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
What causes hysteresis?
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
26
Describe the action of surfactant during lung expansion
1. Increased area allows surfactant to spread over surface 2. Creates room for micelles to move to surface 3. Allows addition of more surfactant
27
What is the effect of infants w/ RDS lacking surfactant?
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)
28
What effects does reduction of surface tension by surfactant have?
* 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)
29
Describe the total compliance near FRC compared to individual compliances in lung and chest wall
Total compliance \< individual compliances (at FRC compliances of lung and chest wall are the same, like adding resistances in parallel)
30
Consider an isolated chest wall (no lungs) w/o any external forces acting on it. Making the chest wall stiffer will \_\_\_\_\_\_\_\_
Have no effect on its volume
31
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 \_\_\_\_\_\_\_\_
Have no effect on its volume
32
Lung and chest wall compliance determine \_\_\_\_\_
Lung and chest wall compliance determine FRC
33
What occurs in a pneumothorax?
* Lungs collapse due to elastic recoil of lungs * Chest wall expands
34
Say you stretch the lungs and attach them to the chest wall via a fluid layer. What occurs?
Lungs recoil, which pulls lungs and chest wall to a smaller volume (FRC) and produces a negative Pip
35
When the lungs recoil to a smaller volume, what occurs?
* Force of lung recoil decreases * Force of chest wall increases * FRC occurs when recoil force of lung = chest wall * Pip = -5 cm H2O
36
What is the effect of a low compliance (stiff) chest wall?
Low compliance (stiff) chest wall makes * FRC larger than w/ normal chest wall * Pip more negative
37
If the chest wall is stiffer (less compliant) than normal but the lungs are normal, FRC will be \_\_\_\_\_\_\_\_
If the chest wall is stiffer (less compliant) than normal but the lungs are normal, FRC will be larger than normal
38
What is the effect of a low compliance (stiff) lung?
Low compliance (stiff) lung * Decreases FRC (pulls chest to smaller volume) * Makes Pip more negative
39
If the lung is more compliant (emphysema) than normal but the chest wall is normal, FRC will be \_\_\_\_\_\_
If the lung is more compliant (emphysema) than normal but the chest wall is normal, FRC will be larger than normal
40
If the lung is more compliant (emphysema) than normal, at FRC the Pip will be \_\_\_\_\_\_\_
If the lung is more compliant (emphysema) than normal, at FRC the Pip​ will be less negative
41
Expanding lungs w/ low compliance requires ______ force
Expanding lungs w/ low compliance requires greater force
42
As you go down the lung, relative ventilation ________ and blood flow \_\_\_\_\_\_\_
As you go down the lung, relative ventilation increases and blood flow increases
43
44
Why is there a mismatch of ventilation and blood flow?
Ventilation increases from apex to base b/c gravity but blood flow increases from apex to base by a greater amount
45
At the apex, alveoli are _______ and \_\_\_\_\_\_\_, so there is _______ ventilation
At the apex, alveoli are larger and less compliant, so there is less ventilation
46
At the apex, there is ______ resistance, so there is ______ blood flow
At the apex, there is higher resistance, so there is less blood flow
47
At the base, alveoli are _______ and \_\_\_\_\_\_\_, so there is _______ ventilation
At the base, alveoli are smaller and more compliant, so there is more ventilation
48
At the base, there is ______ resistance, so there is ______ blood flow
At the base, there is lower resistance, so there is greater blood flow
49
Alveoli at ____ are pulled open
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
At residual volume, apex is ______ ventilated than the base
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
What occurs in congenital lobar emphysema?
* 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
During inspiration, an increase in airway resistance above the level of the glottis (e.g. inflamed tonsils and adenoids will make Pip \_\_\_\_\_\_\_
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
During expiration, inflammation of the tonsils and adenoids will make Pip \_\_\_\_\_\_\_
During expiration, inflammation of the tonsils and adenoids will make Pip less negative or more positive
54
What is the relationship between flow, PA, and airway resistance?
Flow = (PB - PA) / resistanceairway Flow is equal to pressure gradient divided by resistance of airway
55
Lung expansion during inspiration _______ PA
Lung expansion during inspiration decreases PA PA is closely related to airway resistance and airflow
56
For a given rate of lung expansion, the greater the resistance, the more PA will \_\_\_\_\_\_\_
For a given rate of lung expansion, the greater the resistance, the more PA​ will decrease
57
Decreasing PA makes the lung more _______ and makes Pip more \_\_\_\_\_\_\_
Decreasing PA makes the lung more difficult to expand (stiffer) and makes Pip more negative
58
Intrapleural pressure changes during a breath depend on _______ and \_\_\_\_\_\_\_
Intrapleural pressure changes during a breath depend on elastance and airway resistance
59
Effort independence occurs during ______ but not \_\_\_\_\_\_
Effort independence occurs during expiration but not inspiration
60
Peak expiratory flow occurs near \_\_\_\_\_
Peak expiratory flow occurs near TLC
61
In the Starling resistor, what occurs when Pe \> Pi \> PO ?
When Pe \> Pi \> PO​, tube collapses and flow = 0
62
In the Starling resistor, what occurs when Pi \> Po \> Pe ?
When Pi \> Po \> Pe, flow is a function of Pi - Po (∆P) (pressure in tube greater than pressure in airway)
63
In the Starling resistor, what occurs when Pi \> Pe \> Po ?
When Pi \> Pe \> Po, the tube will flutter open and closed and flow will be continuous and a function of Pi - Pe
64
Describe mechanical interdependence
Tethering reduces airway (and alveolar) collapse
65
What causes flow limitation?
Dynamic compression of the airways
66
On forced expiration, lateral pressure is lower where velocity is \_\_\_\_\_\_
On forced expiration, lateral pressure is lower where velocity is higher
67
Airway compression (when Pairway \< Pip) causes \_\_\_\_\_\_
Airway compression (when Pairway \< Pip) causes flow limitation
68
Describe dynamic airway compression
* Pip \> Pairway * Airways effectively tethered to chest wall * At larger lung volumes, tethers are stretched and more effectively stiffen airways
69
Describe effort independence
* Occurs during expiration but not inspiration * Influenced by tethering, so volume dependent * Emphsema increases lung compliance, decreasing tethering
70
Dynamic compression is effort \_\_\_\_\_\_\_\_
Dynamic compression is effort independent (flow limited) * As effort increases, Pip increases, increasing compression and limiting flow
71
What produces wheezing sounds?
Turbulent flow through narrowed airway produces wheezing sounds