Basic Lung Function Testing

Question 1

Why is testing lung function useful?

Answer 1

Useful in symptomatic or patients at risk of pulmonary disease.
Uses:
- Evaluation of lung function patterns provides aid to diagnosis
- Can follow changes in lung function e.g. normal compared to treatment
- Assess changes in response to specific stimuli

Question 2

What is measured in Lung function tests?

Answer 2

Air flow rate = measures diameter of airways
Vital capacity = vol. from max. inhalation to max. exhalation = measure total lung volume
V/Q matching = measure how quickly gas diffuses into blood

Question 3

How is peak flow used to asses lung function?

Answer 3

• Easy to perform
• Cheap equipment (peak flow meter + diary to record values/symptoms)
• Max. achievable flow determined by diameter of bronchial tree + muscle power available (L/min)

Question 4

How is peak flow performed?

Answer 4

• Sit in comfortable position (same every time)
• How peak flow meter horizontally
• Deep breath out then deep breath in
• Wrap lips tightly round mouthpiece
• Blow from max. inhalation so muscles + bronchioles are at max. diameter
• Air flow not limited as airways open
• Quick, sharp, hard single breath out into peak flow meter
• Check reading

Question 5

What different inhalers can be given?

Answer 5

1. Reliever - beta (sympathetic) antagonist, opens airways directly + gives immediate relief
2. Preventer - reducing inflammation, long-term treatment

Question 6

Explain the principles of Spirometry

Answer 6

Includes measurement of forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC)

Question 7

What are the advantages/disadvantages of spirometry?

Answer 7

Advantages:

• readily available
• most useful test
• takes 10-15 mins
• internationally accepted criteria (ensures results are optimal + repeatable)
• high utility

Disadvantages:

• uses £800 equipment
• requires trained technician
• results heavily relied on

Question 8

What does forced vital capacity (FVC) measure?

Answer 8

Measure from max. inspiration to max. expiration

Good indicator of total lung volume + flow

Question 9

What is residual capacity/volume?

Answer 9

Volume of air left in lungs after FVC (difficult to measure)

Question 10

What is the flow volume loop?

Answer 10

Not the same flow volume as measured with peak flow meter as it is not a forced volume

Flow volume increases drastically with inhalation and then drops dramatically as lungs/airways get narrower/smaller (diameter becomes only limiting factor)

Question 11

What is Restrictive Spirometry?

Answer 11

Small airways = restricted so spirometric pattern = restrictive

Reduction in vital capacity = best index of lung restriction (measured from full inspiration with forced exhalation until cannot exhale further)

Used to support clinical working diagnosis but not used in isolation

Question 12

What is the most common cause of restrictive spirometry?

Answer 12

Failure to breathe out fully during test

Question 13

What is the flow like in lung restriction?

Answer 13

Flow maintained as lungs airways aren’t restricted BUT FVC is affected (decreases)

Question 14

If airways are narrowed, time taken to empty lungs (exhalation) will…

Answer 14

Increase

Question 15

How do you get a wheeze?

Answer 15

Amount of air breathed out 1 sec in hard exhalation will thus be reduced + airway narrowing results in turbulent flow (due to obstruction)

Question 16

What signs would show airway obstruction?

Answer 16

Residual volume increase (more air trapped behind obstructed bronchi at end of expiration)
Barrel shaped (hyper inflated chest)

Question 17

What can affect FEV1 and FVC?

Answer 17

Height
Weight
Age
Sex
Ethnicity

Question 18

What is normal FEV1 and FVC?

Answer 18

> 80% of predicted

Question 19

What happens to the ratio of FEV1:FVC in a) normal b) obstructive lung disease c) restrictive lung disease?

Answer 19

a) ~0.7 (not strict)
b) <0.7 as FEV1 reduced more than FVC
c) >0.7 as FVC reduced more than FEV1

Question 20

What is Diffusion Lung Capacity for Carbon Monoxide (DLCO)?

Answer 20

• Can directly measure rate at which CO diffuses across lung membranes into blood to assess permeability of entire respiratory system.
• Can then be compared to normal values for population and expressed as percentage of normal
• Both restrictive + obstructive lung diseases can reduce diffusion capacity.