Respiratory Function Tests

Question 1

What are the limitations of lung function tests?

Answer 1

Patients may be unable to perform the test, or unable to understand the instructions

Question 2

What is involved in spirometry?

Answer 2

Spirometry involves maximal effort by the individual and volume is plotted against time

Question 3

What is measured in a spirometry trace?

Answer 3

Volume is plotted against time

Question 4

How will an obstructive lung disorder affect FEV1/VC?

Answer 4

FEV1 is reduced more than the vital capacity as there are issues associated with expiration as the blockage will become more lodged on expiration than on inspiration, but there are no issues that affect the actual available lung volume. Therefore, FEV1 is smaller but VC remains the same and therefore the FEV1/VC is reduced.

Question 5

How will a restrictive lung disorder affect the FEV1/VC?

Answer 5

In restrictive lung disease, the vital capacity is reduced due to reduced chest expansion or lung fibrosis which reduces the amount of available lung volume. FEV1 isn’t really affected, and therefore FEV1 is divided by a smaller number, and therefore the ratio is elevated in this form of disorder.

Question 6

How can you calculate FEV1 from a spirometry trace?

Answer 6

As volume is plotted against time, you ask the patient to breath out as quickly and as powerfully as they can, and then you will see the maximum volume that they managed to exhale in the timeframe of 1 second from exhalation onset

Question 7

What conditions reduce peak flow?

Answer 7

Reduced in large airway obstruction, upper airway obstruction and asthma (OBSTRUCTIVE LUNG DISORDERS)

Question 8

How would small airways disease present on a flow-volume loop?

Answer 8

There will be ‘scooping out’ of the expiratory portion of the flow-volume loop as expiration is mainly implicated by this obstructive disorder

Question 9

What type of disorder is small airways disease?

Answer 9

Obstructive disease

Question 10

Physiologically, which should be larger: maximal inspiratory flow or maximal expiratory flow?

Answer 10

Maximal expiratory flow as this is accompanied by compression of the alveoli and therefore this increases the flow rate.

Question 11

What are examples of small airway disease?

Answer 11

These are obstructive respiratory diseases and include emphysema and asthma

Question 12

How would restrictive lung disease present on a flow-volume loop?

Answer 12

The flow-volume loop is the same shape but is narrower as a result of decreased lung volumes

Question 13

What is variable extra thoracic obstruction?

Answer 13

An obstruction that occurs outside of the thorax

Question 14

What causes variable extra thoracic obstruction?

Answer 14

Unilateral vocal cord paralysis or dysfunction as this causes the vocal cord to move passively with the pressure gradient across the glottis. Therefore, during forced inspiration it’s drawn in and causes a plateau in inspiratory flow whereas in forced expiration it is passively forced aside and therefore expiratory flow is unimpaired

Question 15

How does variable extra thoracic obstruction appear on a flow-volume loop? (unilateral vocal cord paralysis or dysfunction)

Answer 15

The inspiratory flow-loop will be plateaud due to impeded forced inspiration but expiratory flow isn’t impaired and therefore appears normal.

Question 16

What is variable intrathroacic obstruction?

Answer 16

In forced inspiration the negative pleural pressure keeps the trachea opening, but in the absence of this pressure in forced expiration this causes tracheal narrowing when there is a lack of structural support, and therefore this impedes expiratory flow

Question 17

What causes variable intrathoracic obstruction?

Answer 17

Tracheomalacia (floppy trachea)

Question 18

How does variable intra thoracic obstruction (tracheomalacia) appear on a flow-volume loop?

Answer 18

Inspiration is normal as the negative pleural pressure keeps the trachea open, but expiration peak as and then plateaus due to tracheal narrowing as pressure decreases.(due to lack of structural support to hold the trachea open)

Question 19

What is fixed intrathoracic obstruction?

Answer 19

This is where there is permanent non-variable obstruction in the thorax that impedes airflow

Question 20

What causes fixed intrathoracic obstruction?

Answer 20

Goitre and tracheal stenosis

Question 21

How does fixed intrathoracic obstruction appear on a flow-volume loop?

Answer 21

There is decreased and plated inspiratory and expiratory flow, and therefore the flow-volume loop looks rectangular

Question 22

How can you measure gas transfer in the lungs?

Answer 22

A single, large breath of air with carbon monoxide and helium in it, that is held for 10 seconds, allows the alveolar volume and gas transfer to be calculation.

Question 23

What is the transfer factor of the lung for carbon monoxide (TLCO)?

Answer 23

This is indicative of the total diffusing capacity of the lung

Question 24

What is the Fick principle?

Answer 24

The volume of gas per unit time (flow) which diffuses across a tissue sheet is proportional to the area of the sheet, inversely proportional to sheet thickness, and is proportional to the difference in pressure on the two sides and dependent on the permeability coefficient for that gas.

Question 25

How may disease reduced gas transfer by the Fick principle?

Answer 25

> Reduced ‘sheet’ surface area - this occurs if there is surgical removal of lung tissue or reduced effective area due to emphysema, or if there are increased amounts of ‘dead space’
Increased ‘sheet’ thickness - this can occur with pulmonary fibrosis and alveolar proteinosis in acute lung injury
Reduced pressure difference - this is seen in high altitude

Question 26

What is meant by the airway resistance?

Answer 26

The pressure different between the alveoli and the mouth

Question 27

How does emphysema effect lung compliance and elastic recoil?

Answer 27

Increases lung compliance but reduces elastic recoil

Question 28

How does lung fibrosis effect lung compliance and elastic recoil?

Answer 28

Decreases compliance but increases elastic recoil

Question 29

Which region of the lungs is best ventilated and perfused?

Answer 29

The lung bases