Lung function testing

Question 1

Why do we measure lung function?

Answer 1

• Evaluation of breathlessness
• Screening for COPD or occupational lung disease
• Pre op assessment
• Lung cancer - fitness for treatment
• Disease progression and treatment response
• Monitoring of drug treatment toxic to the lungs
• Pulmonary complications of systemic disease

Question 2

How would you explain how to do spirometry for a patient?

Answer 2

• Take a big breath in as far as you can and blow out as hard as you can for as long as possible then take a big breath all the way in
• Best of 3

Question 3

What are the pitfalls of spirometry?

Answer 3

• Requires an appropriately trained technician
• Effort and technique dependent
• Patient frailty
• Pain, patient too unwell

Question 4

What is tidal volume?

Answer 4

Volume of air breathed in and out in a single breath

Question 5

What is inspiratory reserve volume?

Answer 5

volume breathed in by max inspiration at end

of normal inspiration

Question 6

What is expiratory reserve volume?

Answer 6

volume of air expelled by max effort at the end

of normal expiration

Question 7

What is residual volume?

Answer 7

Volume of air in the lungs at the end of maximum expiration

Question 8

What is inspiratory capacity?

Answer 8

maximum volume of air inspired after a normal expiration

Question 9

What is vital capacity?

Answer 9

The volume of air that can be breathed in after a maximum expiration

Question 10

What is the normal FEV1/FVC ratio?

Answer 10

> 70%

Question 11

What spirometry results suggest an obstructive lung disease?

Answer 11

• FEV1/FVC ratio <70%

* Reduced FEV1

Question 12

What is the severity of COPD stratified by in terms of spirometry results?

Answer 12

Stratified by % predicted FEV1
•Mild >80%
•Moderate 50-80%
•Severe 30-50% 
•Very severe <30%

Question 13

What is reversibility testing?

Answer 13

• Nebulised or inhaled salbutamol is given
• Spirometry performed before and 15 minutes after salbutamol
• 15% and 400ml reversibility in FEV1 is suggestive of asthma

Question 14

Aside from spirometry, what tests can be done to investigate asthma?

Answer 14

•PEFR testing
- look for diurnal variation and variation over time
- Response to inhaled corticosteroid
- Occupational asthma
•Bronchial provocation
•Spirometry before and after trial of inhaled/oral corticosteroid

Question 15

What are the spirometry results suggestive of a restrictive lung disease?

Answer 15

• It will have the same curve but will just be smaller as a regular spirometry result
• FEV1 and FVC reduced
• FEV1/FVC ratio >70%

Question 16

What are the causes of restrictive spirometry results?

Answer 16

• Interstitial lung disease
• kyphoscoliosis/ chest wall abnormality
• Previous pneumonectomy
• Neuromuscular disease
• Obesity
• Poor effort/technique

Question 17

Describe the test for measuring transfer factor

Answer 17

• Single breath of a very small concentration of carbon monoxide
• CO has a high affinity to Hb
• Measure concentration in expired gas to derive uptake in the lungs

Question 18

What is transfer factor affected by?

Answer 18

• Alveolar surface area
• Pulmonary capillary blood volume
• Haemoglobin concentration
• Ventilation perfusion mismatch

Question 19

What is transfer factor reduced in?

Answer 19

• Emphysema
• Interstitial lung disease
• Pulmonary vascular disease
• Anaemia (increased in polycythaemia)

Question 20

What are the methods of measuring lung volumes?

Answer 20

• helium dilution (inspire a known quantity of an inert gas)
• Body plethysmography

Question 21

What are the effects of restrictive and obstructive lung diseases on lung volumes?

Answer 21

• Lung volumes reduced in restrictive lung disease

* Increased reserve volume and total lung capacity in obstructive lung disease

Question 22

What does a reliable oximetry result depend on?

Answer 22

Adequate perfusion

Question 23

What are the main causes of hyperaemia?

Answer 23

• Hypoventilation (e.g. drugs, neuromuscular disease)
• Ventilation/perfusion mismatch (e.g. COPD, pneumonia)
• Shunt (e.g. congenital heart disease)
• Low inspired oxygen (altitude, flight)

Question 24

What is ventilation perfusion mismatch?

Answer 24

• Happens to a degree in normal lungs (bottom better perfused, top better ventilation)
• Areas of the lung that are well perfused and not well ventilated
• Mixing of blood from poorly ventilated and well ventilated parts of the lung causes hypoxaemia