Pulmonary Function Tests Flashcards
1
Q
What is the tidal volume?
A
- Normal breathing in and out
2
Q
What is the inspiratory reserve volume?
A
- After breathing normally, further breathing until the lungs are full
3
Q
What is the expiratory reserve?
A
- After breathing out normally, blow all air out of lungs
4
Q
What is the residual volume?
A
- Volume of air that resides in the lungs but cannot be blown out
5
Q
What is air flow driven by mechanically?
A
Pressure changes
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
7
Q
What does negative intrapulmonary pressure lead to?
A
Inspiration
8
Q
What does positive intrapulmonary pressure lead to?
A
Expiration
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
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
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)
12
Q
What increases the elastic recoil pressure?
A
Volume
- Collapse alveoli and increase alveolar pressure
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
14
Q
In what circumstance does increase in pressure not necessarily increase flow?
A
Flow envelope
15
Q
What limits peak expiratory flow?
A
Volume
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
17
Q
Is there interdependence between alveoli?
A
Yess
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
19
Q
What does maximal output require?
A
- Maximal drops in resistance
- Harder when you breathe out, more pressure is applied across airways
20
Q
What is the benefit of airways with cartilage?
A
- Will not collapse
21
Q
Which airways would collapse when pressure increases and when?
A
- Lower airways with no cartilage
- Only occurs in forced expiration
22
Q
What opposes airway collapse in lower airways?
A
- Radial traction from interdependence
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
24
Q
What is Ohm’s Law?
A
Voltage = Current x Resistance
25
How does Ohm's Law apply to movement of air?
- Voltage- pressure difference
- Current- perfusion/flow (Q)
- Resistance (R)
- Pressure difference- QR
26
What increases resistance?
Force of breathing
27
What is lung compliance?
- 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
What is lung resistance?
- Resistance to movement of air through the airway
- Increased in asthma and COPD (obstructive lung disease)
- Airflow becomes problematic
- Investigated through spirometry
29
What is spirometry?
- Measurement of pattern of air movement into and out of lungs
- During controlled ventilatory manoeuvres
- Often does as a maximal expiratory manoeuvre
30
What can spirometry measure?
- Both resistance and compliance
| - Will record FEV1 and FVC
31
What are spirometry results dependent on?
- Results dependent on mechanical ability of lung and factors which alter resistance
- Which can also be mechanical
32
What is the forced vital capacity?
- Total volume of air that can be exhaled forcefully from full inflation (TLC) measured in litres
33
How long does it normally take for the majority of FVC to be exhaled?
- less than 3 seconds
| - Often prolonged in obstructive diseases
34
What is FEV1?
- Volume that can be forcefully expired from full inflation (TLC) in the first second
- Measured in litres
- Resistance
35
What is the normal FEV1?
- 70-80% of FVC in the first second
- Athletes and physically may achieve more
- Those with respiratory disease may do less
36
What is the classification of severity of FEV1 interpretation?
- >75%- Normal
- 60-75%- mild obstruction
- 50-59%- moderate obstruction
- <49% severe obstruction
37
What is the classification of severity of FVC interpretation?
- 80-120%- Normal
- 70-79%- mild reduction
- 50-69%- moderate reduction
- <49% severe reduction
38
Why is full inflation important?
- Maximal can allow for a reproductive test
- Also leads to the least possible resistance
- Best possible flow
39
What are the patterns in spirometry that reflect obstruction?
- Long flow
| - All air will come out due to higher resistance
40
What are the patterns in spirometry that reflect restriction?
- FEV1 drops in proportion to normal
- Smaller amount of air exhaled
- Appropriate percentage FVC1 is removed
41
What are obstructive disorders characterised by?
- Low expiratory flow
| - Typically due to increased resistance
42
How does obstructive disorders present?
- 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
Describe asthma
- 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
Describe chronic obstructive pulmonary disorder (COPD) (bronchitis)
- excessive mucous production in airway
- leads to mucous plugging, inflammatory cell infiltration and oedema
- All of which can impede airflow, leading obstruction
45
Describe chronic obstructive pulmonary disorder (COPD) (emphysema)
- 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
What are restrictive conditions characterised by?
- Diminished lung volume
| - Typically this is due to decreased compliance and so decreasing inspiration
47
Why is compliance decreased in restrictive conditions?
- 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
Describe pulmonary fibrosis
- 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
Give examples of conditions that lead to pulmonary fibrosis
- Interstitial lung disease, asbestosis, idiopathic pulmonary fibrosis, farmer's lungs and pigeon fancier's lung
50
What is heart failure?
- Failure to eject sufficient blood from the left ventricle
| - Also fails to clear it from lungs
51
What happens to the lungs during heart failure?
- Lungs become engorged with blood as it becomes congested
- Lungs become stiffer and harder to inflate
- Increased resistance- obstruction
- Decreased compliance- restriction
52
What do flow volumes loops provide?
- Graphical illustration of a patients spirometric
53
Describe flow volume loops
- 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
Why would having a non-maximal inspiration result in invalid results?
- Maximal inspiration was vital to get best flow
| - Here flows will appear reduced and may present, wrongly, as restrictive
55
Why could coughs result in invalid results?
- Can give a false indication of both FEV1 and FVC
| - Any variable including a cough should be ignored
56
Why would sub-maximal result in invalid results?
- By definition obstruction is a reduced expiration
| - As such poor technique appears obstructive
57
Why would early termination result in invalid results?
- 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
Why would a partially obstructive mouthpiece result in invalid results?
- 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
Why would a leak result in invalid results?
- 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
