Respiratory measurements

Question 1

What is lung compliance?

Answer 1

Stretchiness of the lung - association between compliance and pressure

Question 2

How does lung compliance vary within the lungs and at exhalation and inhalation?

Answer 2

The base of the lungs are more stretchy than the apex
Inhalation: increase in compliance
Exhalation: elastic recoil

Question 3

What is high and low compliance associated with?

Answer 3

High compliance: low pressure, lung stretchier

Low compliance: high pressure, lung is stiffer

Question 4

What do we need for efficient ventilation? (2)

Answer 4

High lung compliance

Low alveolar surface tension due to surfactant

Question 5

What do tests for lung function need to include?

Answer 5

Mechanical condition of the lungs (pulmonary fibrosis)
Resistance of the airways (asthma)
Diffusion across the alveolar membrane (pulmonary fibrosis)

Question 6

What piece of apparatus can be used for lung volume and what does it measure? (4)

Answer 6

Bell spirometer

• Tidal volume
• Inspiratory reserved volume
• Expiratory reserved volume
• Vital capacity

Question 7

What are the 3 things a spirometer can’t measure?

Answer 7

Total lung capacity
Residual volume
Functional residual capacity

Question 8

What is the definition of tidal volume?

Answer 8

Volume of air entering and leaving the lung with each normal breath

Question 9

What is the definition of inspiratory reserved volume?

Answer 9

Extra volume of air inspired above the normal tidal volume with full force

Question 10

What is the definition of expiratory reserved volume?

Answer 10

Extra volume of air expired by forceful expiration at the end of the normal tidal expiration

Question 11

What is the definition of vital capacity?

Answer 11

Maximum amount of air expelled from the lungs after first filling the lungs to a maxim then expiring to a maximum (TV+IRV+ERV)

Question 12

What is FEV1.0 and its relationship with FVC?

Answer 12

Volume expired in the first second

Ratio- FEV1.0 : FVC

Question 13

What causes lung volume to decrease? (4)

Answer 13

Oedema
Emphysema
Smoking
altitude

Question 14

How do we measure functional residual capacity and what is its equation?

Answer 14

Spirometer with helium dilation or nitrogen washout - closed system

V1 x (C1-C2)/C2 = V2 (FRC)

Question 15

How does the nitrogen washout lung function test work? (4)

Answer 15

1. Patient inspires 100% O2
2. Expires into the spirometer system
3. Procedure repeated until N2 in lungs is replaced with O2
4. FRC calculated from exhaled N2 and estimated alveolar N2

Question 16

What is a restrictive deficit? (4)

Answer 16

• Lung expansion is compromised - alterations in lung parenchyma, disease of the pleura or chest wall
• Lungs don’t full to capacity
• Pulmonary fibrosis and scoliosis
• FVC reduced, FEV1 normal FEV1/FVC increased/normal

Question 17

What is an obstructive deficit? (4)

Answer 17

• Airways obstructed, narrowed, still fill capacity
• Resistance is increased on expiration
• Asthma, COPD
• FVC normal, FEV1 reduced. Low FEV1/FVC

Question 18

What is the graphical effect of restrictive and obstructive deficits? (3)

Answer 18

• Normal: Standard curve
• Obstructive: more linear curve, reaches plateau slower
• Restrictive: small curve which tails straight, doesn’t reach plateau

Question 19

What is a flow-volume loop?

Answer 19

Determines how much of the lung is filled and what air is left in the lungs

Question 20

What is a peak flow meter?

Answer 20

Small device to blow into and gives a reading

Question 21

How can gas transfer be measured? (3)

Answer 21

1. patient inhales a single breath of diluted CO then holds breath for 10secs
2. The diffusion capacity is calculated from the lung volume and the % of CO in the alveoli at the beginning and the end of the 10s hold
3. Clinical relevance - fibrosis of the lungs where gas diffusion is compromised