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Physiology- CP > Pulmonary Function Tests > Flashcards

Pulmonary Function Tests Flashcards

1
Q

What is the tidal volume?

A
  • Normal breathing in and out
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2
Q

What is the inspiratory reserve volume?

A
  • After breathing normally, further breathing until the lungs are full
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3
Q

What is the expiratory reserve?

A
  • After breathing out normally, blow all air out of lungs
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4
Q

What is the residual volume?

A
  • Volume of air that resides in the lungs but cannot be blown out
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5
Q

What is air flow driven by mechanically?

A

Pressure changes

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6
Q

Describe how pressure changes in the lungs work

A
  • Requires a pressure gradient
  • Air flow moved from high pressure to low and so air is sucked into the lungs
  • Relative to atmospheric pressure
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7
Q

What does negative intrapulmonary pressure lead to?

A

Inspiration

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8
Q

What does positive intrapulmonary pressure lead to?

A

Expiration

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9
Q

Describe the mechanics of inspiration

A
  • Air flow in
  • Due to contraction and contraction (flattening) of the diaphragm and external intercostal muscles
  • Created negative pressure and draws air in
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10
Q

Describe the mechanics of expiration

A

Air flows out

  • Largely passive due to elastic recoil that drives air out (up until the functional residual capacity is reached)
  • Beyond FRC expiratory muscles need to contract
  • Also, to achieve higher pressures and therefore flows
  • A higher pressure generated by squeezing thorax
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11
Q

What is the alveolar pressure the sum of?

A
  • Pleural pressure determined by muscular effort

- Elastic recoil generated by the elastic properties (and surface tension)

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12
Q

What increases the elastic recoil pressure?

A

Volume

- Collapse alveoli and increase alveolar pressure

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13
Q

Therefore how does alveolar pressure become greater than atmospheric?

A
  • Increasing either pleural pressure or elastic pressure
  • But only up to a point
  • Expiratory effort is limited
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14
Q

In what circumstance does increase in pressure not necessarily increase flow?

A

Flow envelope

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15
Q

What limits peak expiratory flow?

A

Volume

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16
Q

What determines air flow?

A
  • Resistance
  • Affected by diameter of small airways
  • Resistance increases with effort as small airways are compressed by raised external pressure
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17
Q

Is there interdependence between alveoli?

A

Yess

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18
Q

How do large volumes affect peak flow?

A
  • increase since elastic recoil increases with volume
  • While resistance decreases due to radial traction
  • As you breathe in, everything stretches
  • Always are wide and have lower resistance
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19
Q

What does maximal output require?

A
  • Maximal drops in resistance

- Harder when you breathe out, more pressure is applied across airways

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20
Q

What is the benefit of airways with cartilage?

A
  • Will not collapse
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21
Q

Which airways would collapse when pressure increases and when?

A
  • Lower airways with no cartilage

- Only occurs in forced expiration

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22
Q

What opposes airway collapse in lower airways?

A
  • Radial traction from interdependence
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23
Q

What does puffing fo on expiration (pursing lips)?

A
  • Critical closing point can be moved into area of airway held open by cartilage
  • Often done by patients with emphysema that lack interdependence
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24
Q

What is Ohm’s Law?

A

Voltage = Current x Resistance

25
Q

How does Ohm’s Law apply to movement of air?

A
  • Voltage- pressure difference
  • Current- perfusion/flow (Q)
  • Resistance (R)
  • Pressure difference- QR
26
Q

What increases resistance?

A

Force of breathing

27
Q

What is lung compliance?

A
  • How hard it is to stretch the lung and chest wall
  • Decrease compliance in pulmonary fibrosis and CVD, e.g. heart failure
  • Restrictive lung disease
  • Fibrotic lungs are stiff and hard, therefore not very compliant
28
Q

What is lung resistance?

A
  • Resistance to movement of air through the airway
  • Increased in asthma and COPD (obstructive lung disease)
  • Airflow becomes problematic
  • Investigated through spirometry
29
Q

What is spirometry?

A
  • Measurement of pattern of air movement into and out of lungs
  • During controlled ventilatory manoeuvres
  • Often does as a maximal expiratory manoeuvre
30
Q

What can spirometry measure?

A
  • Both resistance and compliance

- Will record FEV1 and FVC

31
Q

What are spirometry results dependent on?

A
  • Results dependent on mechanical ability of lung and factors which alter resistance
  • Which can also be mechanical
32
Q

What is the forced vital capacity?

A
  • Total volume of air that can be exhaled forcefully from full inflation (TLC) measured in litres
33
Q

How long does it normally take for the majority of FVC to be exhaled?

A
  • less than 3 seconds

- Often prolonged in obstructive diseases

34
Q

What is FEV1?

A
  • Volume that can be forcefully expired from full inflation (TLC) in the first second
  • Measured in litres
  • Resistance
35
Q

What is the normal FEV1?

A
  • 70-80% of FVC in the first second
  • Athletes and physically may achieve more
  • Those with respiratory disease may do less
36
Q

What is the classification of severity of FEV1 interpretation?

A
  • > 75%- Normal
  • 60-75%- mild obstruction
  • 50-59%- moderate obstruction
  • <49% severe obstruction
37
Q

What is the classification of severity of FVC interpretation?

A
  • 80-120%- Normal
  • 70-79%- mild reduction
  • 50-69%- moderate reduction
  • <49% severe reduction
38
Q

Why is full inflation important?

A
  • Maximal can allow for a reproductive test
  • Also leads to the least possible resistance
  • Best possible flow
39
Q

What are the patterns in spirometry that reflect obstruction?

A
  • Long flow

- All air will come out due to higher resistance

40
Q

What are the patterns in spirometry that reflect restriction?

A
  • FEV1 drops in proportion to normal
  • Smaller amount of air exhaled
  • Appropriate percentage FVC1 is removed
41
Q

What are obstructive disorders characterised by?

A
  • Low expiratory flow

- Typically due to increased resistance

42
Q

How does obstructive disorders present?

A
  • Low FEV1 with normal FVC
  • FVC may be lower but nor substantially
  • Crucially, FEV1 will be less than 80% of the FVC
  • E.g. asthma and COPD
43
Q

Describe asthma

A
  • Characterised by bronchoconstriction- increased airway resistance
  • Increased resistance impairs expiratory flow leading to obstruction
  • Expiratory flows are more greatly affected since resistance to inspiration is less
  • Excess mucous is also present in these smaller airways which leads to increased obstruction
44
Q

Describe chronic obstructive pulmonary disorder (COPD) (bronchitis)

A
  • excessive mucous production in airway
  • leads to mucous plugging, inflammatory cell infiltration and oedema
  • All of which can impede airflow, leading obstruction
45
Q

Describe chronic obstructive pulmonary disorder (COPD) (emphysema)

A
  • Excessive protease activity
  • Loss of elastic recoil removes large drive of expiration- makes forced expiration more important
  • Loss of radial traction increases airway collapse and air trapping
  • Presents as obstruction
46
Q

What are restrictive conditions characterised by?

A
  • Diminished lung volume

- Typically this is due to decreased compliance and so decreasing inspiration

47
Q

Why is compliance decreased in restrictive conditions?

A
  • Changes in lung parenchyma (interstitial lung disease)
  • Diseases of pleura, chest wall (e.g. scoliolosis), or neuromuscular apparatus (e.g. muscular dystrophy)
  • Seen as decreased FVC but normal FEV1/FVC ratio
48
Q

Describe pulmonary fibrosis

A
  • A number of conditions lead to pulmonary fibrosis
  • Here, parenchyma is replaced by fibrous tissue
  • Leads to stiffer, less compliant lungs that are harder to inflate and have less elastic recoil
49
Q

Give examples of conditions that lead to pulmonary fibrosis

A
  • Interstitial lung disease, asbestosis, idiopathic pulmonary fibrosis, farmer’s lungs and pigeon fancier’s lung
50
Q

What is heart failure?

A
  • Failure to eject sufficient blood from the left ventricle

- Also fails to clear it from lungs

51
Q

What happens to the lungs during heart failure?

A
  • Lungs become engorged with blood as it becomes congested
  • Lungs become stiffer and harder to inflate
  • Increased resistance- obstruction
  • Decreased compliance- restriction
52
Q

What do flow volumes loops provide?

A
  • Graphical illustration of a patients spirometric
53
Q

Describe flow volume loops

A
  • Flow (y-axis) is plotted against volume (x-axis) to display a continuous loop from inspiration to expiration
  • Overall shape of flow volume loop is important in interpreting spirometric results
54
Q

Why would having a non-maximal inspiration result in invalid results?

A
  • Maximal inspiration was vital to get best flow

- Here flows will appear reduced and may present, wrongly, as restrictive

55
Q

Why could coughs result in invalid results?

A
  • Can give a false indication of both FEV1 and FVC

- Any variable including a cough should be ignored

56
Q

Why would sub-maximal result in invalid results?

A
  • By definition obstruction is a reduced expiration

- As such poor technique appears obstructive

57
Q

Why would early termination result in invalid results?

A
  • Most adults breathe out for more than 6 seconds
  • In obstruction it takes longer to reach plateau
  • Ending early gives a false, lower FVC and might suggest restriction
  • Equally, it might inflate the FEV1/FVC ratio and hide an obstructive disorder
58
Q

Why would a partially obstructive mouthpiece result in invalid results?

A
  • May cause obstruction and falsely report an obstructive disorder
  • May also (depending on obstruction) lead to air loss reducing FVC, an so, giving a false restrictive
59
Q

Why would a leak result in invalid results?

A
  • Whether in the tubing or by subject failing to seal
  • Similar to early termination
  • Since air is not being recorded the FVC will be taken as low
  • Lower FVC suggests restriction
  • Equally, it might inflate FEV1/FVC ration to hide an obstructive disorder

Physiology- CP (19 decks)

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