Respiratory Mechanics

Question 1

What are the 2 meanings of “respiration”?

Answer 1

Tissue respiration: the aerobic metabolism in cells

Breathing: gas exchange and the associated processes

Question 2

What does ‘respiratory mechanics’ refer to?

Answer 2

• The study of the mechanical properties of the lung and the chest wall
• The process by which air enters and leaves the lungs

Question 3

What do the lungs do (broadly)?

Answer 3

• Bring in fresh air rich in oxygen needed to fuel the body, and
• Expel waste gas (CO2) produced from cells in the body

Question 4

The movement of air into and out of the lungs is coupled to what?

Answer 4

Cellular respiration

Question 5

Death from lung disease is usually due to what?

Answer 5

Inability to overcome changes in lung and/or chest mechanics

Question 6

What is the typical value of PO2 at rest?

Answer 6

100 ± 2 mmHg

Question 7

What is the typical value of PCO2 at rest?

Answer 7

40 ± 2 mmHg

Question 8

What is the exchange of O2 and CO2 at rest?

Answer 8

~250ml O2/min, ~200ml CO2/min

Question 9

What is the exchange of O2 and CO2 when walking slowly (~3mph)?

Answer 9

~800ml O2/min, ~750ml CO2/min

Question 10

What is the exchange of O2 and CO2 during severe exercise?

Answer 10

~5000ml O2/min, ~6000ml CO2/min

Question 11

What is the function of the alveoli?

Answer 11

Act as sites of gas exchange between air and blood

Question 12

What is the role of the upper airways?

Answer 12

Conduct air to lung

Major functions: humidify air (saturate with water), warm air (to body temperature), filter air

Question 13

How do the upper airways filter air?

Answer 13

Upper airways to bronchioles lined by pseudo-stratified, ciliated columnar epithelium
Inhaled particles stick to mucus. Mucus moves towards mouth by beating cilia

Question 14

What volume of air is moved into the lungs at rest?

Answer 14

~6L/min

Question 15

What volume of air is moved into the lungs during severe exercise (max ventilation)?

Answer 15

~160L/min

Question 16

What is cardiac output value at rest?

Answer 16

5L/min

Question 17

What is the max cardiac output?

Answer 17

25L/min

Question 18

During quiet breathing, which process is active/passive?

Answer 18

Inspiration is active

Expiration is passive

Question 19

During quiet breathing, which process is active/passive?

Answer 19

Both inspiration and expiration are active

Question 20

Describe the active process of inspiration during quiet breathing

Answer 20

Diaphragm contracts downwards pushing abdominal contents outwards
External intercostals pull ribs outwards and upwards

Question 21

Describe the passive process of expiration during quiet breathing

Answer 21

Elastic recoil of the lungs and chest wall

Question 22

Describe the active process of inspiration during strenuous breathing

Answer 22

Greater contraction of the diaphragm and external intercostals
Inspiratory accessory muscles active e.g. sternocleidomastoid, alae nasi, pectoralis major muscles, etc.

Question 23

Describe the active process of expiration during strenuous breathing

Answer 23

Abdominal muscles (rectus abdominus, internal oblique, external oblique and transverse abdominus)
Internal intercostal muscles appose external intercostals by pushing ribs downwards and inwards

Question 24

What occurs during inspiration and expiration in terms of pressure?

Answer 24

Changes in pressure within the lung - intrapulmonary pressure

Question 25

What is the intrapleural pressure?

Answer 25

Pressure in the space between lung and chest wall | Pressure within this space is always negative

Question 26

What does 'tidal volume' refer to?

Answer 26

The volume of air that comes into the lung during each breath, typically 0.5L

Question 27

What is the pressure within the lung called?

Answer 27

Intrapulmonary pressure/alveolar pressure

Question 28

Why is the intrapleural pressure always negative?

Answer 28

Because the lung is always trying to pull inwards while the chest wall is always wanting to push outwards The 2 linings (parietal and visceral) are always trying to pull away from each other so the space between them is always negative

Question 29

At the beginning of inspiration, what is the value of PA (alveolar pressure i.e. pressure within the lungs)?

Answer 29

PA = 0 | Because there is no air flow

Question 30

Describe the pressure changes during inspiration

Answer 30

Beginning of inspiration, no flow -> PA (alveolar pressure) = 0 Inspiratiory muscles contract -> increase in thoracic volume Intrapleural pressure becomes more negative Increase in transpulmonary pressure Lungs expand and alveolar volume increases Alveolar pressure becomes negative (PA<0) Air moves into lungs from higher pressure to lower pressure Inspiration ends when PA = PB PB = barometric pressure

Question 31

What does transpulmonary pressure refer to?

Answer 31

The difference between alveolar pressure and the intrapleural pressure

Question 32

Describe the pressure changes during expiration

Answer 32

Beginning of expiration: thoracic volume decreases Intrapleural pressure and transpulmonary pressure return to pre-inspiration values Thorax and lungs recoil (elastic recoil pressure) Air in alveoli compressed Alveolar pressure becomes greater than barometric pressure Air flows out of lungs

Question 33

Describe low level breathing in a healthy individual

Answer 33

Low level breathing is very efficient: small muscle effort | 1ml of O2 for each litre of air breathed, 2% of resting energy expenditure

Question 34

What is the functional residual capacity (FRC)?

Answer 34

Functional residual capacity is the volume of air in the lung at the end of expiration during quiet breathing

Question 35

What effect do elastic recoil forces have on lung volume?

Answer 35

Decrease lung volume

Question 36

What effect does the outward recoil of chest all have on lung volume?

Answer 36

Increases lung volume

Question 37

At functional residual capacity, which forces are opposite and equal to one another?

Answer 37

Elastic recoil forces | Outward recoil forces

Question 38

When might FRC be decreased?

Answer 38

Functional residual capacity might be decreased when chest muscle walls are weak (neuromuscular disease) - elastic recoil is greater

Question 39

Even if an individual expires maximally, why does the lung not collapse?

Answer 39

Functional residual capacity within the lung | Residual volume maintained within lung at all time, keeps the alveoli open

Question 40

What can be used to measure lung volume?

Answer 40

Vitalograph/spirogram | Displays volume of gas exhaled against time

Question 41

What is FVC?

Answer 41

Forced vital capacity - total amount of air exhaled during the FEV test

Question 42

What is FEV1?

Answer 42

Forced expiratory volume in 1 second

Question 43

What is FEF25-75?

Answer 43

Average mid-maximal expiratory flow

Question 44

What is the FEV1/FVC ratio in a healthy individual?

Answer 44

>70% | i.e. >70% of lung volume expired in 1 second

Question 45

What is the FEV1/FVC ratio in patients with obstructive lung diseases?

Answer 45

<70% - less than 70% of lung volume expired in 1 second

Question 46

What is the FEV1/FVC ratio in patients with restrictive lung diseases?

Answer 46

>70% | Lung volume is smaller (FVC), usually 80% or less of healthy individual

Question 47

What are 2 examples of obstructive lung diseases?

Answer 47

Emphysema and asthma

Question 48

What are 2 examples of restrictive lung diseases?

Answer 48

Pulmonary fibrosis | Neuromuscular diseases