Respiratory Physiology Flashcards
1
Q
How is airflow through the airway calculated
A
Alveolar pressure - (atmospheric pressure / Resistance)
2
Q
Function of airway cilia
A
To transport mucus from the airways to the pharynx where it is swallowed
3
Q
What is the water vapour within the airways at 37 degrees
A
6.3kPa
4
Q
What is the intrapleural pressure at the beginning of inspiration
A
-4cmH2O
5
Q
What is the peak intrapleural pressure on inspiration
A
- 9cmH20 during normal breathing
- 30cmH2O during exercise
6
Q
What type of process is exhalation
A
Passive process from recoil of the chest wall
7
Q
List the 3 forces acting on the lung
A
- Elastic nature of lungs = inward pull on visceral pleura
- Surfactant = inward pressure
- Negative intrapleural pressure = outward pull
8
Q
What is Hysteresis
A
Unequal pressure required to maintain a given lung volume on inspiration and expiration
9
Q
Where is surfactant produced
A
Type 2 alveolar cells
10
Q
Describe surface tension
A
- Occurs at all air-fluid interfaces
- Water molecules are more attached to each other than the surrounding gas molecules
- Creates an inward pressure
11
Q
Biggest contributor to the elastic recoil of the lungs
A
Surface tension
12
Q
What is the primary purpose of surfactant
A
Reduce surface tension at the pulmonary air-liquid interface to reduce work of breathing
13
Q
Define the Law of Laplace
A
Alveolar distending pressure is proportional to surface tension / radius
14
Q
What does the Law of Laplace imply
A
As alveoli decrease in size the pressure within them would increase and result in collapse (if surfactant were not present)
15
Q
What is the relationship between alveolar radius and surfactant production
A
They increase or decrease in tandem
16
Q
Describe lung compliance
A
- The ease at which the lungs can be inflated
- Compliance = change in volume / change in pressure
17
Q
What two factors govern lung compliance
A
- Elasticity of the lung parenchyma
2. Surface tension
18
Q
List conditions that increase lung compliance
A
Emphysema
19
Q
List conditions that reduce lung compliance
A
- Scarring/fibrosis
- Pulmonary oedema
- Deficiency of surfactant e.g. prematurity
- Decreased lung expansion e.g. paralysis
- Supine position
- Mechanical ventilation (due to reduced pulmonary blood flow)
- Age
- Breathing 100% O2
20
Q
What class as non-elastic forces of chest wall movement
A
- Airway resistance
- Frictional forces
- Inertia of the air and tissues
21
Q
How is airway resistance divided throughout the respiratory tract
A
- 1/3rd = upper airways
- 2/3rd = tracheobronchial tree (primarily the medium-sized bronchi)
22
Q
Relationship between resistance and lung volume
A
Resistance falls as lung volumes increase as the elastic parenchyma pulls open the bronchioles
23
Q
Describe the 4 phases of lung expansion
A
- Takes considerable pressure increase before there is change in volume
- Expansion of the lung is proportional to the increase in pressure
- Maximum capacity
- In the initial stage the lung volume is maintained until the pressure falls considerably
24
Q
Shape of the lung inflation (compliance) curve
A
Sigmoid
25
How does tension pneumothorax develop
Lung injury forms a valve in which air leaks into the pleural cavity but closes during expiration leading to positive intrapleural pressure
26
When does a sucking pneumothorax develop
If defect in the chest wall is greater than 2/3rd the diameter of the trachea then air will enter via the chest wall as oppose to traditional airway
27
Define tidal volume
Air taken in and exhaled during quiet breathing
28
Define inspiratory reserve volume
Maximum volume of air that can be inspired in excess of normal inspiration
29
Define expiratory reserve volume q
Maximum volume of air that can be expired forcefully after normal expiration
30
Define functional residual capacity
Volume of gas left in the lungs. after expiration during normal breathing
31
How is functional residual capacity calculated
Using Helium dilution method
32
Define residual volume
Volume of air remaining after maximal expiration (FRC - ERV)
33
Define vital capacity
Volume of air that is expelled from maximal inspiration to maximal expiration
34
Define anatomical deadspace
Volume of gas that does mix with air in the alveoli
35
Define physiological deadspace
Volume of gas that may reach air in the alveoli but due to lack of perfusion does not take part in gas exchange (includes anatomical deadspace)
36
How is anatomical deadspace calculated
Fowler's method - uses nitrogen analyser
37
How is physiological deadspace calulated
Bohr equation - based on principle that all expired CO2 comes from the alveoli
38
What factors increase anatomical dead space
- Increasing size of patient
- Standing position
- Increased lung volume
- Bronchodilatation
- Ventilation
39
Factors increasing physiological deadspace
- Hypotension
- Hypoventilation
- Emphysema and PE
- Positive pressure ventilation
40
Define closing capacity
The volume of the lungs at which small airways at the base of the lungs start to close (usually 10% of vital capacity)
41
What factors increase closing capacity
- Increasing age
- Supine posture
- Anaesthesia
42
How is diffusion capacity measured
1. Inhalation of CO
| 2. Measurement of arterial CO
43
What reduces diffusion capacity
- Increase in diffusion distance e.g. pulmonary oedema
| - Loss of alveolar surface area e.g. emphysema
44
Describe hypoxic pulmonary vasoconstriction
Hypoxia or hypercapnia result in constriction of the small alveolar vessels to divert blood to better oxygenated areas of the lung
45
What is the typical pulmonary artery pressure
25/8mmHg
46
What 3 factors determine pulmonary blood flow
- Hydrostatic pressure in the pulmonary arteries
- Pressure in the pulmonary veins
- Pressure of air in the alveoli
47
Where in the lung is pulmonary blood flow the worst
Apex of the lung - alveolar pressure is similar to PA pressure causing small vessels to be compressed
48
What happens to pulmonary resistance when Cardiac output increases and why
Reduces:
- Distension of already open vessels
- Recruitment of additional vessels
49
What does V/Q equal in alveoli that are ventilated but not perfused
Infinity
50
What does V/Q equal in alveoli that are not ventilated but well perfused
0
51
Where is the ideal V/Q of 1 found in the lung
Approximately 2/3rd the way up the chest
52
List the causes of PE
- DVT
- Fat embolism
- Amniotic fluid embolism
- Air embolism
- Tumour fragments
53
List the physiological changes associated with PE
- Increased pulmonary vascular resistance
- Pulmonary HTN
- Increased RV afterload
- Reduced LV output
- Impaired gas exchange
- Decreased lung compliance from reduced surfactant
54
Normal volume of fluid in the lung interstitium
20-30ml
55
List the three stages of pulmonary oedema
1. Interstitial oedema
2. Alveolar oedema
3. Airway oedema
56
List the physiological effects of pulmonary oedema
- Decreased lung compliance
| - Increased airway resistance
57
What are the 2 phases of ARDS
1. Acute exudative
| 2. Late organisation
58
What forms during the acute exudative phase of ARDS
Hyaline membranes
59
What occurs in the organisation phase of ARDS
1. Regeneration of type 2 pneumocytes
| 2. Hyaline membranes organise with pulmonary fibrosis
60
What 3 factors affect the diffusion of gasses in the lungs and peripheral tissues
1. Pressure gradient
2. Diffusion coefficient
3. Tissue factors
61
What does oxygen have to cross to reach the circulation in the lungs
1. Pulmonary surfactant
2. Alveolar epithelium
3. Alveolar epithelium basement membrane
4. Pulmonary capillary endothelium
62
How does alveolar air composition differ from room air composition
Addition of water vapour and constant removal of O2
63
Define shunting
Passage of blood through the lungs without coming into contact with ventilated alveoli
64
Causes of shunting
- Pneumonia
- ASD
- VSD
- PDA
65
Describe the structure of Hb
- Consists of 4 peptide chains = 2 alpha and 2 beta chains
- Each chain has a haem group
- Haem group = protoporphyrin ring surrounding ferrous (Fe2+) molecule
66
How much oxygen can each gram of Hb carry
1.34ml
67
What does the oxygen dissociation curve illustrate
Relationship between the partial pressure of O2 and the concentration of O2 in the blood
68
What does a right shift of the oxygen dissociation curve demonstrate
Reduced affinity for oxygen of haemoglobin and thus oxygen will be released at a higher pO2 (Bohr Effect)
69
What does a left shift of the oxygen dissociation curve demonstrate
Increased affinity for oxygen of haemoglobin
70
List the causes of a left shift of the oxygen dissociation curve
- Alkalosis
- Reduced temperature
- Reduced 2,3-DPG
- Carbon monoxide
- Fetal Hb
71
List the causes of a right shift of the oxygen dissociation curve
- Acidosis
- Increased temperature
- Increased 2,3-DPG
- Carbon dioxide
- Altitude
72
Describe the Bohr effect
Right shift of the oxygen dissociation curve, the factors causing this are present in active tissues, it represents ma mechanism to increase oxygen extraction
73
Does anaemia affect the oxygen dissociation curve
No
74
Describe the structure of fetal Hb (differences from adult Hb)
Different globin chains = 2 alpha and 2 gamma
75
Purpose of fetal Hb
Has a greater affinity for O2 and allows the foetus to extract blood from the circulation
76
What is the function of myoglobin
Acts a storage molecule for oxygen - provides additional O2 in muscles during periods of anaerobic respiration
77
List the 3 methods of CO2 transport
1. Carbamino groups
2. Dissolved CO2 - 10%
3. HCO3 - 60-70%
78
Outline the process by which CO2 is transported as HCO3
1. CO2 diffuses into RBC
2. Reacts with water to form carbonic acid
3. Carbonic acid dissociates into H+ and HCO3-
4. H+ binds to Hb and the HCO3- diffuses out of the cell into plasma
5. To maintain balance CL- diffuses into the RBC (chloride shift)
79
Define the Haldane Effect
The amount of CO2 carried increases as the oxygen level falls
80
Where is the respiratory centre located
Medulla oblongata (contain inspiratory and expiratory nerurons)
81
What is the role of the Apneustic centre in the pons
Prolongs inspiration and results in short expiratory efforts
82
What is the role of the pneumotaxic centre in the pons
Inhibits inspiratory neurons and shortens inspiration
83
Where controls the ability to hold a breath
Cerebral cortex
84
Where are central chemoreceptors located
In the CNS, close to the respiratory centre of the medulla
85
How are central chemoreceptors stimulated
Sensitive to changes in arterial CO2:
1. CO2 reacts with water in the brain to produce H+
2. pH falls and directly stimulates the receptor
86
What is the most important stimulus to respiration
CO2
87
Where are the peripheral chemoreceptors located
1. Carotid body
| 2. Aortic bodies
88
What stimulates peripheral chemoreceptors
1. Hypoxia <8kPa
| 2. Changes in arterial pH
89
Describe the Hering-Breur reflex
Prevents lung overinflation - stretch receptors in the lung send inhibitory signals via the vagus
90
Define hypoxia
Deficiency of oxygen in the tissues
91
Define hypoxaemia
Reduction in the concentration of oxygen in the arterial blood
92
Define histotoxic hypoxia
Poisoning of the enzymes involved in cellular respiration. Oxygen is available but cannot be utilised. e.g. Cyanide poisoning
