S6) Lung Function Testing

Question 1

What is residual volume?

Answer 1

Residual volume is the volume of air still remaining in the lungs after the expiratory reserve volume is exhaled

Question 2

What is the reason for a residual volume in the lungs?

Answer 2

We cannot empty our lungs completely, so after a forced expiration a residual volume will remain

Question 3

Lung capacities are defined relative to fixed points in the breathing cycle.

What are these?

Answer 3

• Maximum inspiration
• Maximum expiration
• End of quiet expiration

Question 4

What is the purpose of spirometry?

Answer 4

Spirometry measures the movement of air during breathing as well as measuring lung volumes and capacities

Question 5

What is vital capacity?

Answer 5

Vital capacity is the total amount of air that can be expired after fully inhaling (inspiratory reserve volume + tidal volume + expiratory reserve volume)

Question 6

Vital capacity depends on maximal inspiration and maximal expiration.

Why may it be reduced?

Answer 6

• Lungs are not filled normally in inspiration
• Lungs are not emptied normally in expiration

- Or both

Question 7

What is a time-volume graph?

Answer 7

In spirometry, a time-volume graph is a graph which plots volume of air exhaled against time.

Question 8

What determines the maximal filling of the lungs?

Answer 8

Maximal filling of the lungs is determined by the balance between maximum inspiratory effort and the force of recoil of the lungs

Question 9

How is a restrictive deficit produced?

Answer 9

A restrictive deficit is produced when lungs are unusually stiff or inspiratory effort is compromised by muscle weakness, injury/deformity

See spirometry volume-time curve below:

Question 10

How is an obstructive deficit produced?

Answer 10

An obstructive deficit is produced when airways are narrowed resulting in compromised expiratory flow much earlier in respiration

Question 11

How are obstructive and restrictive deficits distinguished?

Answer 11

Distinguished by measuring the FEV1:FVC

Question 12

What is FEV1?

Answer 12

FEV1 is the forced expiratory volume in one second

Question 13

What is FVC?

Answer 13

Forced vital capacity is the amount of air which can be forcibly exhaled from the lungs after taking the deepest breath possible

Question 14

What is the Tiffeneau-Pinelli index (FEV1/FVC ratio) ?

Answer 14

• It is a calculated ratio used in the diagnosis of obstructive and restrictive lung disease
• It represents the proportion of a person’s vital capacity that they are able to expire in the first second of forced expiration to the full vital capacity

Usually, FEV1/FVC ratio > 70%

Question 15

Describe FVC and FEV1 in an obstructive defect

Answer 15

• FVC is nearly normal
• FEV1 is reduced markedly
• FEV1/FVC ratio < 70%

Question 16

Describe FVC and FEV1 in an restrictive defect

Answer 16

• FVC is reduced
• FEV1 is reduced proportionately
• FEV1/FVC ratio ≥ 70%

Question 17

What is an expiratory flow volume loop?

Answer 17

In spirometry, an expiratory flow volume loop is a graph which plots expiratory flow rate against lung volume

Question 18

What is PEFR?

Answer 18

- Peak expiratory flow rate is a person’s maximum rate of expiration, as measured with a peak flow meter

• This occurs early in expiration as the airways are stretched to the largest diameter

Question 19

Describe the normal expiratory flow in the lungs

Answer 19

As expiration continues, the small airways are narrowed by the compression of the lungs which increases flow resistance to the point where no more air can be driven out of the alveoli

Question 20

Obstructive deficits may be more senstively revealed by deriving an expiratory flow volume loop.

Why is this?

Answer 20

Where there is small airway obstruction, this narrowing produces a characteristic, early fall in expiratory flow rate

Question 21

In normal individuals, what most affects PEFR?

Answer 21

PEFR is mostly affected by the resistance of large airways

Question 22

Identify an obstructive respiratory deficit

Answer 22

Asthma

Question 23

How can the mild obstruction of small airways be observed?

Answer 23

Mild obstruction leads to the ‘scalloping’ of the flow volume curve

Question 24

How can one measure residual volume?

Answer 24

Residual volume can be measured using the helium dilution test

Question 25

How can one measure dead space?

Answer 25

Dead space can be measured using the **nitrogen washout method**

Question 26

What is diffusion conductance?

Answer 26

**Diffusion conductance** is the resistance to diffusion across the alveolar membrane

Question 27

How can one measure diffusion conductance?

Answer 27

Diffusion conductance is measured using the **carbon monoxide transfer factor**