L5 - Principles of Spirometry

Question 1

What are the types of spirometers?

Answer 1

Piston spirometers and water bell spirometers.

Question 2

What is the equation that relates pressure to flow?

What is this equation used for?

Answer 2

• P = flow x R, where R is a constant.

- It is used to make indirect measurements of flow (or volume by integration), such as with a pneumotachograph.

Question 3

How can the volume of the lungs be measured?

Answer 3

• Using a helium dilution method.
• A volume of air with a known concentration of helium is inhaled in a closed system. After a while, the concentration of the system is remeasured and the volume of the lungs is calculated from the new concentration.

Question 4

What is the difference between restrictive and obstructive lung diseases?

Answer 4

• Restrictive diseases reduce lung volume by reducing compliance / elasticity of alveoli.
• Obstructive diseases increase airway resistance by decreasing airway diameter.

Question 5

List 2 restrictive lung diseases.

Answer 5

1 - Fibrosis.

2 - Pulmonary oedema.

Question 6

How would a restrictive lung disease appear on a spirogram?

Answer 6

• The vital capacity would be reduced.

- The FEV1:FVC ratio would be >0.8 (as a result of reduced FVC).

Question 7

How would an obstructive lung disease appear on a spirogram?

Answer 7

• FEV1 would be < 80% of FVC (the FEV1:FVC ratio would be <0.8).

Question 8

What are FEV1 and FVC?

Answer 8

• FEV1 (forced expiratory volume) is the volume of air that can be forcefully expired in one second.
• FVC (forced vital capacity) is the total volume of air that can be forcefully expired (same as vital capacity).

Question 9

How would a restrictive lung disease appear on a flow / time graph?

Answer 9

• The peak flow would be reduced.

- The descending limb would be steeper.

Question 10

How would an obstructive lung disease appear on a flow / time graph?

Answer 10

• The peak flow would be reduced.

- The descending limb would be initially steep then shallow.

Question 11

List 2 obstructive lung diseases.

Answer 11

1 - Asthma.

2 - Bronchitis.

Question 12

How does the nature of emphysema change with time?

Answer 12

• Early: Loss of alveolar elastic structure and diffusive surface area (restrictive).
• Later: Inflammation of small airways and increased resistance (obstructive).
• Even later: Loss of alveolar elastic structure / support causing a collapse on expiration (obstructive).

Question 13

What are the two forms of COPD?

Answer 13

1 - Bronchitis.

2 - Emphysema.

Question 14

Why is the descending limb of a flow time graph steeper with a restrictive lung disease?

Answer 14

Because the tissue is less elastic, so there is less outward force opposing the contracting intercostal muscles and diaphragm.

Question 15

Why is the descending limb of a flow time graph steeper with a obstructive lung disease?

Answer 15

idk yet.