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BDS1 BAMS: Respiratory System > Respiratory Mechanics > Flashcards

Respiratory Mechanics Flashcards

1
Q

What are the 2 meanings of “respiration”?

A

Tissue respiration: the aerobic metabolism in cells

Breathing: gas exchange and the associated processes

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2
Q

What does ‘respiratory mechanics’ refer to?

A
  • The study of the mechanical properties of the lung and the chest wall
  • The process by which air enters and leaves the lungs
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3
Q

What do the lungs do (broadly)?

A
  • Bring in fresh air rich in oxygen needed to fuel the body, and
  • Expel waste gas (CO2) produced from cells in the body
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4
Q

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

A

Cellular respiration

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5
Q

Death from lung disease is usually due to what?

A

Inability to overcome changes in lung and/or chest mechanics

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6
Q

What is the typical value of PO2 at rest?

A

100 ± 2 mmHg

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7
Q

What is the typical value of PCO2 at rest?

A

40 ± 2 mmHg

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8
Q

What is the exchange of O2 and CO2 at rest?

A

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

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9
Q

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

A

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

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10
Q

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

A

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

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11
Q

What is the function of the alveoli?

A

Act as sites of gas exchange between air and blood

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12
Q

What is the role of the upper airways?

A

Conduct air to lung

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

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13
Q

How do the upper airways filter air?

A

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

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14
Q

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

A

~6L/min

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15
Q

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

A

~160L/min

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16
Q

What is cardiac output value at rest?

A

5L/min

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17
Q

What is the max cardiac output?

A

25L/min

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18
Q

During quiet breathing, which process is active/passive?

A

Inspiration is active

Expiration is passive

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19
Q

During quiet breathing, which process is active/passive?

A

Both inspiration and expiration are active

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20
Q

Describe the active process of inspiration during quiet breathing

A

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

21
Q

Describe the passive process of expiration during quiet breathing

A

Elastic recoil of the lungs and chest wall

22
Q

Describe the active process of inspiration during strenuous breathing

A

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

23
Q

Describe the active process of expiration during strenuous breathing

A 
Abdominal muscles (rectus abdominus, internal oblique, external oblique and transverse abdominus)
Internal intercostal muscles appose external intercostals by pushing ribs downwards and inwards
24
Q

What occurs during inspiration and expiration in terms of pressure?

A

Changes in pressure within the lung - intrapulmonary pressure

25
Q

What is the intrapleural pressure?

A

Pressure in the space between lung and chest wall

Pressure within this space is always negative

26
Q

What does ‘tidal volume’ refer to?

A

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

27
Q

What is the pressure within the lung called?

A

Intrapulmonary pressure/alveolar pressure

28
Q

Why is the intrapleural pressure always negative?

A

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

29
Q

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

A

PA = 0

Because there is no air flow

30
Q

Describe the pressure changes during inspiration

A

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

31
Q

What does transpulmonary pressure refer to?

A

The difference between alveolar pressure and the intrapleural pressure

32
Q

Describe the pressure changes during expiration

A

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

33
Q

Describe low level breathing in a healthy individual

A

Low level breathing is very efficient: small muscle effort

1ml of O2 for each litre of air breathed, 2% of resting energy expenditure

34
Q

What is the functional residual capacity (FRC)?

A

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

35
Q

What effect do elastic recoil forces have on lung volume?

A

Decrease lung volume

36
Q

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

A

Increases lung volume

37
Q

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

A

Elastic recoil forces

Outward recoil forces

38
Q

When might FRC be decreased?

A

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

39
Q

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

A

Functional residual capacity within the lung

Residual volume maintained within lung at all time, keeps the alveoli open

40
Q

What can be used to measure lung volume?

A

Vitalograph/spirogram

Displays volume of gas exhaled against time

41
Q

What is FVC?

A

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

42
Q

What is FEV1?

A

Forced expiratory volume in 1 second

43
Q

What is FEF25-75?

A

Average mid-maximal expiratory flow

44
Q

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

A

> 70%

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

45
Q

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

A

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

46
Q

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

A

> 70%

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

47
Q

What are 2 examples of obstructive lung diseases?

A

Emphysema and asthma

48
Q

What are 2 examples of restrictive lung diseases?

A

Pulmonary fibrosis

Neuromuscular diseases

BDS1 BAMS: Respiratory System (8 decks)

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