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103 Theme 4 - Lungs > Mechanics of breathing, pressure and work > Flashcards

Mechanics of breathing, pressure and work Flashcards

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1
Q

How does inspiration/expiration work?

A
  • Lungs and chest wall elastic structures
  • Lungs are stretched when we inhale (‘stretchiness’ is termed lung compliance)
  • They recoil on exhalation (Term: elastic recoil)
  • This is balanced by the chest wall tendency to recoil in opposite direction
  • At end of quiet expiration pressures balance
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2
Q

What are the inspiratory muscles?

A
  • Diaphragm (75% change in volume)
  • External intercostals
  • bucket-handle
  • Accessory muscles
  • scalene
  • sternomastoids
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3
Q

How does inspiration work?

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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4
Q

Which part of the graph is inhalation and which part is exhalation?

A
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5
Q

What is transpulmonary 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
  • This distending pressure is called the trans pulmonary pressure (Ptp).
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6
Q

What anatomical component is responsible for chest expansion?

A

Muscles

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7
Q

Under physiological conditions:

The Ptp is always _______

The Ppl is always ________

A

Positive

Negative

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8
Q

What is Ppl?

A

Note: Ppl is variably called pleural or intrapleural pressure

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9
Q

What is Ptp?

A

Transpulmonary pressure

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10
Q

What is the relationship between transpulmonary pressure and elastic recoil pressure?

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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11
Q

Label which line is Total, Lung and Chest Wall Compliance

A
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12
Q

What graph is this?

A

Lung Compliance (pressure volume curve)

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13
Q

Label each line

A
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14
Q

What does the compliance of the lung depend on?

A

The compliance of the lung depends how inflated or not it is

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15
Q

What is hysteresis?

A

The compliance curves are different for inspiration and exhalation. This difference is called hysteresis (frictional resistance changes)

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16
Q

Is the lung more or less compliant at higher volumes?

A

lung is less compliant at higher volumes

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17
Q

What does each picture show?

A
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18
Q

What is compliance like in normal lung?

A

Compliance is just right. Good compliance for low work of inhalation, and good retention of elasticity of alveolar units to allow effective exhalation.

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19
Q

What is compliance like in interstitial fibrosis?

A

Compliance is decreased due to more stiff alveolar walls from scarring (called fibrosis).

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20
Q

What is compliance like in emphysema?

A

Compliance is increased due to loss of alveolar interdependence.

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21
Q

What does a P/V curve in emphysema show?

A

In emphysema the P-V curve demonstrates lungs with increased compliance

‘Loss of elastic recoil à easy to inflate, but difficult to exhale’

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22
Q

What does a P/V curve in pulmonary fibrosis show?

A

In pulmonary fibrosis the P-V curve demonstrates stiff lungs

‘Increase in elastic recoil -> difficult to inflate the lungs’

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23
Q

Complete the P/V curve labels

A
24
Q

How does exhalation work?

A
  • Exhalation occurs when the distending pressure is released
  • Built up potential in the form of increased elastic recoil -> passive relaxation of alveoli -> decrease in alveolar volume -> increase in Palv (to be > Patm) -> outward air flow
25
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

26
Q

What impairs efficient and effective exhalation?

A

Loss of elastic recoil

27
Q

What is surface tension?

A
  • Cohesive forces between molecules
  • Molecules on the surface have no atoms above them
  • Results in stronger attractive forces on nearest neighbours on the surface
28
Q

How do alveoli collapse?

A
  • Liquid surface area becomes as small as possible i.e. sphere - liquid tends to form spheres because of surface tension pressures
  • Tends to collapse the alveolus
29
Q

What 2 things does surface tension increase with?

A
  • Emphysema
  • Age
30
Q

How is surfactant produced?

A

Type II alveolar cells extract fatty acids from blood and synthesise surfactant

31
Q

What is surfactant made of?

A

Major component is dipalmitoyl phosphatidylcholine (DPPC)

32
Q

What does surfactant cause?

A

Surfactant causes surface tension be low, and also to vary across the respiratory cycle

33
Q

Which alveolus has higher pressure?

Which alveolus is more likely to collapse?

A
34
Q

What is Laplace’s law?

A

It tells us that pressure in a spherical compartment is:

(1) proportional to the Tension and,
(2) inversely proportional to the radius of that sphere

35
Q

What are the effects of surfactant on an alveolus?

A

Surfactant causes surface tension (which contributes to alveolar wall tension, along with elastic recoil), to be lower in smaller spheres

36
Q

Which patients have surfactant deficiency and what does this cause?

A

Premature babies (< 30 weeks) have surfactant deficiency and are at risk for infant/neonatal respiratory distress syndrome from “alveolar collapse” due to high surface tension

37
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
38
Q

What 2 forces need to be overcome to inflate the lungs?

A

Force of elastic recoil

Force of airway resistance

39
Q

What is airway resistance?

A

Is the pressure difference between the alveoli and mouth, divided by the flow rate

40
Q

What is the equation for airway resistance?

A

Resistance = Pressure1-Pressure2 / Flow

(V=IR) (analogous to ohms law)

41
Q

Where does airway resistance originate from?

A

Airway resistance originates from friction between air and mucosa

42
Q

What is pulmonary resistance?

A

Pulmonary resistance = tissue + airway

Tissue forces are lung and chest wall sliding over each other (~ 20% of total)

43
Q

Is there an increase or decrease in cross sectional area in small airways?

A

Massive increase in cross section in small airways ‘trumpet’

44
Q

What is laminar flow and how is resistance generated?

A

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

45
Q

What is turbulent flow and how is resistance generated?

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

46
Q

Label the types of flow

A
47
Q

What is the Reynold’s number?

A

The “Reynold’s number” helps predicts when laminar flow converts to turbulent flow

48
Q

What is this?

Re = 2 (length) (density of gas) (velocity of gas)

viscosity of gas

A

The “Reynold’s number” helps predicts when laminar flow converts to turbulent flow

49
Q

How is resistance worked out?

A

-Resistance is described by the law equating resistance and radius

(Hagen-Poiseuille equation): R = (8 n l) / (P r4)

  • Resistance is inversely proportional to 4th power of radius
  • Flow is inversely proportional to the viscosity of a fluid
50
Q

Draw a graph showing airway resistance through different levels of the respiratory tree

A
51
Q

How is a generations (level of respiratory tree) resistance worked out?

A

All airways in a generation contribute to that generation’s total resistance (Rt)

52
Q

What are the factors affecting airway resistance?

A
  • Inflammation
  • Mucus
  • Bronchodilators
  • Steroids
  • Gas density
  • Heliox (lower Re)
  • Diving
53
Q

What is 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.

54
Q

How does elastic work lead to greater work of breathing?

A
  • Decreased elasticity in restrictive diseases
  • Greater wOB
55
Q

How does non-elastic lead to greater work of breathing?

A

Obstructive diseases lead to greater WOB to overcome increased airway resistance

56
Q

What does failure of work of breathing lead to?

A

Ventilatory support

103 Theme 4 - Lungs (21 decks)

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