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Respiratory > Physiology and function in restrictive lung disorders > Flashcards

Physiology and function in restrictive lung disorders Flashcards

1
Q

What is a restrictive disorder?

A

A disorder in which prevents normal expansion of the lungs

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2
Q

What can cause lung restriction?

A
  • Extra-pulmonary disease (visceral pleura, pleural space, chest wall including parietal pleura, bones, muscles, nerves)
  • Intra-pulmonary disease (alveolar spaces)
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3
Q

What are the 5 examples of extra-pulmonary restriction?

A
  • Integrity of nerves to respiratory muscles (high cervical dislocation)
  • Impaired neuromuscular junctions (myasthenia gravis)
  • Impaired muscles (muscular dystrophy)
  • Pleural thickening (asbestos exposure)
  • Skeletal abnormalities (scoliosis)
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4
Q

Examples of diseases causing increased fibrous tissue in the lungs (intra-pulmonary)

A
  • Silicosis in a stonemason
  • Asbestosis
  • Drug-induced lung fibrosis
  • Coal-workers pneumoconiosis
  • Rheumatoid-lung
  • Bird-fanciers lung
  • Idiopathic pulmonary fibrosis
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5
Q

How do fibrotic lung diseases cause restrictive disorders?

A
  • Inflation pressure
  • Pulmonary compliance (the ability of the lungs to stretch during a change in volume relative to an applied change in pressure= stretchability)
  • Elastic recoil pressure (=alveolar pressure minus pleural pressure)
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6
Q

What is the relationship between inflation pressure, compliance and elastic recoil?

A
  • A lower compliance means greater inflation pressure required to inflate which means higher elastic recoil
  • Elastic recoil not the same as elastance
  • Elastance is the reciprocal of compliance hence= change in pressure/ change in volume
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7
Q

What is the effect of decreased compliance on inflation?

A
  • Increased fibrous tissue (more rigid)
  • Decreased compliance (requires high pressure to inflate)
  • Increased elastic recoil (deflates easily)
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8
Q

What is the effect of increased compliance on inflation?

A
  • Associated with an obstructive defect, particularly emphysema
  • Decreased elastic tissue (more floppy)
  • Increased compliance (inflates at low pressures)
  • Decreased elastic recoil (difficult to deflate)
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9
Q

How are lungs different to balloons?

A
  • Alveoli are moist

- Alveoli are of different sizes

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10
Q

How does moisture affect alveoli?

A

-Moisture causes surface tension which influences the pressure inside a sphere
-Inward force generated by fluid layer surface tension (sT)
-Laplace’s Law for a sphere:
P = (2 x sT)/ radius

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11
Q

How does size affect alveolar pressure?

A
  • Same inflation pressure and same surface tension
  • Well-inflated alveolus, large radius= relatively low alveolar pressure
  • Under-inflated alveolus, small radius= relatively high alveolar pressure
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12
Q

How does having different sized alveoli affect instability?

A
  • Air moves from high pressure area to low pressure area
  • Smaller alveolus empties into larger alveolus
  • There is instability of adjacent alveoli
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13
Q

What is surfactant?

A
  • Surface Active Agent
  • Produced by alveolar Type 2 cells
  • Composed of lipids (90%, mainly phospholipids) and proteins (10%)
  • Reduces surface tension
  • Hydrophobic end (fatty acids) in gas and hydrophilic end (glycerol, phosphate and choline) in liquid
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14
Q

What are the mechanisms of action of surfactant in well-expanded alveoli?

A
  • Surfactant spread evenly over alveolar surface but molecules spread out
  • Surfactant has little effect on surface tension
  • Large radius= high surface tension
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15
Q

What are the mechanisms of action of surfactant in deflated alveoli?

A
  • Tightly packed surfactant molecules
  • Some surfactant molecules extruded from the surface
  • Surfactant significantly reduces surface tension with accompanying lower pressure
  • Small radius= low surface tension
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16
Q

What is Respiratory Distress Syndrome of the New-born?

A
  • Surfactant deficiency
  • Surfactant first produced 210 days (30 weeks), c.f. full term= 280 days (40 days) so preterm birth
  • Low compliance
  • High inflation pressures
  • Rapid shallow breathing (fatigue)
  • Hypoxaemia
17
Q

What is primary surfactant deficiency?

A 
-Very rare in adult disease
Impaired surfactant biology contributes to pathogenesis of
-Adult respiratory distress syndrome
-pneumonia
-idiopathic pulmonary fibrosis
-lung transplant
18
Q

Describe the patterns of abnormal lung function of mild/moderate obstructive disease

A

FVC, TLC, VC all normal
FEV1, FEV1/FVC ratio decreased
RV, RV/TLC ratio increased

19
Q

Describe the patterns of abnormal lung function of severe obstructive disease

A

FVC, VC normal or small or decreased
FEV1, FEV1/FVC ratio decreased
TLC, RV, RV/TLC ratio increased

20
Q

Describe the patterns of abnormal lung function of restrictive disease

A

FEV1, FVC, TLC, VC decreased
RV normal or decreased
FEV1/FVC ratio, RV/TLC ratio normal or increased

21
Q

What are predicted values based on?

A

Age
Gender
Height
Ethnic origin

22
Q

What is the effect of age on FEV1?

A

0-18 increased in children

40+ decreases in adults

23
Q

What is the Gas Transfer Measurement?

A

Gas transfer is a measure of the diffusing capacity of the lung
Requires a measurement of gas exchange and alveolar volume

24
Q

What is the ideal gas for gas exchange?

A

-Rapidly taken up by haemoglobin with very high affinity
-Not produced by the body
-Non-toxic
-Easy to measure
Carbon monoxide

25
Q

What is the ideal gas for alveolar volume?

A

-Not taken up by haemoglobin
-Not produced by the body
-Non-toxic
-Easy to measure
Helium

26
Q

Describe the Carbon Monoxide Gas Transfer Measurement

A 
Single breath method
Inspired test gas contains 0.3% CO, 10% helium and air
Breathhold at TLC approx. 10 secs
Washout
Alveolar sample
27
Q

What does the CO Gas Transfer Measurement help to calculate?

A

TLCO (mmol/min/kPa) Total gas exchange capacity
Va Alveolar volume= number of contributing lung units
KCO Efficiency of gas transfer per unit of lung

28
Q

How does TLCO and KCO help differentiate between extra and intra pulmonary diseases?

A

Extra- TLCO low (lungs are smaller), KCO high (alveoli are normal and tightly packed with blood vessels)
Intra- TLCO low (lungs are smaller), KCO low (alveoli are abnormal)

Respiratory (41 decks)

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