Lecture 6.2: Lung Function Testing

Question 1

What is included in the Lung Function Report? (9)

Answer 1

• Vital Capacity
• FEV1 (before and after bronchodilators)
• FEV1/FVC ratio
• Peak Expiratory Flow Rate
• FRC
• RV
• TLC
• RV/TLC
• Transfer factor (carbon monoxide conductance)

Question 2

Why is Lung Function Testing done?

Answer 2

• The mechanical condition of the lungs
• Resistance of the airways
• Diffusion across alveolar membrane

Question 3

Volume: What is Vital Capacity?

Answer 3

Maximum Inspiration to Maximum Expiration

Question 4

What limits Vital Capacity? (2)

Answer 4

Maximum Inspiration:
• Compliance of the lungs
• Force of inspiratory muscles (diaphragm, intercostal muscle)

Maximum Expiration:
• Increasing airway resistance
• As the lungs are compressed

Question 5

What is Single Breath Spirometry?

Answer 5

Subject fills lungs from atmosphere and then once connected to mouthpiece
breathes out as far and fast as possible

Question 6

What are the long forms of FEV(1) and FVC?

Answer 6

• FEV1 = Forced Expiratory Volume in 1 Second
• FVC = Forced Vital Capacity

Question 7

What is Forced Vital Capacity (FVC)? Typical Value? Determining Factors?

Answer 7

• The maximum volume that can be expired from full lungs
• Typically 5l in healthy adult
• Dependent on age, height and sex

Question 8

What is Forced Expiratory Volume in 1 Second (FEV1)? Typical Value? What can impact this value?

Answer 8

• Measures how easy it is to get air out
• A good indicator of the state of your airways
• Reduced if airways are narrowed
• Normally >70% FVC (typical values 66-83%

Question 9

What is the FEV1/FVC ratio? Typical Value?

Answer 9

• Is the ratio of the forced expiratory volume in the 1st second to the forced vital
capacity of the lungs
• The normal value for this ratio is above 0.75-85, though this is age dependent

Question 10

What do FEV1/FVC ratio values of less than 0.70 indicate?

Answer 10

Values less than 0.70 are suggestive of airflow limitation with an obstructive pattern

Question 11

What is a Restrictive Deficit? What happens to FEV1 and FVC?

Answer 11

• Lungs are difficult to fill
• They are stiff
• Weak muscles
• Problem with chest wall
• They will start less full (reduced FVC)
• But air will come out normally (normal FEV1)
• FEV1/FVC ratio is normal (or higher) – i.e. ≥ 0.7

Question 12

What is an Obstructive Deficit? What happens to FEV1 and FVC?

Answer 12

• Airways narrowed causing increased resistance in expiration
• Slower air flow (Reduced FEV1)
• No limitation to filling (FVC relatively normal)
• FEV1/FVC ratio is <0.7

Question 13

What is Peak Expiratory Flow Rate (PEFR)?

Answer 13

Peak flow measurement is a quick test to measure air flowing out of the lungs

Question 14

What is a Peak Flow Meter? What is it used for? Problems?

Answer 14

• Simple, cheap device
• Screening test for airway narrowing
• Insensitive
• Screening for asthma
• Monitoring asthma at home

Question 15

Measurement of Serial Dead Space: Nitrogen Washout

Answer 15

• Subject takes one normal breath of pure oxygen
• Breathes out via meter measuring % nitrogen
• Initially only oxygen expired from airways
• Then mixture of oxygen and air (inc Nitrogen) from alveoli
• Volume expired at transition is serial dead space
• Also used to measure (indirectly) ventilation perfusion matching

Question 16

Measurement of Residual Volume: Helium Dilution

Answer 16

• Helium not normally present in air and insoluble in blood
• A known concentration inhaled from Functional Residual capacity
• Concentration reduced by mixing with air already in lungs

Question 17

Measuring Diffusion Conductance

Answer 17

• Transfer Factor (Diffusion conductance) = How easily gas can cross the alveoli
membrane
• Pressure difference(V) = Amount of gas(I) x Resistance(R)
• CO used because it has no partial pressure in capillary and easily diffuses
across alveolar membrane