Resp10 - Spirometry & Lung Function Tests

Question 1

What is a spirometer used for?

Answer 1

Spirometer is used to measure and record volumes of inspired and expired air
- the graph produced is a spirogram

• inspiration produces an upwards deflection
• expiration produces a downwards deflection

Question 2

Definitions of of Lung Volumes and Capacities

Tidal Volume
Inspiratory Reserve Volume (IRV)
Expiratory Reserve Volume (ERV)
Residual Volume (RV)

Inspiratory Capacity
Functional Residual Capacity
Vital Capacity
Total Lung Volume

Answer 2

Tidal Volume - volume of air entering and leaving the lungs with each breath

Inspiratory Reserve Volume - maximum volume of extra air that can be breathed in during forced inspiration
Expiratory Reserve Volume - maximum volume of extra air that can be breathed during forced expiration
Residual Volume - air left in lungs after forced expiration

Inspiratory Capacity - from end of quiet expiration to maximum inspiration (tidal volume + IRV)
Functional Residual Capacity - volume of air at the end of quiet expiration (ERV + RV)

Vital Capacity - maximum volume of air that can be breathed in and out (tidal volume + IRV + ERV)
Total Lung Volume - maximum volume of air that can be breathed in and ‘thoretically’ breathed out (vital capacity + RV)

Question 3

5 ways forced flow-volume measurements can be used

Answer 3

1.) Type of Disorder - restrictive or obstructive
- volume and speed of air breathed out
- shape of the spirogram

2.) Site of Obstruction - can be seen by pattern of change in the flow-volume curve

3.) Response to Treatment - e.g. B2 agonists

4.) Change with age/growth

5.) Progression of Disease

Question 4

Forced Vital Capacity (FVC), Forced Expiratory Volume 1 (FEV1), Peak Expiratory Flow (PEF)

Answer 4

1.) FVC - forced vital capacity
- maximal amount of air that can be forcibly exhaled after taking a maximal inhalation
- can be predicted using gender, age, height, ethnicity

2.) FEV1 - forced expiratory volume in the first second
- most reproducible flow parameter so used in managing obstructive disorders (asthma, COPD)

3.) PEF - peak expiratory flow
- maximal speed of airflow during exhalation

Question 5

3 features of volume-time graphs in obstructive diseases (asthma, COPD)

FVC
FEV1
FEV1:FVC

Answer 5

1.) FVC Nearly Normal - if given sufficient time to breathe out, FVC is not markedly reduced

2.) FEV1 Markedly Reduced - narrowed airways reduces the speed air can be breathed out

3.) FEV1:FVC Ratio - will be < 70% of normal (predicted) values

4.) Obstructive Diseases
- Asthma and COPD
- bronchiectasis
- bronchiolitis obliterans

Question 6

3 features of volume-time graphs in restrictive diseases (lung fibrosis)

FVC
FEV1
FEV1:FVC

Answer 6

1.) FVC Markedly Reduced - stiff lungs can’t fully expand

2.) Reduced FEV1 - naturally decreases

3.) FEV1:FVC Ratio - will be > 70% of normal
- speed at which air can be breathed out is still normal because of no narrowing of airways

4.) Restrictive Diseases
- pulmonary fibrosis, asbestosis, sarcoidosis
- respiratory distress syndrome
- Neuromuscular disorders
- Severe obesity
- Kyphoscoliosis e.g. ankylosing spondylitis

Question 7

4 features of a flow-volume loop

Axes
Peak Expiratory Flow
Vital Capacity
Scalloping

Answer 7

1.) Axes - volume on x axis, flow on y axis
- expiration above the x axis, inspiration below (-ve)
- read the graph like a clock

2.) Peak Expiratory Flow - highest point on expiration
- air is flowing through the wide airways so greatest flow
- flow decreases due to air entering small airways
- if this is very low (circular graph), suggests a fixed extra-thoracic obstruction

3.) Vital Capacity - measured off the x axis
- larger vital capacity suggests upper airway obstruction
- shorter vital capacity suggests restrictive lung disease

4.) Scalloping - descending line from PEF is not linear and contains an indent
- suggests obstructive disease (asthma, COPD), COPD produces more significant scalloping