Lung Function Tests

Question 1

What are some of the types of pulmonary function tests?

Answer 1

• Spirometry and flow volume loops
• SpO2
• End tidal CO2
• Maximum inspiratory/expiratory pressures
• Sleep studies

Question 2

Why is spirometry performed?

Answer 2

Because impaired ventilatory function is one of the most common physiological abnormalities affecting the lung

Question 3

What are some of the indications for spirometry?

Answer 3

• Respiratory disease
• Differentiating respiratory from cardiac disease
• Differentiating obstructive from restrictive disease
• Assessing response to treatment
• Preoperative risk stratification

Question 4

What is vital capacity?

Answer 4

The useable portion of a person’s lung volume (i.e. excludes residual volume)

Question 5

What does spirometry require?

Answer 5

Maximal effort inspiration/expiration and patient cooperation

Question 6

What is forced vital capacity (FVC)?

Answer 6

Maximum inspiration, then exhaling as fast/hard as possible - total amount of air exhaled (mLs or Ls)

Question 7

What is FEV1?

Answer 7

The forced amount of air exhaled after 1 second when measuring FVC

Question 8

What does spirometry quantify?

Answer 8

Volume expelled from the lung per unit of time

Question 9

Why is the volume of gas recorded by a spirometer less than that displaced by the lungs?

Answer 9

• Because the spirometer is cold compared to the lungs (20 degrees vs. 37 degrees)
• Gas shrinkage at lower temps
• Condensation of water vapour

Question 10

What are the major factors that affect spirometry?

Answer 10

• Age: increases with age until 20 (f) or 25 (m), then decreases
• Gender: males > females
• Height
• Ethnic origin: caucasian > african > chinese > polynesian

Question 11

What is the normal % of predicted value for FEV1 & FVC?

Answer 11

80-120% of predicted value, abnormal = < 80%

Question 12

What are the normal ranges for FEV1 & FVC?

Answer 12

FEV1: 3.64-5.46
FVC: 4.49-6.73

Question 13

What FEV1/FVC ratio indicates significant airway obstruction?

Answer 13

< 70%

Question 14

How is flow measured?

Answer 14

Volume/time, i.e. litres/second at BTPS

Question 15

What does quiet breathing look like on an expiratory flow volume curve?

Answer 15

A circle

Question 16

When does peak expiratory flow rate (PEFR) occur?

Answer 16

Early in forced expiration

Question 17

Why is peak expiratory flow limited in accuracy?

Answer 17

Because there is insufficient data for initial assessment

Question 18

Peak expiratory flow is used in monitoring of asthmatics to identify -?

Answer 18

• Trends in lung function
• Effects of treatment
• Trigger factors

Question 19

What do maximal expiratory manoeuvres generate?

Answer 19

Large positive intra-pleural pressure

Question 20

What is the equal pressure point?

Answer 20

The point at which pressure inside the airway equals the intrapleural pressure

Question 21

Why is flow from the lungs limited at lower lung volumes?

Answer 21

At higher volumes, there’s more traction on the airways, while at lower volumes the airways aren’t held open as well

Question 22

What is FEF 25-75%?

Answer 22

Average forced expiratory flow rate over the middle 50% of expiration (L/min)

Question 23

What is the difference between an obstructive disorder and a restrictive disorder?

Answer 23

Obstructive: Something is trapping air in the lungs, patient takes a long time to blow all their air out
Restrictive: Something is stopping air getting into the lungs, but they can blow out easily

Question 24

What causes an obstructive disorder?

Answer 24

• Bronchitis: Partial occlusion of the airway lumen
• Asthma, bronchitis: The wall of airway, i.e.e bronchial smooth muscle contraction, inflammation
• Emphysema: Destruction of the lung parenchyma

Question 25

What causes a restrictive disorder?

Answer 25

• Lung parenchyma, e.g. interstitial fibrosis
• Disease of the pleura, e.g. pleural effusion, pneumothorax
• Chest wall disorder
• Neuromuscular disorder

Question 26

What is considered to be a significant improvement of FEV1 in adults (i.e. reversibility of obstruction)?

Answer 26

> 12% or > 0.2L

Question 27

How is the degree of obstruction quantified?

Answer 27

• FEV1/FVC < 75% = mild
• FEV1/FVC < 60% = moderate
• FEV1/FVC < 40% = severe

Question 28

What values indicate the presence of a restrictive disorder?

Answer 28

• FEV1/FVC > 70% (indicates normal or supra-normal)
• Plus FVC < 80%
• FEV1 may be normal or < 80% if more severe restriction

Question 29

What values indicate the presence of an obstructive disorder?

Answer 29

• FEV1/FVC < 70%
• Plus FEV1 < 80%
• FVC may be normal or < 80% if severe obstruction

Question 30

What does the volume time curve look like for a patient with an obstructive disorder?

Answer 30

Long & flat (patient takes a long time to get the air out of their lungs)

Question 31

What does the volume time curve look like for a patient with a restrictive disorder?

Answer 31

Very short (i.e. all air is out of the lungs in a very short amount of time due to patient not being able to achieve a high VC - cannot inspire maximum volumes)

Question 32

What is the flow volume loop look like for a patient with an obstructive disorder?

Answer 32

• Concavity in expiration

- Due to small airways collapsing (not enough traction around the airways)

Question 33

What is the flow volume loop look like for a patient with a restrictive disorder?

Answer 33

• More short & round

- Due to patient not being able to get enough air into their lungs initially

Question 34

What do increased FRC and increased RV represent?

Answer 34

• FRC: Hyperinflation (loss of elastic recoil)

- RV: Air trapping (airway closure)