Lung Function Tests

Question 1

How would you use lung function tests

Answer 1

Diagnosis and monitoring of

• disease progression
• risk stratification
• treatment response

Question 2

What are the 4 routine LFTs

Answer 2

Spirometry
Lung volume
Gas transfer
Volitional resp muscle strength

Question 3

What are the 4 specialist LFTs

Answer 3

Exercise bronchial provocation
Exhaled biomarkers
Lung mech, forced oscillations
Non volitional resp muscle strength

Question 4

What are some examples of

• airway
• chest wall
• lung
• muscle
• thoracic cavity
• pulmonary vasculature diseases

Answer 4

Airway

• Asthma
• CODP
• Bronchiolitis

Chest wall

• Scleroderma
• Kyphoscoliosis
• Pregnancy
• Obesity

Lung

• IPF
• Tumour
• Resection
• Collapse

Muscle

• Polio
• NMD
• Phrenic palsy

Thoracic cavity

• Cardiomegaly
• Effusion
• Tumour

Pulmonary vascular diseases

• PE
• HF

Question 5

What are the characteristics of obstructive illnesses

What are some examples

Answer 5

Decreased airflow due to lumen obstruction
Airway wall changes
Airway support loss
Ext compression

Asthma
COPD
Bronchiectasis
Bronchiolitis
CF

Question 6

What are the characteristics of restrictive illnesses

What are some examples

Answer 6

Decreased lung volume
Abnormal lung parenchyma
Abnormal chest wall
Weak resp muscles
Abnormal pleura

Fibrosis
Kyphoscoliosis
DMD
Phrenic palsy
Obesity

Question 7

What are the characteristics of mixed illnesses

Answer 7

Decreased airflow and lung volume

SCD
Idiopathic fibrosis + emphysema

Question 8

How would you differentiate between obstructive and restrictive lung disease on a flow volume loop

Answer 8

Obstructive
-concave shape on expiration as airways collapse

Restrictive
-similar shape to normal loop but smaller

Each disease has its own characteristic shape

Question 9

How would you differentiate between obstructive and restrictive lung disease on spirometry
What can you not diagnose via spirometry

Answer 9

Obstructive

• FEV1 < 0.8
• FRC reduced slightly
• FEV1/FRC <0.7

Restrictive

• FEV1, reduced
• FRC, reduced
• FEV1/FRC normal

Cannot diagnose restrictive diseases
-in obstructive diseases, airways collapse on themselves so FRC may be reduced. Can look restrictive

Question 10

What is the reversibility test

How would you differentiate between asthma and COPD

Answer 10

Repeat spirometry after BD
-Increased FEV1 > 12% => significant reversibility

Asthma, significant reversal
COPD, relief due to some deflation but no significant reversal

Question 11

What are the definitions of

• RV
• TLC
• FRC

How would you measure lung volume

Answer 11

RV
-vol after max expiration
TLC
-vol after max inspiration
FRC
-vol after relaxed expiration

Gold standard
Body plethysmograph
Inert gas dilution

N2 washout
CXR planimetry
volume CT
USS

Question 12

What are the causes of increased FRC, RV

• intrapulmonary
• extrapulmonary

Answer 12

Intrapulmonary
-airway obstruction

Extrapulmonary
-resp muscle weakness

Question 13

What are the causes of increased TLC

Answer 13

Emphysema

Question 14

What are the causes of decreased TLC

• intrapulmonary
• extrapulmonary

Answer 14

Intrapulmonary

• Pneunectomy
• Atlectasis
• Consolidation
• Edema
• Fibrosis

Extrapulmonary

• pleural disease
• ribcage issues
• resp muscle issues
• obesity

Question 15

What is the transfer coefficient
What is it a measure of

What factors does the TLCO depend on

• alveolar mv
• Hb binding

Answer 15

KCO=TLCO/Va
Gas uptake/litre of vent lung

gas transfer from lung to Hb
Alveolar mv
-SA
-conc change
-solubility
-MW

Hb binding

• [Hb]
• perfusion
• PO2

Question 16

How would you judge if your LFT or SR reading is abnormal

What are the different stages or abnormality from SR

Answer 16

LFT
-% of predicted value

SR
-no of SDs from PV

Mild
+- 1.65 - 2.5

Moderate
+-2.51 - 3.5

Severe
+-3.51