional residual capacity
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21
Q

Why do lungs always tend to collapse

A

Transpulmonary pressure is positive from residual volume to total lung capacity so the lungs always tend to collapse

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22
Q

What is positive pressure

A
  • a pressure within a system that is greater than the environment that surrounds that system
  • therefore if there is a leak, gas will leak out into the surrounding environment
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23
Q

What is negative pressure

A
  • a pressure within a system that is lower than the environment that surrounds the system
  • Therefore if there is a leak, gas will get sucked into the system
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24
Q

Describe the lungs like a spring

A

The lungs are like a spring that can only be stretched

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25
Q

Describe the chest wall like a spring

A

The chest wall is like a spring which can be compressed or distended

26
Q

Why does the chest wall tend to collapse

A

Transthoracic pressure is negative at residual volume and functional residual volume so the chest wall tends to spring out

27
Q

What is transthoracic pressure

A
  • The transthoracic pressure gradient is the difference between the pressure in the pleural space and the pressure at the body surface
  • represents the total pressure required to expand or contract the lungs and chest wall.
28
Q

What does lung compliance depend on

A
  • How inflated the lungs are

- Lungs are less compliant at higher volumes

29
Q

What is the difference in compliance curves for inspiration and expiration called

A

Hysteresis

30
Q

Describe lung compliance in emphysema

A
  • In emphysema the P-V curve demonstrates lungs with increased compliance
  • ‘Loss of elastic recoil therefore easy to inflate, but difficult to exhale’
31
Q

Describe lung compliance in pulmonary fibrosis

A
  • In pulmonary fibrosis the P-V curve demonstrates stiff lungs
  • ‘Increase in elastic recoil therefore difficult to inflate the lungs’
32
Q

Compliance equation

A

change in volume divided by change in pressure

33
Q

Describe the process of exhalation

A
  • Exhalation occurs when the distending pressure is released
  • Built up potential in the form of increased elastic recoil leads to passive relaxation of alveoli leads to decrease in alveolar volume leads to increase in Palv (to be > Patm) leads to outward air flow
34
Q

When does active exhalation occur

A

Active exhalation occurs when expiratory respiratory muscles are engaged, but short of exercise and disease, we don’t usually need to call upon these

35
Q

What impairs efficient and effective exhalation

A

Loss of elastic recoil

36
Q

Describe surface tension

A
  • Cohesive forces between molecules
  • Molecules on the surface have no atoms above them which results in stronger attractive forces on nearest neighbours on the surface
  • Liquid surface area becomes as small as possible i.e. sphere
37
Q

What does surface tension do to the alveolus

A

Tends to collapse the alveolus

38
Q

What does surface tension increase with

A

Emphysema and age

39
Q

What does surfactant do

A

Reduces surface tension

40
Q

Which cells make surfactant

A

Type II alveolar cells

41
Q

What is the major component of surfactant

A

Dipalmitoyl phosphatidylcholine

42
Q

How do type II alveolar cells make surfactant

A

By extracting fatty acids from the blood

43
Q

How does surfactant reduce surface tension

A
  • Hydrophilic and hydrophobic ends repel each other and interfere with liquid molecule attraction
  • Lowers surface tension
44
Q

What does Laplace’s law tell us

A

It tells us that pressure in a spherical compartment is:

  • proportional to the tension and,
  • inversely proportional to the radius of that sphere
45
Q

infant/neonatal respiratory distress syndrome

A
  • Premature babies (< 30 weeks) have surfactant deficiency

- are at risk for infant/neonatal respiratory distress syndrome from “alveolar collapse” due to high surface tension

46
Q

Why is surfactant important

A
  • Increases lung compliance (because surface forces are reduced)
  • Promotes alveolar stability
  • Prevents alveolar collapse (small alveoli are prevented from getting smaller, large alveoli are prevented from getting bigger)
  • Surface tension tends to suck fluid from capillaries into alveoli (reduction of surface tension reduces hydrostatic pressure in tissue outside capillaries and keeps lungs dry)
47
Q

What does airway resistance originate from

A

Friction between air and mucosa

48
Q

Airway resistance equation

A

Pressure difference between alveoli and mouth divided by the flow rate

49
Q

What is pulmonary resistance the sum of

A

Total tissue resistance and airway resistance

50
Q

What causes tissue resistance

A

Lung and chest wall sliding over each other

51
Q

What happens to the cross section as you go further down into the small airways

A

Increases a lot (trumpet shaped graph)

52
Q

What does Reynold’s number predict

A

Helps predict when laminar flow converts to turbulent flow

53
Q

Describe laminar flow

A

Laminar flow is smooth flow. Resistance generated is proportional to the radius (r4).

54
Q

Describe turbulent flow

A

Turbulent flow is irregular, chaotic, with eddie currents. It’s good for transferring heat (radiators try to enhance turbulent flow), but the resistance is high

55
Q

Factors affecting airway resistance

A
  • Inflammation
  • Mucus
  • Bronchodilators
  • Steroids
  • Gas density
56
Q

What is the work of breathing

A

Work required to stretch elastic tissues of chest wall and lungs , moving inelastic tissues and air through tubes
It is the amount of energy or O2 consumption needed by the respiratory muscles to produce enough ventilation and respiration to meet the metabolic demands of the body.

57
Q

What causes greater work of breathing due to elastic work

A

Decreased elasticity in restrictive diseases

58
Q

What causes greater work of breathing due to non elastic work

A

Obstructive diseases lead to greater work of breathing to overcome increased airway resistance

59
Q

Poiseuille’s equation

A
  • Resistance to flow is described by this law
  • Resistance = (8 x viscosity x length)/(pi x radius to the power 4)
  • Resistance is inversely proportional to the 4th power of the radius
  • Flow is inversely proportional to the viscosity of the fluid
  • ‘It’s hard to squeeze honey through a long thin tube’
60
Q

Why does airway resistance decrease as you go down into the smaller airways even though the radius of the airways is decreasing

A
  • There are more airways the further down the generations you go
  • The airways of a given generation are in parallel with each other.
  • All airways in a generation contribute to that generation’s total resistance (Rt)
  • The Rt of a system in parallel will always be less than any individual airway resistance

Module 103: The Heart, Lungs and Blood (51 decks)

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