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BS - Respiratory System > Mechanics of Breathing 2 > Flashcards

Mechanics of Breathing 2 Flashcards

1
Q

What is functional residual capacity (FRC) and what is it dependent on?

A

It is the volume of air present in the lungs after passive expiration

It is dependent on the compliance of the lungs and chest wall

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2
Q

What happens at FRC?

A

The opposing elastic recoil forces of the lungs and chest wall are in equilibrium

There is no exertion by the diaphragm or other respiratory muscles

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3
Q

What is compliance?

A

The change in lung volume per unit change in intrathoracic pressure

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4
Q

What does compliance measure?

A

It is a measurement of the ability of the lungs and chest wall to stretch and expand

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5
Q

What are the 2 types of compliance?

A

static compliance and dynamic compliance

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6
Q

What is the equation for compliance?

A

C = change in volume/change in pressure

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7
Q

What is static compliance?

A

The change in volume for any given applied pressure when there is no air flow

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8
Q

What is static compliance a function of?

A

A function of elastic recoil of the lung and surface tension of the alveoli

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9
Q

What is dynamic compliance?

A

The compliance of the lung at any given time during the actual movement of air

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10
Q

Why is dynamic compliance always less than static compliance?

A

Dynamic compliance includes the pressure required to generate flow by overcoming resistance forces

There is always a degree of airway resistance

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11
Q

What is an oesophageal balloon used to measure?

A

Intrathoracic pressure

This is the pressure that is present between the 2 layers of pleura

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12
Q

What is the assumption made when measuring intrathoracic pressure?

A

It is measured indirectly by assuming that the pressure in the thorax and the pressure in the chest wall are equal, at the end of either inspiration or expiration

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13
Q

Why are the lungs both compliant and elastic?

A

They are elastic to recoil and push air out during expiration

They are compliant to fill with air during inspiration

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14
Q

At the start and end of expiration, what is alveolar pressure?

A

At the start and end of expiration, alveolar pressure is in equilibrium with atmospheric pressure

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15
Q

What is recoil pressure of the lung?

A

The pressure that drives the lung to collapse

The lung has a natural tendency to collapse on itself

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16
Q

How is recoil pressure determined?

A

Determined by the different between alveolar pressure and intrapleural pressure

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17
Q

At maximal expiration, what is alveolar pressure and why?

A

Breathing all the way out keeps the glottis open so alveolar pressure is zero

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18
Q

What is maximal intrapleural pressure and recoil pressure after maximal expiration?

A

Maximum intrapleural pressure is -3 cm of water

Recoil pressure is +3 cm of water

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19
Q

What is the equation for recoil pressure?

A

Alveolar pressure - intrapleural pressure

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20
Q

At maximal expiration, what lung volume is present?

A

+3 cm of water is at the residual volume

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21
Q

After expiration and during normal tidal breathing, what lung volume is present?

A

Functional residual capacity is the volume of air left in the lungs

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22
Q

After expiration and during normal tidal breathing, what is intrapleural pressure?

A

around -5 cm of water

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23
Q

After expiration and during normal tidal breathing, what is recoil pressure?

A

alveolar pressure is still 0 as the glottis is open so

0 - - 5 = +5

recoil pressure is +5 cm of water

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24
Q

At peak inspiration, what is the intrapleural pressure?

A

A very negative pressure is generated in the chest during maximal inspiration

intrapleural pressure is -30 cm of water

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25
What is recoil pressure at peak inspiration and what lung volume is this equivalent to?
+30 cm of water total lung capacity
26
Which 3 points are needed to draw a lung compliance curve?
1. residual volume 2. functional residual capacity 3. total lung capacity
27
When is compliance low and high and what does this mean?
It is low when the lung is expanded - a lot of effort is required to expand the alveoli more It is high after expiration meaning less effort is needed to expand the alveoli
28
Which pressures determine chest wall compliance?
Intrapleural pressure and barometric pressure
29
How is recoil pressure of the chest wall calculated?
intrapleural pressure - barometric pressure
30
What is the value of atmospheric pressure?
It is zero unless the altitude is altered
31
How do you remove the effect of the lung when measuring chest wall compliance?
Breathe all the way out, close the glottis and relax the muscles Closing the glottis prevents air from entering the lungs
32
After maximal expiration, what is the recoil pressure of the lungs?
minimum recoil pressure is generated after maximal expiration this is -30 cm of water and is residual volume
33
Once the glottis is open, what is the recoil pressure (&intrapleural pressure) of the chest wall?
-5 cm of water this is the functional residual capacity
34
During maximal inspiration, how is total lung capacity reached?
The glottis is closed and the muscles are relaxed The volume of air in the lung is retained by closing the g,lottis
35
What is recoil pressure of the chest wall at maximal inspiration?
The highest possible intrapleural pressure of +3 cm of water is reached Chest wall compliance is +3 cm of water
36
What does the overall effect of compliance take into account?
Both chest wall and lung compliance
37
What is the overall effect of compliance at maximal expiration?
the lungs are compliant the resistance to compliance caused by the chest wall overrides the stretchiness of the lungs
38
What is significant about functional residual capacity on the compliance curve?
It is a relaxation and equilibrium point The chest wall and lung recoil pressures are equal but opposite
39
Where does FRC appear on the compliance curve?
where the curve crosses the zero pressure point on the y axis
40
What is the problem with having a lower FRC?
Normal tidal breathing becomes closer to residual volume There is less expiratory reserve volume so if there is a need to increase ventilation, the capacity to increase the volume of ventilation is diminished
41
During tidal breathing, why is there a difference between compliance during inspiration and expiration?
It is not caused by a difference in compliance as the lung elasticity is the same It is caused by changes in the calibre of the airways
42
Why does hysteresis occur?
the elastic nature of the tissues and airway resistance
43
What is hysteresis?
any process where the future state of a system is dependent on its current and previous state it means that the compliance of the lung is different in inspiration and expiration
44
What is the difference in lung volumes during inspiration and expiration?
Lung volume at any given pressure during inspiration is less than the lung volume at the same pressure during expiration
45
Why does hysteresis occur in dynamic compliance curves?
It occurs due to airway resistance, which is a function of flow rate
46
In a dynamic compliance curve, when is flow rate maximal?
flow rate (and resistance) is maximal at the beginning of inspiration and the end of expiration
47
Why does hysteresis occur in a static compliance curve?
There is no resistive component Hysteresis occurs due to viscous resistance of surfactant and the lungs
48
how is a heavy smoker defined?
someone who smokes at least 1 cigarette each day
49
What happens in pulmonary fibrosis?
elastic tissue becomes replaced with fibrous scar tissue this causes lung tissue to become thickened and stiff
50
Where does scarring normally occur in pulmonary fibrosis?
A network of tissue called the interstitium, which surrounds the alveoli
51
What is the effect of scar tissue developing in pulmonary fibrosis?
Scar tissue is not elastic Lungs lose their ability to transfer oxygen into the bloodstream as they cannot take in as much oxygen from the air during inspiration
52
what are the main symptoms of pulmonary fibrosis?
Breathing requires more effort so patients are breathless just from walking a persistent cough feeling tired all the time
53
what are the main causes of pulmonary fibrosis?
1. being exposed to certain types of dust including wood, metal dust or asbestos 2. being exposed to allergens 3. side effect of a drug 4. for most cases, a specific cause cannot be found
54
What is kyphoscoliosis? What is it caused by?
caused by a decrease in chest wall compliance restrictive lung disease that causes extrapulmonary restriction of the lungs
55
What do the terms "kyphosis" and "scoliosis" describe?
Kyphosis - anterior-posterior curvature of the spine Scoliosis - lateral displacement of the spine
56
What is the effects of kyphoscoliosis?
restriction of the lungs leads to an impairment of pulmonary functions and respiratory failure the ribs cannot articulate properly with the spinal column
57
What is the main cause of kyphoscoliosis?
80% of cases are idiopathic - the cause is unknown
58
What is a circumferential burn?
a burn that goes all the way around the body
59
what happens to the tissue after a circumferential burn?
the tissue becomes burnt and forms scar tissue this is not elastic and restricts the expansion of the chest
60
What is the effect of a circumferential burn?
reduced chest wall compliance which hinders ventilation
61
How is scar tissue removed in a circumferential burn?
a surgical method called an escharotomy
62
what occurs in emphysema?
the alveolar membranes are destroyed causing the alveoli to fuse together this means there is less lung tissue
63
How does emphysema affect gas exchange?
surface area of the alveoli are reduced so the volume of oxygen diffusing into the blood is also reduced
64
how does emphysema affect compliance of the lung?
elasticity and compliance are increased
65
Why is compliance in different parts of the lung not the same?
due to the effect of gravity
66
Why is compliance greatest at the base of the lung?
the same pressure is applied to every part of the lung as intrapleural pressure is the same the bottom of the lung has a greater increase in volume as ventilation is greater at the bottom
67
What is closing capacity of the lung?
It is the point during expiration when small airways begin to close it increases with age and decreased pulmonary blood flow
68
What affect does age have on the alveoli?
as you get older, some of the alveoli become closed during expiration closed alveoli have low compliance
69
What happens if closing capacity exceeds FRC?
Alveoli in dependent parts of the lung are poorly ventilated They will be closed or collapsed during normal tidal breathing
70
What is the problem with increased closing capacity?
It decreases the compliance of the lung
71
What would happen to the alveoli if there was no surfactant and why?
The alveoli are interconnected by bronchioles so all of the air would empty into the larger alveolus All the alveoli are different sizes
72
What is the Law of Laplace?
P = 2t/r ``` P = pressure t = surface tension r = radius of alveolus ```
73
What does the Law of Laplace state?
The pressure needed to be applied to a sphere to prevent it from collapsing is inversely proportional to the radius
74
What is the role of surface tension?
Surface tension opposes pressure and acts inwards to create a collapsing force A greater surface tension leads to a greater collapsing motion
75
What is the role of surfactant?
There is a tendency for smaller alveoli to collapse and empty into larger alveoli This motion is overcome by altering the surface tension within the alveolus by producing surfactant
76
What cells produce surfactant?
specialised alveolar epithelial cells called type II cells
77
What is surfactant made from?
It comprises 90% phospholipid and 10% protein
78
Which disease shows a deficiency in surfactant? What happens?
infant respiratory distress syndrome collapsing pressure is not equalised so the smaller airways collapse
79
What are the 3 roles of surfactant?
1. increases pulmonary compliance 2. prevents atelectasis 3. aids alveolar recruitment and minimises alveolar fluid
80
What happens in atelectasis?
there is collapse or closure of a lung resulting in reduced or absent gas exchange the alveoli are deflated down to no or little volume
81
How does surfactant prevent alveolar collapse in alveoli of different sizes?
each alveolus produces the same amount of surfactant the surfactant becomes more dispersed as alveolar volume increases it equalises pressure between alveoli of different sizes
82
In which size alveoli does surfactant have the greatest effect on reducing surface tension?
smaller alveoli in larger alveoli, the surfactant is more dispersed around the inner wall
83
How is the potential energy of the lungs generated?
the energy used to overcome elastic forces in inspiration is stored as potential energy potential energy is dissipated in expiration
84
How is work expended during breathing?
Work is expended in the form of heat to overcome resistance forces of air passing through the airways
85
How is the work of breathing calculated?
work = volume x pressure
86
What is airway resistance?
The opposition to the flow os air caused by forces of friction
87
What is the resistance to flow like in laminar flow?
resistance is quite low only a small driving pressure is required to produce a certain flow rate
88
What is the resistance to flow like in turbulent flow?
resistance is much larger a much larger driving pressure is required to produce the same flow rate
89
What factors increase resistance to air flow?
reducing the radius of the airway when the airways begin to branch
90
What % of energy expenditure is taken up by breathing in a healthy person?
2 - 5 %
91
At maximal hyperventilation, what % of energy expenditure is taken up by breathing?
30%
92
how is the work of breathing minimised in restrictive and obstructive lung conditions?
restrictive - taking rapid shallow breaths obstructive - taking large volume, slow breaths

BS - Respiratory System (20 decks)

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