Basic Lung Function

Question 1

Why test lung function?

Answer 1

Useful in conjunction with patient history and clinical examination.

Symptoms appear once patients are down to around 60% of lung function- lung function tests can be used to assess declining lung function in asymptomatic patients and provide education.

Question 2

What does histamine cause?

How can it be used in assessment of lung function?

Answer 2

Patient complains of respiratory symptoms but lung function appears normal when assessed (e.g. asthma- airways return to normal when well).

Histamine can be given to check responsiveness of airways.

Question 3

What is air flow rate a good measure of?

Answer 3

Airway diameter

Question 4

What is the vital capacity?

What does it indicate?

Answer 4

Volume from maximal inhalation to maximal exhalation.

Measures total lung volume

Question 5

What can be used to measure how quickly gases diffuse across the alveolar membrane? (V/Q matching)

Answer 5

Carbon monoxide

Question 6

What is the residual volume?

Answer 6

The volume remaining in the lungs at maximum exhalation

Question 7

What determines maximal achievable flow (on peak flow measurement)?

Answer 7

Diameter of the bronchial tree

Muscular power

Question 8

How can a peak flow chart be used to diagnose asthma?

Answer 8

>20% variability in peak flow

Question 9

What is FEV₁?

Answer 9

Forced expiratory volume in 1 second

Question 10

What measurements does spirometry use?

Why is it more accurate than peak flow?

Answer 10

FEV₁ and FVC

As patients take a long, slow breath out, lungs decrease in volume making the airways smaller. Allows measurement of flow when the only limiting factor is airway diameter and is independent of muscle power.

In peak flow, patients with high muscle mass can have deceptively high readings.

Question 11

What is the best indicator of lung restriction?

Answer 11

Reduction in vital capacity

Question 12

Explain how the following features of obstructive airways can be explained:

Wheeze

Reduced FEV₁

Barrel shaped chest

Answer 12

FEV₁ reduced: reduced airway diameter means the flow will be reduced therefore less air volume expired in 1 second.

Wheeze: Smaller airway diameter creates turbulent flow.

Barrel shaped chest:

• Air trapped behind obstructed (narrowed) airways increases residual volume
• Reduced elastic recoil of lungs means resting position of lungs is now at higher functional residual capacity- balance between elastic recoil of lungs and chest wall favours chest wall.