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Resp Physiology > Lung Mechanics > Flashcards

Lung Mechanics Flashcards

1
Q

What is the work of breathing deterimined by

A

lungs

Thoracic compliance

Airway resistance

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2
Q

What is compliance

A

Ease with which lungs can be expanded

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3
Q

What is embedded in elastic tissue

A

Lungs

Airway tree

Vascular tree

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4
Q

What is trans-pulmonary pressure

A

P difference between alveoli and pulmonary wall

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5
Q

If lungs are easy to inflate, what sort of compliance do they have

A

Increased compliance

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6
Q

Formula for compliance

A

Change in vol/change in P

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7
Q

Transpulmonary pressure difference from apex to base

A

APEX = -10

MIDDLE = -5

BASE = -2.5

-ve P is the suction that keeps the lungs open

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8
Q
  1. Where is there greater alveolar volume
  2. Where is there greater alveolar ventilation
A
  1. Apex
  2. Base
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9
Q

Which part of the lung is most compliant

A

Base of lung

Smaller alveoli at base => easier to expand alveoli at base

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10
Q

What does lung compliance depend on

A
  1. Distensibility - easy to stretch/deflate - ELASTIN
  2. Elasticity - w/o it, lungs would enlarge with every breath and compliance would be 0 - COLLAGEN
  3. Surface tension
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11
Q

Consequence of decreased compliance

A

Increased stiffness, increased work to inflate lungs

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12
Q

Background of pneumonia

A

Fluid in lung tissue, alters surface tension of alveoli, changes surfactant and makes it more difficult to control lungs

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13
Q

conditions affected by compliance

A

Fibrosis

COPD

Emphysema

Chronic bronchitis

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14
Q

Factors that influence compliance

A
  • Posture
  • Age
  • Post-laproscopic surgery
  • Occasional deep breaths
  • Pregnancy
  • High standing diaphragm - obesity, scoliosis
  • Lung disease
  • Pneumothorax - trauma, diving, underlying lung pathologies

DECREASED COMPLIANCE WHEN:

Lung is unventilated for long period, increased surface tension within alveoli, lungs engorged with blood (increase pulmonary venous pressure)

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15
Q

High or low compliance with EMPHYSEMA

A

HIGH CL

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16
Q

High or low compliance with FIBROSIS

A

Low CL

17
Q

2 determinants of lung compliance

A

R due to elasticity of lung (25%)

  • Elastic fibres in interstitium of alveolar walls
  • Thick alveolar wall => increased elastic fibres => increased R to stretch

Surface tension @ air-water interface in alveoli (75%)

  • Alveolar spaces lined with a thin layer of water
  • Attractive forces between water molecules (= ST) counteracts expansion of water lining
  • Energy is required to overcome ST of this water layer in order to expand
18
Q

When is surfactant produced and how

What is its composition

A

Produced by type II alveolar cells from week 28 gestation

90% lipids, 10% proteins => AMPHIPHATIC

19
Q

Infant respiratory distress syndrome

A

Decreased CL

Atelectasis

Oedema

Exogenous surfactant

20
Q

#AD

Name the 2 large hydrophilic surfactant proteins

A
  1. SP A
  2. SP D
21
Q

Name the 2 small hydrophobic surfactant proteins

A
  1. SP B
  2. SP C
22
Q

Name the 7 lipids in surfactant

A
  1. Dipalmitoylphosphatidylcholine (DPPC - 60%)
  2. Phosphatidylglycerol
  3. Phosphatidic acid
  4. Phosphatidylinositol
  5. Phosphatidylethanolamine
  6. Phosphatidylcholine
  7. Cholesterol - most abundant neutral lipid present
23
Q
  1. How much surface tension does DPPC produce
  2. What does it form
A
  1. Generates near 0 surface tension at interface during compression
  2. Forms tightly packed monolayer which can generate these low ST values w/o collapsing

intermolecular repulsive forces oppose attractive forces between liquid surface H2O molecules

EFFECT IS STRONGER AT LOWER ALVEOLAR VOLUMES

24
Q

Deficiency of SP A

A

More susceptible to pathogens

25
Q

SP B

A

Decreases surface tension

SP B deficiency in humans leads to RDS (resp distress syndrome)

Stabilises lipid monolayers

anti-bacterial

26
Q

SP C

A

found only in lungs

Linked to SP B

27
Q

Physiological roles of surfactant proteins

A
  1. Decrease ST to increase compliance - decreased work of expanding lungs at each breath
  2. Increased stability of alveoli - decrease small alveoli emptying into larger ones
  3. Helps to keep alveoli dry because ST of alveolus liquid layer would draw water into alveolus
28
Q

Law of Laplace

A

P = 2T/r

P is greater in smaller alveolus

29
Q

Hysteresis

A

V/P relationship is different during expiration

30
Q

What is vol at any pressure greater for

A

Greater for deflation than inflation

31
Q

What does most of hysteresis and CL appear due to

A

Surface tension of alveoli

32
Q

How does surface tension affect alveoli

A

Inflation of lungs with saline eliminates air-liquid interface and surface tension

Musch easier to inflate lungs with saline

  • elastic recoil is diminished due to lack of ST
  • not much difference between inflation and deflation => no HYSTERESIS
33
Q

3 reasons for hysteresis

A
  1. Changes in surfactant activity - ST greater in inspiration
  2. Stress relaxation - inherent property of elastic tissue - crinkled structure of collagen in lungs
  3. Re-distribution of gas - fast and slow alveoli
34
Q

Relationship between lung and chest wall

A

Lung and chest wall in series with each other - total compliance

35
Q
  1. Lung compliance
  2. Chest wall compliance
  3. Total compliance
A
  1. Change in lung vol/change in Ptp
  2. Change in lung vol/change in trans-chest wall P
  3. 100 ml/cmH2O

Resp Physiology (9 decks)

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