2 Lung volumes and Lung function testing

Question 1

Define lung compliance

Answer 1

Lung compliance is a measure of the lung’s ability to stretch and expand

Question 2

Explain lung compliance + its features

Answer 2

It can be understood as a change in volume/change in pressure

• At higher, the lung is stiffer, hence compliance is lower and vice versa
• Lung bases are more compliant (more volume) than the apex. - better ventilation

Compliance is followed by elastic recoil

Question 3

What can cause decreased lung compliance?

Answer 3

e. g.
- Pulmonary fibrosis
- Alveolar oedema

Question 4

What influences compliance?

Answer 4

• Thoracic cage (expands during inhalation)

- Elasticity (influences stretchiness of lungs)

Question 5

What is needed for efficient ventilation?

Answer 5

• High lung compliance

- Low alveolar surface tension due to surfactant

Question 6

What is a surfactant?

Answer 6

A mixture of phospholipids, proteins, and ions, that work to reduce the surface tension in the alveoli

Question 7

Which cells secrete surfactant?

Answer 7

Type II alveolar epithelial cells

Question 8

How does surfactant work?

Answer 8

They reduce surface tension and increase the stability of the alveoli, preventing the lungs from collapsing

Question 9

GIve an example where lack of surfactant has serious consequences

(NOT IMPORTANT, but useful)

Answer 9

Infant respiratory distress syndrome (IRDS)

• In the clinic, it is seen that there is insufficient surfactant production,
• the air sacs (alveoli) collapse,
• and so the lungs are difficult to inflate

Surfactant is secreted into the alveoli between the 6th and 7th month of gestation
- IRDS is observed in premature birth and is fatal if not treated

Management:

• Pre-birth - corticosteroids (betamethasone) given to mother to speed up lung development
• Surfactant replacement therapy immediately after birth
• High levels of O2 (with caution; the baby must be monitored closely for O2 toxicity > free radicals which may damage any surfactant produced)

Question 10

What is the need for lung function testing?

Answer 10

Tests need to assess:

• Mechanical condition of lung (compliance)
• Resistance of the airways (narrowing)
• Diffusion across the alveolar membrane

Question 11

What can a spirometer measure?

dependent on the lung’s elastic properties and properties of the muscles of the chest wall

Answer 11

Tidal volume
Vital Capacity
Inspiratory Reserve Volume
Expiratory reserve volume

Question 12

What can’t a spirometer measure?

Answer 12

Total lung capacity

Residual Volume

Question 13

Define tidal volume

Answer 13

TV - the volume of air moved in and out of lungs at rest (L)

Question 14

Define vital capacity

Answer 14

VC - the maximum amount of air moved in and out of the lungs following forceful inhalation and exhalation

Question 15

Define inspiratory reserved volume

Answer 15

IRV - the extra volume of air that can be forcefully inhaled above normal tidal volume

Question 16

Define expiratory reserved volume

Answer 16

ERV - extra volume of air that can be forcefully inhaled above normal tidal volume

Question 17

Define total lung capacity

Answer 17

TLC - the total amount of air that is held in the lungs

Question 18

Define residual volume

Answer 18

RV - the total amount of air left in the lungs following forceful exhalation

Question 19

Define functional residual volume

Answer 19

FRV - the air left in the lungs following normal exhalation

Question 20

What can a vitalograph measure?

spirometer is more modern way

Answer 20

• Forced Vital capacity

- Forced expiratory volume

Question 21

Define Forced vital capacity

Answer 21

FVC - the toal volume of air exhaled forcefully (approx 5L)

Question 22

Define forced expiratory volume

Answer 22

FEV1 - the volume of air expired forcefull in the first second

typically, >70% of air forcefully expired is done in this time

Question 23

What is FVC/FEV1 used for

Answer 23

If this ratio is lower than 70%, diagnosis can be made, along with an indication of airway size, and type of deficit

Question 24

What physiological/environmentl factors affect lung volumes

Answer 24

• Anthropometric measurement (age, height, sex)
• Occupation (physical fitness; office vs athlete)
• Environment - altitude
• Standing up right vs sitting down

Question 25

How is functional residual capacity meausred? (TLC/RV) | as residual air cannot be directly expired into the spirometer

Answer 25

- Helium detection - Nitrogen washout (helium used as it is not metabolised in the blood) (can be measured, as it will not get lost) after measuring FRC, TLC and RV can be calculated

Question 26

How does Helium detection work?

Answer 26

In a closed system, there is a spirometer with a known concentration and volume of helium - Before equilibration (before breathing) - C1 (conc. of helium before breathing in) - Then participant breathes in (with helium) - Known conc. of helium is no more - So C2 is given, conc. of helium after equilibration - V1 is the volume of helium/air before equilibration (trying to find V2 – FRC representation, reflected in helium measurements) - C2 measured by spirometer equipment - Using the formula, rearrange to find V2 V2 = V1 * ([C1-C2]/C2) V2 = FRC

Question 27

How does nitrogen washout work?

Answer 27

Procedure: - Patient expires 100% O2 - Expires into the spirometer system - Procedure repeated until N2 in lungs is replaced with O2 - FRC calculated from exhaled N2 and estimated alvoelar N2

Question 28

Define restrictive deficit, and give some features of it

Answer 28

When lung expansion is compromised - may be due to alterations in the lung parenchyma, disease of the pleura, or chest wall (lungs do not fill to capacity, hence they are less full before expiration)

Question 29

What happens to FVC, FEV1, and FEV1/FVC when there is a restrictive deficit?

Answer 29

- FVC is reduced - FEV1 is relatively normal - FEV1/FVC normal

Question 30

Define Obstructive deficit, and give some features

Answer 30

Characterised by airway obstruction - If airways are narrowed, lungs can still fill to capacity - e.g. asthma, COPD

Question 31

What happens to FVC< FEV1 and FEV1/FVC when there is an obstructive deficit?

Answer 31

- FEV1 is reduced - FVC is normal - FEV1/FVC is reduced

Question 32

What is a vitalograph?

Answer 32

A lung function test that measures the ability to move air out of the lungs - FVC and FEV1

Question 33

What is Miller's prediction quadrant

Answer 33

It is used to predict the type of deficit, based on the FEV1 and FVC measurements

Question 34

What is peak expiratory flow rate? (PEF)

Answer 34

A measure of a person's maximum speed of expiration, as measured with a peak flow meter

Question 35

How is PEF measured + list some features of a flow-volume curve

Answer 35

The flow-volume curve consists of expiratory flow rate and expiratory volume - A patient takes a deep breath in (TLC measured) - Then they take a deep and fast breath out (RV is measured) - TLC is when lungs full, PEF is when highest rate of expiration, where flow falls and ceases at RV TLC to PEF: is effort dependen - increase in effort increases flow rate PEF to RV: is effort independent (vice versa)

Question 36

What is a flow-volume loop?

Answer 36

It is a flow-volume curve, that is done using the PEF rate method, but where the patient inspires again (loop)

Question 37

What does a large, wide, and tall loop show

Answer 37

Normal expiration - no deficit

Question 38

What does a smaller loop, starts at TLC, which is shifted to the left (larger RV), which has a change in the flow rate (it becomes less steep) show?

Answer 38

Obstructive deficit - patient is able to get to TLC - air can be moved from large airways, harder from small airways (compromised), giving the scoop effect (change in flow rate) - More air is also retained, which increases the RV, as smaller airways compromised, and retain the air

Question 39

What does a smaller loop, which does not start at TLC (lower TLC), ends at RV, and has the same flow rate of expiration show?

Answer 39

Restrictive Deficit - normal. shape, smaller, TLC reduced (less than 5L) - Airways normal - Issue is compliant - lungs cannot be filled as much as normal

Question 40

What is gas transfer - diffusion conductance?

Answer 40

It is a measure of how easily carbon monoxide crosses from the alveolar air to blood.

Question 41

How is the gas transfer test done? (diffusion conductance)

Answer 41

The test is done by: - Patient inhales a single breath of dilute carbon monoxide followed by a breath-hold of 10s - The diffusion capacity is calculated from lung volume and CO% in the alveoli in the beginning and end of the 10s breath-hold Clinical relevance - - e.g. in fibrosis of the lungs where gas diffusion is compromised