Basic lung function testing

Question 1

Define peak expiratory flow rate.

Answer 1

The maximum flow rate generated during a forceful exhalation, starting from full lung inflation

Question 2

Describe how a patients peak expiratory flow rate would be tested.

Answer 2

Using a peak flow meter, which registers the flow of air in L/min.

The patient takes a large inhalation followed by a forceful expiration.

This is repeated 3 times and the highest value is recorded

Question 3

In asthma, how do peak flow reading change during the day? What is this caused by?

Answer 3

Peak expiratory flow rate readings are usually lower earlier in the morning

Caused by cortisol being lower at night, and so lung inflammation worsens overnight

Question 4

Define forced vital capacity (FVC).

Answer 4

The total volume exhaled with maximal effort after a full inspiration

Question 5

Define forced expiratory volume in 1 second (FEV1).

Answer 5

The volume of air expelled in the first second of a forced expiration, starting from full inspiration

Question 6

Define FEV1/FVC ratio.

Answer 6

The proportion of FVC exhaled in the first second

Question 7

In a healthy individual, what percentage of air is exhaled in the first second in FEV1/FVC?

Answer 7

80% - meaning FEV1/FVC ratio is 0.8

Question 8

Which 2 categories of lung disorders can spirometry test for?

Answer 8

Obstructive

Restrictive

Question 9

In obstructive disorders, which part of spirometry will be different?

Answer 9

There will be a reduced FEV1

FVC can be normal or reduced

Overall, FEV1/FVC ratio is reduced – typically <0.7

PEFR will also be reduced

Question 10

Describe the shape of the effort-independent part of the curve on a flow-volume loop of someone with an obstructive disorder.

Answer 10

Concave

Question 11

In restrictive disorders, which part of spirometry will be different?

Answer 11

FVC is reduced

FEV1 can be normal or reduced, and FEV1/FVC ratio is normal or increased

Question 12

Which volume and two capacities cannot be measured using spirometry?

Answer 12

Residual volume

Functional residual capacity

Total lung capacity

Question 13

What are 3 ways you can measure residual volume and functional residual capacity?

Answer 13

Helium dilution

Nitrogen washout

Body plethysmography

Question 14

What is functional residual capacity?

Answer 14

The volume of air in the lungs at the end of a normal tidal breath

Question 15

List 3 reasons why functional residual capacity is important.

Answer 15

Oxygen buffer – allows gas exchange to continue between breaths

Prevents alveolar collapse

Optimal lung compliance

Question 16

In people with normal lung function, what should the % residual volume to total lung capacity be less than?

Answer 16

<40%

Question 17

What does diffusing capacity measurement measure?

Answer 17

The ability of the lungs to transfer gas between inhaled air and capillary blood, and for that gas to combine with haemoglobin

Question 18

Which gases are used in diffusing capacity measurements and why?

Answer 18

Carbon monoxide – it has a high affinity for haemoglobin + doesn’t dissolve in plasma

Helium – does not cross the alveolar-capillary membrane and so is used as a single breath estimate of total lung capacity