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Pulm > SM_152a-154a: Mechanics II-IV > Flashcards

SM_152a-154a: Mechanics II-IV Flashcards

1
Q

Describe the pressure relationship in inspiration

A

PA < PB and PA < 0

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2
Q

Describe the pressure relationship in expiration

A

PA > PB

PA > 0

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3
Q

What creates the intrapleural pressure?

A

Lungs held against chest wall by thin layer of pleural fluid

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4
Q

Intrapleural pressure Pip is ______ than atmospheric pressure

A

Intrapleural pressure Pip is less than atmospheric pressure

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5
Q

What happens when there is a hole in the chest wall?

A

Pneumothorax

  • Pip = PB = 0
  • Lungs collapse
  • Cheast wall expands
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6
Q

What are the three transmural pressures?

A
  • Transpulmonary: Ptp = PA - Pip
  • Transthoracic: Ptt = Pip - PB
  • Transrespiratory: Ptr = PA - PB
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7
Q

How does one measure Pip?

A

With an esophageal ballon

Esophageal ballon pressure is a reasonable surrogate for Pip

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8
Q

What factors produce elastic recoil of the lung?

A
  • Tissue elastance
  • Surface tension
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9
Q

What causes tissue elastance?

What fibers are involved?

A

Stretching of the lung parenchyma

Fibers involved are

  • Elastin
  • Collagen (type IV) gives strength to alveolar basement membrame (geometry contributes to recoil)
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10
Q

What lung structure is involved in creation of surface tension?

A

Alveoli

(curved surfaces, lined w/ thin layer of fluid)

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11
Q

Surfactant _______ but does not _______ surface tension

A

Surfactant reduces but does not abolish surface tension

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12
Q

What is LaPlace’s Law for a soap bubble?

A

P = 4T / R

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13
Q

You have a small soap bubble and a large soap bubble connected by a stopcock. If the stopcock is turned so that the small and large bubbles are connected, what will happen?

A

The small bubble will empty into the large bubble

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14
Q

According to LaPlace’s Law, P increases as R ________.

Why?

A

According to LaPlace’s Law, P increases as R decreases

This occurs b/c surface tension is constant and b/c of geometry (alveoli have curved surfaces)

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15
Q

Why does surface tension contribute to recoil force of the lung? Use a beaker of water as a model.

A

The surface layer is compressed b/c unequal forces cause the surface layer to move closer to the one below it

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16
Q

How does surface tension produce pressure development in a bubble?

A

Attractive forces can be separates into horizontal and vertical components

The vertical components sum and point towards the center, which generates pressure

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17
Q

Describe the effect of bubble size on pressure

A

A larger radius bubble produces less inward pressure

(the vertical components are smaller because the radius is larrger)

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18
Q

Describe the influence of surfactant on surface tension in small versus large alveoli

A

There is a higher concentratiion of surfactant in small alveoli

  • Reduces surface tension more in small alveoli
  • Reduces tendency for small alveoli to collapse

Surfactant stabilizes small alveoli more

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19
Q

What occurs when there is a lack of surfactant?

A
  • Produces strong lung rectractile force (reduces compliance of lung)
  • Tends to collapse alveoli (millions of tiny curved surfaces, causes atelectasis in premature infants)
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20
Q

What is the formula for compliance?

A

Compliance = ∆V / ∆P

Greater slope means greater compliance (greater volume for a given change in pressure)

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21
Q

What factors contribute to lung compliance?

A
  • Elastic components of lung tissue (elastin)
  • Geometry (mesh) of collagen fibers
  • Surface tension
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22
Q

What is the effect of filling a lung with saline?

A
  • Abolished surface tension (removes air-fluid interface)
  • Increases compliance (steeper slope)
  • Markedly reduces hysteresis (surfactant produces hysteresis)
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23
Q

What is hysteresis?

A

Different pressure for a given lung volume during inflation compared to exhalation

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24
Q

What is surfactant composed of?

What cells produce surfactant?

A

30% protein + 70% phospholipid (dipalmitoyl phosphatidyl choline)

Produced by type II alveolar epithelial cells (activated at 30 weeks gestation)

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25
Q

What causes hysteresis?

A

Addition of surfactant to fluid surface (from micelles) during lung expansion increases the surfactant concentration, which is higher at any specified lung volume during deflation versus inflation

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26
Q

Describe the action of surfactant during lung expansion

A
  1. Increased area allows surfactant to spread over surface
  2. Creates room for micelles to move to surface
  3. Allows addition of more surfactant
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27
Q

What is the effect of infants w/ RDS lacking surfactant?

A

Lungs tend to collapse after each breath, so every breath requires a large effort

(normally, surfactant is distributed over the first few breaths, so the effort required for each breath reaches a steady state value which is much lower than for the first breath)

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28
Q

What effects does reduction of surface tension by surfactant have?

A
  • Reduces work of breathing (increases lung compliance)
  • Helps stabilize alveoli (reduces tendency for small alveoli to collapse)
  • Causes surface tension to vary w/ surface area (i.e. hysteresis)
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29
Q

Describe the total compliance near FRC compared to individual compliances in lung and chest wall

A

Total compliance < individual compliances

(at FRC compliances of lung and chest wall are the same, like adding resistances in parallel)

30
Q

Consider an isolated chest wall (no lungs) w/o any external forces acting on it. Making the chest wall stiffer will ________

A

Have no effect on its volume

31
Q

Consider an isolated lung (outside the thorax) w/o any external forces acting on it. Making this lung stiffer (e.g. idiopathic pulmonary fibrosis) will ________

A

Have no effect on its volume

32
Q

Lung and chest wall compliance determine _____

A

Lung and chest wall compliance determine FRC

33
Q

What occurs in a pneumothorax?

A
  • Lungs collapse due to elastic recoil of lungs
  • Chest wall expands
34
Q

Say you stretch the lungs and attach them to the chest wall via a fluid layer. What occurs?

A

Lungs recoil, which pulls lungs and chest wall to a smaller volume (FRC) and produces a negative Pip

35
Q

When the lungs recoil to a smaller volume, what occurs?

A
  • Force of lung recoil decreases
  • Force of chest wall increases
  • FRC occurs when recoil force of lung = chest wall
  • Pip = -5 cm H2O
36
Q

What is the effect of a low compliance (stiff) chest wall?

A

Low compliance (stiff) chest wall makes

  • FRC larger than w/ normal chest wall
  • Pip more negative
37
Q

If the chest wall is stiffer (less compliant) than normal but the lungs are normal, FRC will be ________

A

If the chest wall is stiffer (less compliant) than normal but the lungs are normal, FRC will be larger than normal

38
Q

What is the effect of a low compliance (stiff) lung?

A

Low compliance (stiff) lung

  • Decreases FRC (pulls chest to smaller volume)
  • Makes Pip more negative
39
Q

If the lung is more compliant (emphysema) than normal but the chest wall is normal, FRC will be ______

A

If the lung is more compliant (emphysema) than normal but the chest wall is normal, FRC will be larger than normal

40
Q

If the lung is more compliant (emphysema) than normal, at FRC the Pip will be _______

A

If the lung is more compliant (emphysema) than normal, at FRC the Pip​ will be less negative

41
Q

Expanding lungs w/ low compliance requires ______ force

A

Expanding lungs w/ low compliance requires greater force

42
Q

As you go down the lung, relative ventilation ________ and blood flow _______

A

As you go down the lung, relative ventilation increases and blood flow increases

43
Q
A
44
Q

Why is there a mismatch of ventilation and blood flow?

A

Ventilation increases from apex to base b/c gravity but blood flow increases from apex to base by a greater amount

45
Q

At the apex, alveoli are _______ and _______, so there is _______ ventilation

A

At the apex, alveoli are larger and less compliant, so there is less ventilation

46
Q

At the apex, there is ______ resistance, so there is ______ blood flow

A

At the apex, there is higher resistance, so there is less blood flow

47
Q

At the base, alveoli are _______ and _______, so there is _______ ventilation

A

At the base, alveoli are smaller and more compliant, so there is more ventilation

48
Q

At the base, there is ______ resistance, so there is ______ blood flow

A

At the base, there is lower resistance, so there is greater blood flow

49
Q

Alveoli at ____ are pulled open

A

Alveoli at apex are pulled open

(local compliance is higher for alveoli in base, ∆P is same at top and base of lung while ∆V is larger at base)

50
Q

At residual volume, apex is ______ ventilated than the base

A

At residual volume, apex is better ventilated than the base

(Pip is positive at the base: small airways are collapsed, compliance is smaller in the base than the apex)

51
Q

What occurs in congenital lobar emphysema?

A
  • Overinflation of one or pulmonary lobes
  • High compliance of diseased lobes, so diseases lobes expand more readily than healthy lobes, which reduces expansion of healthy lung region
52
Q

During inspiration, an increase in airway resistance above the level of the glottis (e.g. inflamed tonsils and adenoids will make Pip _______

A

During inspiration, an increase in airway resistance above the level of the glottis (e.g. inflamed tonsils and adenoids will make Pip more negative

53
Q

During expiration, inflammation of the tonsils and adenoids will make Pip _______

A

During expiration, inflammation of the tonsils and adenoids will make Pip less negative or more positive

54
Q

What is the relationship between flow, PA, and airway resistance?

A

Flow = (PB - PA) / resistanceairway

Flow is equal to pressure gradient divided by resistance of airway

55
Q

Lung expansion during inspiration _______ PA

A

Lung expansion during inspiration decreases PA

PA is closely related to airway resistance and airflow

56
Q

For a given rate of lung expansion, the greater the resistance, the more PA will _______

A

For a given rate of lung expansion, the greater the resistance, the more PA​ will decrease

57
Q

Decreasing PA makes the lung more _______ and makes Pip more _______

A

Decreasing PA makes the lung more difficult to expand (stiffer) and makes Pip more negative

58
Q

Intrapleural pressure changes during a breath depend on _______ and _______

A

Intrapleural pressure changes during a breath depend on elastance and airway resistance

59
Q

Effort independence occurs during ______ but not ______

A

Effort independence occurs during expiration but not inspiration

60
Q

Peak expiratory flow occurs near _____

A

Peak expiratory flow occurs near TLC

61
Q

In the Starling resistor, what occurs when Pe > Pi > PO ?

A

When Pe > Pi > PO​, tube collapses and flow = 0

62
Q

In the Starling resistor, what occurs when Pi > Po > Pe ?

A

When Pi > Po > Pe, flow is a function of Pi - Po (∆P)

(pressure in tube greater than pressure in airway)

63
Q

In the Starling resistor, what occurs when Pi > Pe > Po ?

A

When Pi > Pe > Po, the tube will flutter open and closed and flow will be continuous and a function of Pi - Pe

64
Q

Describe mechanical interdependence

A

Tethering reduces airway (and alveolar) collapse

65
Q

What causes flow limitation?

A

Dynamic compression of the airways

66
Q

On forced expiration, lateral pressure is lower where velocity is ______

A

On forced expiration, lateral pressure is lower where velocity is higher

67
Q

Airway compression (when Pairway < Pip) causes ______

A

Airway compression (when Pairway < Pip) causes flow limitation

68
Q

Describe dynamic airway compression

A
  • Pip > Pairway
  • Airways effectively tethered to chest wall
  • At larger lung volumes, tethers are stretched and more effectively stiffen airways
69
Q

Describe effort independence

A
  • Occurs during expiration but not inspiration
  • Influenced by tethering, so volume dependent
  • Emphsema increases lung compliance, decreasing tethering
70
Q

Dynamic compression is effort ________

A

Dynamic compression is effort independent (flow limited)

  • As effort increases, Pip increases, increasing compression and limiting flow
71
Q

What produces wheezing sounds?

A

Turbulent flow through narrowed airway produces wheezing sounds

Pulm (32 decks)

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