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Systems: Respiratory AB > 4. Compliance and Lung Function Tests > Flashcards

4. Compliance and Lung Function Tests Flashcards

1
Q

What is surfactant?

A

Detergent like fluid produced by Type II alveolar cells

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2
Q

What does surfactant do?

A
  • Reduces surface tension on alveolar surface membrane thus reducing tendency for alveoli to collapse
  • Increases lung compliance
  • Reduces lung’s tendency to recoil
  • Makes work of breathing easier
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3
Q

Where does surface tension occur?

A

Where ever there is an air-water interface and refers to the attraction between water molecules

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4
Q

Why is surfactant more effective in small alveoli than large alveoli?

A

Surfactant molecules come closer together and are therefore more concentrated

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5
Q

When is surfactant produced?

A

Production starts at 25 weeks gestation and is complete by 36 weeks

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6
Q

What stimulates surfactant production?

A

Thyroid hormones and cortisol which increase towards the end of pregnancy

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7
Q

What can premature babies suffer from due to incomplete production of surfactant?

A

Infant Respiratory Distress Syndrome (IRDS)

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8
Q

Why is there less change in pressure in a saline filled lung compared to lung inflation in utero?

A

There is no need to overcome surface tension as there is not= air-water interface

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9
Q

Compliance

A

Change in volume relative to change in pressure

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10
Q

What does compliance represent?

A

The stretchability of the lungs

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11
Q

What does high compliance mean?

A

A large increase in lung volume for small decrease in ip pressure

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12
Q

What does low compliance mean?

A

Small increase in lung volume for large decrease in ip pressure

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13
Q

What can affect compliance?

A
  • Disease states

- Age

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14
Q

Why does expiration require effort in emphysema?

A

Loss of elastic tissue

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15
Q

Why does inspiration require effort in fibrosis?

A

Inert fibrous tissue

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16
Q

Why is expiration usually passive?

A

Normally effort (work) of inspiration is recovered as elastic recoil during expiration

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17
Q

Why does the pressure volume curve vary between apex and base of the lung?

A

At the base, the volume change is greater for a given change in pressure

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18
Q

Why does compliance decline with height from base to apex?

A
  • The alveoli at the apex are more inflated due to FRC.
  • At the base the alveoli are compressed between the weight of the lung above and the diaphragm below, hence more compliant on inspiration
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19
Q

How does alveolar ventilation vary between apex and base?

A

Declines with height from base to apex

20
Q

What does a small change in ip pressure result in?

A

A larger change in volume at the base compared to the apex

21
Q

Obstructive Lung Disease

A
  • Obstruction of air flow, especially on expiration

- Increased airway resistance

22
Q

Restrictive Lung Disease

A

Restriction of lung expansion

23
Q

What are 2 examples of obstructive lung disorders?

A
  • Asthma

- COPD

24
Q

Chronic bronchitis

A

Inflammation of the bronchi

25
Q

Emphysema

A

Destruction of the alveoli, loss of elasticity

26
Q

What is the prevalence of COPD?

A
  • 80 million people worldwide moderate to severe COPD

- Increases with age

27
Q

What are examples of restrictive lung disorders?

A
  • Fibrosis
  • Infant Respiratory Distress Syndrome
  • Oedema
  • Pneumothorax
28
Q

What is fibrosis?

A

Formation or development of excess fibrous connective tissue

29
Q

What are 2 causes of fibrosis?

A
  • Idiopathic

- Asbestosis

30
Q

What are restrictive lung diseases cause by?

A
  • Loss of lung compliance
  • Lung stiffness
  • Incomplete lung expansion
31
Q

Spirometry

A

Technique commonly used to measure lung function

32
Q

How can spirometry measurements be classed?

A

Static or dynamic

33
Q

Spirometry: Static

A

Where the only consideration made is the volume exhaled

34
Q

Spirometry: Dynamic

A

Where the time taken to exhale a certain volume is what is being measured

35
Q

What volumes can be measured directly by spirometry?

A

-Tidal volume
-Inspiratory reserve volume
-Expiratory reserve volume
Inspiratory capacity
Vital capacity

36
Q

What is the normal value for forced vital capacity?

A

5L

37
Q

What is the normal value for forced expiratory volume in 1 second?

A

4L

38
Q

What is the normal value for FEV1:FVC?

A

80%

39
Q

What is the value of FEV1:FVC for obstructive lung diseases?

A

42%

40
Q

What is the value of FEV1:FVC for restrictive lung disease?

A

90%

41
Q

Describe COPD

A
  • Rate at which air is exhaled is much slower
  • Total volume is also reduced
  • Major effect is on airways and so FEV is reduced to a greater extent than FVC
  • Ratio also reduced
42
Q

Describe pulmonary fibrosis.

A
  • Absolute rate of airflow is reduced
  • Total volume due to limitations to lung expansion
  • Ratio remains constant or can increase as a large proportion of volume can be exhaled in the first second
43
Q

What limitations exist of the FEV1/FVC ratio?

A
  • Obstructive, both FEV and FVC fall but FEV more so, so ratio is reduced
  • Restrictive, both FEV and FVC fall so ratio remains much the same despite severe compromise of function
  • Therefore normal FEV1/FVC ratio not always indicative of health
44
Q

What is the forced expiratory flow?

A

Average expired flow over the middle of an FVC

45
Q

How does FEV1 and FEF differ?

A
  • FEF correlates with FEV1 but changes are generally more striking
  • However, normal range is greater

Systems: Respiratory AB (39 decks)

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