Physiology ✅ Flashcards
1
Q
What must be overcome for air to flow?
A
Airway resistance
2
Q
What is airway resistance the result of?
A
Frictional force which opposes the flow of air
3
Q
Of what type of flow is most airflow in airways under normal conditions?
A
Laminar
4
Q
What equation determines the resistance for laminar flow?
A
Poiseuille’s equation:
Resistance = (8 x length x viscosity of gas) / (π x (radius)^4)
5
Q
What does Poiseuille’s equation predict?
A
That resistance increases dramatically as diameter decreases
6
Q
What structures produce most resistance to airflow?
A
Trachea and larger bronchi
7
Q
Why do the trachea and larger bronchi produce the most resistance to airflow?
A
Because the branching of the tracheobronchial tree, the combined cross-sectional area is sufficiently large enough to provide little resistance to flow
8
Q
What is the cross sectional area of the trachea compared to the total cross sectional area at the 23rd branching?
A
3cm^2 at trachea, 4m^2 at 23rd branching
9
Q
Why do young children have an increased resistance to airflow?
A
Smaller size of airways
10
Q
Why can the chest wall of young children become drawn inwards with each breath in young children, even in health?
A
- Increased resistance to airflow
- Reduction in chest wall compliance
11
Q
When might the chest wall being drawn inwards with each breath get worse?
A
If there are any additional factors that increase airway resistance, e.g. bronchiolitis
12
Q
What is the compliance of the lung a measure of?
A
How easily it can be distended
13
Q
What formula calculates lung resistance?
A
Change in volume / change in pressure
14
Q
What is required to generate airflow during the first part of inspiration?
A
A relatively greater pressure
15
Q
What does compliance vary depending on?
A
The exact lung volume
16
Q
How does compliance vary with age?
A
A newborn child has very low compliance compared to a young adult
17
Q
What is the typical lung compliance of an adult male?
A
0.09 - 0.26 L/cmH2O
18
Q
What is the typical lung compliance for a newborn infant?
A
0.0005 L/cmH2O
19
Q
What is the primary control of breathing via?
A
The autonomic nervous system
20
Q
What stimuli can increase the rate of breathing?
A
- Emotional stimuli
- Peripheral chemoreceptors
- Central chemoreceptors
- Receptors in muscles and joints
- Receptors for touch, temperature, and pain stimuli
- Cerebral cortex
21
Q
What stimuli can reduce the rate of breathing?
A
- Emotional stimuli
- Stretch receptors in the lungs
- Cerebral cortex
22
Q
Through what system can emotional stimuli change the rate of breathing?
A
Limbic systemic
23
Q
What changes detected by peripheral chemoreceptors may trigger an increased rate of breathing?
A
- Decreased oxygen
- Increased CO2
- Increased hydrogen
24
Q
What changes detected by central chemoreceptors may trigger an increased rate of breathing?
A
- Increased CO2
- Increased hydrogen
25
Where are the respiratory centres located?
In the medulla and pons
26
What co-ordinates voluntary control over breathing?
Cerebral cortex
27
Where is control of breathing mediated?
Mainly (but not exclusively) through neural centres in the brainstem
28
What is responsible for the rapid respiratory response to changes in arterial carbon dioxide?
Carbon dioxide in the blood diffuses rapidly into the CSF, where it reacts with water to release hydrogen ions
29
Where are peripheral chemoreceptors located?
In the carotid and aortic bodies
30
What are peripheral chemoreceptors sensitive to?
Oxygen and carbon dioxide
31
Where are irritant receptors located?
In the upper and lower airways
32
Where are mechanical receptors located?
In the lungs and chest wall
33
What do the peripheral chemoreceptors, irritant receptors, and mechanical receptors facilitate?
The response to hypoxia
34
How does the speed of response to hypoxia compare to that of hypercapnia?
It is much less rapid
35
Why does metabolic acidosis tend to be incompletely and slowly corrected?
As excess H+ will only cross the blood-brain barrier slowly
36
How can autonomic control of breathing be overridden?
Conscious control enabling, e.g. speech and breath holding
37
Where are voluntary conscious signals for breathing generated?
In the cortex
38
How are voluntary conscious signals for breathing conducted to the muscles of breathing?
Via the corticospinal tract
39
What is normal, quiet breathing termed?
Tidal
40
What is the rate and depth of quiet breathing controlled by?
The brainstem
41
What determines the distribution of air within the lungs during tidal breathing?
The regional variation in airway resistance and lung compliance
42
What happens to the volumes of the lungs in an upright child?
There is relative over-distention of the apices and relatively reduced volume at the bases
43
Why is their relative over-distention of the apices and reduced volume at the bases in an upright child?
Because the wright of the lungs ensures that the pleural pressure is more negative at the apex
44
At what age is the relative over-distention at the apices and reduced volume at bases in an upright child most prominent?
Infants and early childhood
45
Why is the relative over-distention at the apices and reduced volume at the bases in an upright child most prominent in infants and early childhood?
It is opposed by the rigid chest wall and stronger respiratory muscles in adult life
46
What is an increase in airway resistance usually due to in an infant?
Airway narrowing, e.g. smooth muscle thickening and/or airway cell oedema
47
What will any increase in airway resistance in an infant lead to?
Greater effort of breathing
48
What signs of respiratory distress may be found in infants?
- Abdominal breathing
| - Sternal/intercostal recession
49
Why do infants in respiratory distress have abdominal breathing and sternal/intercostal recession?
The relatively weak intercostal muscles and non-compliant chest wall are unable to oppose the stronger contraction of the diaphragm
50
What is the major muscle of respiration?
The diaphragm
51
How does the muscle fibre content of the diaphragm differ in at birth compared to in adulthood?
At birth, fatigue-resistant striated muscle fibres account for only 10% of its muscle mass, which increases to 50% by early adulthood
52
What is the result of the diaphragm having. lower content of fatigue-resistant striated muscle at birth?
Infants will tire more quickly, and are at increased risk of apnoea and respiratory failure if their work of breathing needs to increase for more than a few minutes for any reasons
53
Give 2 reasons why work of breathing may increase in an infant?
- Bronchiolitis
| - Heart failure due to VSD
54
What does the less compliant chest wall of an infant predispose the airway too?
Predisposes the immature airway to partial closure, particularly at the lung bases
55
What does the partial closure of the airways due to reduced compliance in an infant lead to?
Intrapulmonary shunting of blood through non-ventilated areas
56
What happens to diaphragm function during sleep?
It is largely preserved
57
Why is diaphragm function during sleep preserved?
Because it is essential for maintenance of adequate ventilation
58
What happens to accessory muscle function during sleep?
It is reduced, particularly during REM sleep
59
What is the result of accessory muscle function being reduced during sleep?
This may contribute to hypoventilation and ventilation-perfusion mismatching, resulting in oxygen desaturation
60
Why shouldn't you place a child in respiratory distress in a horizontal position?
It can lead to ventilation perfusion mismatch
61
Where does the matching of ventilation with perfusion take place?
Within the airways and alveoli
62
Why might placing a child in respiratory distress lead to ventilation-perfusion mismatch?
Placing a child with respiratory distress in a horizontal position leads to an immediate reduction of ventilation in the dependent lungs. Sudden changes cannot be instantly compensated for, and so the change in ventilation is not immediately accompanied by a change in lung perfusion, causing mismatch and potentially decreasing sats
63
What is minute volume?
The volume of inspired air and expired gases that move in and out of the lungs each minute
64
What is the minute volume a product of in normal breathing?
Tidal volume and respiratory rate
65
What is tidal volume?
The volume of each breath
66
What does spirometry measure?
Lung volume changes
67
From what age can spirometry be used?
5
68
What values can be measured using a spirometer?
- Vital capacity
| - FEV1
69
What values require different techniques to measure?
- Total lung capacity
- Functional residual capacity
- Residual volume
70
What is exchange of gas across a surface dependent on?
- The gradient of partial pressure across it
- The surface area
- The magnitude of the diffusion distance
71
How does gas transfer occur?
By diffusion
72
Is carbon dioxide water soluble?
Yes, very
73
What is the result of carbon dioxide being very water soluble?
It diffuses much more readily than oxygen, and is less affected bye increases in diffusion distance
74
Give an example of when there might be an increase in diffusion distance in the lungs?
Pulmonary oedema
75
What do the differential changes seen in blood carbon dioxide and oxygen content in respiratory failure allow us to understand?
Where the problem is occurring
76
What happens when there is an increase in FiO2 in alveolar hypoventilation?
Correction of hypoxia
77
What happens to arterial CO2 in alveolar hypoventilation?
Increased
78
What happens when there is an increase in FiO2 in impaired diffusion?
Correction of hypoxia
79
What happens to arterial CO2 in alveolar hypoventilation?
Normal or decreased
80
What happens when there is an increase in right-left shunt or ventilation-perfusion imbalance?
Little change or no change
81
What happens to arterial CO2 in right-left shunt or ventilation-perfusion imbalance?
Decreased
82
How much oxygen is dissolved in plasma?
3ml/L of arterial blood
83
How is the vast majority of oxygen transported?
Bound to haemoglobin
84
What does oxygen saturation describe?
The amount of haemoglobin molecules that are bound to oxygen
85
What is meant by 100% saturations?
All the possible sites for oxygen binding within haemoglobin are occupied
86
What shows the relationship between oxygen saturation and oxygen content of blood?
The oxygen dissociation curve
87
Which type of Hb has the steepest oxygen dissociation curve?
Fetal Hb
88
At what kPa (partial pressure of oxygen) does adult Hb unload most of its oxygen?
2.5-6.5kPa
89
At what kPa does fetal Hb unload most of its oxygen?
1.3-5.2kPa (so tissue has to be lower in oxygen for fetal Hb to give it up)
90
Why does fetal Hb unload most of its oxygen at a lower kPa?
Because fetal Hb does not bind 2,3-DPG efficiently, and thus will tend to 'hold on' to oxygen at the expensive of maternal Hb during pregnancy
91
Why is both fetal and adult Hb able to unload its oxygen?
Because the tissue store for oxygen is myoglobin, whose dissociation curve is even further to the left (meaning it binds oxygen more strongly)
92
What happens if Hb binds oxygen more strongly?
The dissociation curve is shifted to the left, and oxygen is less readily delivered to the tissues
93
What alters the oxygen dissociation curve?
- The presence of hydrogen ions (the Bohr effect)
- 2,3-DPG
- Carbon dioxide
94
What happens to the oxygen dissociation curve when there is an increase in hydrogen irons, 2,3-DPG, or CO2?
It is shifted to the right
95
What is the result of the oxygen dissociation curve being shifted to the right?
Less oxygen remains bound to Hb molecule at the same partial pressure of oxygen
96
What is the result of the oxygen dissociation curve being shifted to the right in the presence of hydrogen ions or CO2?
Oxygen tends to be better delivered to areas with higher concentrations of hydrogen ions and carbon dioxide
97
Why is newly transfused blood less efficient at delivering oxygen?
It is low in 2,3-DPG
98
What is meant by total lung capacity?
The maximum amount of air the lungs can accommodate
99
What is meant by tidal volume?
The amount of air inspired and expired at each breath
100
What is the usual tidal volume?
6-8ml/kg
101
What is meant by expiratory reserve volume?
The amount of air that can be exhaled after normal, quiet expiration
102
What is meant by residual volume?
The amount of air that remains in the lungs after the end of maximal voluntary expiration
103
What is meant by inspiratory reserve volume?
The amount of air that can be inhaled at the end of normal tidal inspiration
104
What is meant by vital capacity?
The sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume
