Respiratory Physiology Flashcards

(88 cards)

1
Q

V

A

Volume of gas

L

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2
Q

A

Rate of change of volume of a gas

L/min

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3
Q

P

A

Pressure

mmHg

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4
Q

F

A

Fractional concentration of a gas

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5
Q

C

A

Content of a gas in blood

mL/L

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6
Q

f

A

Frequency of respiration

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7
Q

I

A

Inspired gas

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8
Q

E

A

Expired gas

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9
Q

A

A

Alveolar

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10
Q

T

A

Tidal

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11
Q

D

A

Dead space

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12
Q

B

A

Barometric

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13
Q

a

A

Arterial

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14
Q

v

A

Venous

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15
Q

c

A

Capillary

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16
Q

FAO2

A

Fraction of O2 in alveolar air

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17
Q

V̇O2

A

Volume of O2 consumed per minute

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18
Q

PcO2

A

Partial pressure of O2 in capillary blood

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19
Q

Total lung capacity

A

Achieved by maximal inspiration

The largest amount of air that can possibly be held in the lungs

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20
Q

Maximal inspiration

A

The maximum amount of air you can inhale

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21
Q

Maximal expiration

A

Maximum amount of air you can exhale - not all air can be expelled from the lungs

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22
Q

Tidal volume

A

VT

The volume of a single breath

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23
Q

Functional residual capacity

A

Amount of air in the lungs at the end of a normal relaxed expiration

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24
Q

Residual volume

A

VR

Minimal volume of air that can be left in the lung

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25
Ventilation at rest
0.5 L x 12 min = 6 L/min
26
Ventilation while exercising
3 L x 40 min = 120 L/min
27
Describe the equation V̇ ∝ (PB - PA)
Rate of flow is directly proportional to the barometric/alveolar pressure gradient In order for air to move a pressure gradient must exist so air can only enter the lungs if alveolar pressure is less than barometric pressure. The wider the difference the faster air can flow The pressure gradient is caused when the ribcage expands, increasing thoracic volume and decreasing alveolar pressure Alveolar pressure increases with the inhalation of air into the lungs. When the alveolar pressure excess the barometric pressure exhalation occurs
28
Describe the equation V̇ = (PB - PA) / R
Rate of flow equal to the barometric/alveolar pressure gradient divided by the resistance to air flow The rate at which the lungs expand or deflate is reduced by any factor that increases resistance to air flow allowing the direct proportionality to be converted into a calculable equation
29
Sub-atmospheric pressure
When alveolar pressure is less than barometric pressure it is considered sub-atmospheric Occurs whens thoracic volume increases by descent of diaphragm and rib cage elevation
30
Pip
Intrapleural pressure | Pressure within the pleural cavity, normally slightly less than barometric pressure and therefore considered negative
31
Describe the balance of forces during breathing
The lungs experience a force that causes a tendency for them to collapse because of elastic recoil from stretched elastic fibres and surface tension from surfactant The chest wall experiences a force that causes a tendency for it to spring outward because of stretched tissues in the sterno-costal and costo-vertebral joints The collapsing tendency exactly counteracts the expanding tendency causing equilibrium at functional residual capacity
32
Where opposing forces are equal
At functional residual capacity
33
Describe why the intrapleural space is filled with fluid
Serous fluid in the IP space connects the lungs and the ribcage via the parietal and visceral pleura. The moist membranes are impossible to pull apart and so move together to achieve equilibrium of the opposing forces
34
Describe the equation Fcw = -FL
The force of the chest wall is equal to the opposite force of the lung Occurs when the lung relaxes and brings the chest wall with it and vice versa
35
Pneumothorax
A penetrating injury of the chest wall resulting in a connection between the external environment and the intrapleural space Pressure gradients between the intrapleural space and lung can't be set up because the intrapleural pressure is equal to the barometric pressure - 0 The intrapleural space can't increase the volume and decrease the pressure meaning the lungs can't move with it and expand when the diaphragm and external intercostal muscles contract Introduction of air into the intrapleural space disrupts the adhesive forces set up by the serous fluid, allowing the visceral and parietal pleura to move apart and resulting in a collapsed lung
36
Describe how intrapleural pressure changes during a quiet breath
In a human lung the intrapleural pressure is always slightly subatmospheric so at rest the pressure is around -3 mmHg Diaphragm and external intercostal muscles contract causing active inspiration as the intrapleural pressure decreases to about -5 mmHg Passive expiration occurs by relaxation of the diaphragm and external intercostal muscles, decreasing the volume of the intrapleural space and thus increasing the intrapleural pressure back to -3 mmHg
37
Describe how alveolar pressure changes during a quiet breath
Immediately before inspiration alveolar pressure is equal to barometric pressure, therefore 0 mmHg Contraction of the diaphragm and external intercostal muscles enlarges the thoracic cavity, increasing the volume and decreasing the alveolar pressure to subatmospheric levels around -1 mmHg The area of the curve during active inspiration is equal to the peak of tidal volume Alveolar pressure returns to barometric pressure causing the diaphragm and external intercostal muscles to relax Intrapleural pressure rises and the lungs recoil causing the gases still in the alveoli to become compressed and increasing the alveolar pressure causing a pressure gradient pushing the air back from the lungs to the atmosphere
38
Factors affecting air exchange
``` Muscular effort Compliance Resistance Dead space Diffusion ```
39
Pulmonary compliance
A measure of the distensibility of the lungs and chest wall | The change in volume that accompanies a small change in pressure
40
Describe the equation Compliance = ΔV / ΔP
Compliance = change in volume divided by change in pressure | A small change in pressure + large volume change = high compliance
41
Describe how compliance is affected in emphysema
Destruction of elastic fibres in the alveolar walls causes inability to recoil, therefore increased compliance Little pressure required to fill lungs during inspiration but because lungs are limp and soft without elastic fibres expiration is much more difficult resulting in shortness of breath
42
Elastance
Describes the stiffness of the lung tissue
43
Resistance
ΔP / ΔFlow
44
Describe why air filled lungs are less compliant than saline filled lungs
Alveoli has moist surface meaning under normal circumstance an air-water surface tension exists that must be overcome during inspiration When filling a lung with saline no air-water interface exists meaning less pressure needs to be overcome and disrupting the compliance = ΔV / ΔP equation to the point where compliance is massively increased in a saline filled lung
45
Describe resistance at different stages of the airways
Resistance starts high in the trachea and increases through the bronchi . It is highest at the level of the tertiary bronchi and decreases rapidly as total cross sectional area increases in the smaller respiratory airways Resistance is highest in the smallest airways when looking at them individually because it varies inversely with airway radius, however the small airways tend to be arranged in parallel meaning the TOTAL resistance is lowest in the smallest airways
46
Anatomic dead space
The volume of the conducting airways About 3% of total lung capacity Air that consists of no oxygen that you can never get rid of - always the first to enter the lung and the last to leave but owing to the fact you can only inhale and exhale so much, this dead air takes up valuable space in the lung and is consistently taken in and out with every breath Dilution of tidal inspiration with alveolar air remaining from previous expiration
47
Describe where oxygen and carbon dioxide move between
Between alveoli and pulmonary capillary blood | Between systemic capillary blood to cells
48
Ficks Law
Volume of gas transported across a membrane per unit of time is directly related to the difference in partial pressure of the gas across the membrane and the area of the membrane Volume of gas transported across a membrane per unit of time is inversely related to the length of the diffusion pathway and the square root of the molecular weight of the gas
49
Respiratory Distress Syndrome
Common in premature babies because of underdeveloped surfactant Air-water interface in the alveoli causes surface tension. Sufficient pressure is needed to overcome both the elastic recoil of the lung tissue and the air-water surface tension Decreased surfactant means higher intrapleural pressure is required to separate the pleura and inflate the lungs - more muscular effort needed causing fatigue
50
Emphysema
Characterised by destruction of alveolar and peribronchial tissue which normally holds the smallest bronchioles open during expiration Destruction causes bronchiole collapse upon expiration causing trapped air in the donwstream alveoli and a condition called barrel chest - you can get air in but not out, impairing passive deflation Functional Residual Capacity is increased and disadvantages inspiratory muscles
51
Asthma
Characterised by bronchiolar restriction by smaller radius Increased resistance in the bronchioles which increases the pressure required to achieve tidal volume and therefore increased muscular effort
52
Pulmonary edema
Characterised by increased diffusion distance by fluid build up in the tissues and the lungs Decreased gas exchange causing shortness of breath Can be treated somewhat by increasing partial pressure of oxygen
53
The universal gas law
P = nRT / V | The pressure of a gas is inversely related to its volume
54
Daltons law
P(total) = ΣP | Total pressure of gas is equal to the sum of pressures of each of its parts
55
Henrys law
C = σP Concentration of a dissolved gas varies directly with its partial pressure σ is a solubility constant depending on the gas
56
Oxygen content of blood
Total amount of oxygen carried in whole blood | Sum of oxygen combined with haemoglobin inside erythrocytes and oxygen dissolved in plasma
57
Amount of oxygen that can be bound to haemoglobin per litre of blood
200 mL per L of blood | Whole blood of healthy adults contains about 150g of haemoglobin per litre of blood, each gram binding 1.34 mL oxygen
58
Saturation of haemoglobin
Amount of oxygen actually bound to haemoglobin relative to the maximum amount that could be bound (normally 200 mL per L of blood)
59
Normal saturation level of haemoglobin
98% (arterial blood) 197 mL oxygen per litre of blood bound to haemoglobin Other 3 mL dissolved in plasma
60
Cooperative binding
The first oxygen molecule is difficult to bind haemoglobin but binding becomes progressively easier as more oxygen binds haemoglobin
61
Effect of pH on affinity of haemoglobin for oxygen
High blood pH (7.6) increases haemoglobin saturation | Low blood pH (7.2) decreases haemoglobin saturation
62
Effect of carbon dioxide partial pressure on affinity of haemoglobin for oxygen
Low blood CO2 increases haemoglobin saturation | High blood CO2 decreases haemoglobin saturation
63
Factors affecting the haemoglobin-oxygen equilibrium
pH decrease CO2 partial pressure increase temperature increase All 3 of these occur during exercise in order to offload oxygen into tissues faster
64
Effect of anaemia on oxygen transport
Haemoglobin is reduced which in turn substantially reduces the total oxygen bound even though haemoglobin saturation level is still 98% Fall in oxygen levels causes no shift but the sigmoidal curve becomes depressed
65
Effect of carbon monoxide of oxygen transport
Carbon monoxide has a much higher affinity for haemoglobin than oxygen so oxygen binding in blocked Less oxyhaemoglobin saturation causing no sigmoidal relationship
66
Describe why a sigmoidal curve is desirable for haemoglobin saturation
Partial pressure drives diffusion so it is ideal to keep this value relatively stable A sigmoidal curve allows a large drop in haemoglobin saturation with only a small drop in partial pressure
67
Summarise gas exchange and transport in lungs and tissues using haemoglobin onload and offload
Haemoglobin binds oxygen in the lungs Oxyhaemoglobin moves to tissues where oxygen is offloaded Oxygen is converted into carbon dioxide and water All oxygen is used up in the tissues. Haemoglobin is forced to pick up carbon dioxide because of lack of oxygen Carboxyhaemoglobin moves back to the lungs where carbon dioxide is offloaded Haemoglobin is now free to pick up oxygen again
68
Describe the equation V̇A = fR x (VT - VD)
The alveolar volume is the difference between the tidal volume and the dead space volume The rate at which the alveolar volume is ventilated is proportional to the alveolar volume and the frequency of breathing
69
Hyperventilation
Rapid breathing Eliminating CO2 at a faster rate than metabolism can produce it Raises alveolar O2 partial pressure towards inspiration rate
70
Consequences of hyperventilation
Accumulation of oxygen in alveoli leads to increased alveolar and arterial oxygen partial pressures Decrease of carbon dioxide in the alveoli leads to decreased alveolar and arterial carbon dioxide partial pressures, increase of arterial pH and respiratory alkalosis Eventually alkalotic coma
71
Hypoventilation
Slow or absent breathing Carbon dioxide builds up by metabolism in the body but is not expired quickly enough Decreases alveolar oxygen partial pressure
72
Consequences of hypoventilation
Decreases oxygen in the alveoli leads to decrease oxygen alveolar and arterial partial pressures Accumulation of carbon dioxide in the alveoli increases alveolar and arterial carbon dioxide partial pressure, decreases pH and causes respiratory acidosis Eventually acidotic coma
73
Describe the response to altered inspiratory partial pressures of oxygen and carbon dioxide
Respiratory system is unaware of oxygen content of any tissue and is unaware of venous oxygen partial pressure Not very responsive to arterial oxygen partial pressures Appears to be more sensitive to carbon dioxide partial pressures - sensed centrally and peripherally by chemoreceptors
74
Respiratory centres in the CNS
Breathing relies on neural input to ventilation muscles from the medulla oblongata Basic rhythm determined by two groups of neurons in medulla called DRG and VRG The brainstem communicates with cranial motor neurons and spinal cord which cause contraction of ventilation muscles
75
DRG
Dorsal Respiratory Group | Medullary centre containing neurons primarily active during inspiration
76
VRG
Ventral Respiratory Group Medullary centre containing neurons with activity split between inspiration, expiration and the transition between the two
77
Airway feedback
Slowly adapting stretch receptors in the bronchi and bronchiole walls send signals via the vagus nerve to respiratory centres Irritant sensors in airways respond to noxious mechanical and chemical stimuli, histamine and prostaglandins, lung hyperinflation
78
Chemoreceptor feedback
Peripheral sensors in the carotid bodies and aortic bodies detect arterial oxygen and carbon dioxide partial pressures, informing the central respiratory control centre if more ventilation is required to maintain appropriate gas levels Central sensors on the ventral surface of the medulla are sensitive to cerebrospinal fluid pH
79
Carotid bodies
Located at the bifurcation of the common carotid arteries Highly vascularised Well suited to sense oxygen and carbon dioxide levels in the blood Respond to decrease of oxygen arterial partial pressure or increase of carbon dioxide arterial partial pressure Afferents from carotid bodies travel along carotid sinus nerve which joins the IXth cranial glossopharyngeal nerve as it enters the medulla
80
Aortic bodies
Found in the aortic arch and subclavian arteries | Afferents travel in the vagus nerve
81
Intrinsic sensitivity to oxygen and carbon dioxide arterial partial pressures
Ventilation is most sensitive to peripheral arterial carbon dioxide partial pressure and central medullary pH The body is very sensitive to both carbon dioxide and oxygen but oxygen sensitivity is masked to keep carbon dioxide to a non-poisonous level
82
Residual volume calculation
FRC - ERV | 1200 mL
83
Tidal volume calculation
Inspiratory capacity - IRV | 500 mL
84
Functional residual capacity calculation
ERV + residual volume | 2400 mL
85
Total lung capacity calculation
Vital capacity + residual volume | 6000 mL
86
Vital capacity calculation
IRV + ERV + tidal volume | 4800 mL
87
Expiratory reserve volume
1200 mL | Amount that can be actively expired past normal tidal breathing, not including residual volume
88
Inspiratory reserve volume
3100 mL | Amount that can be actively inspired past normal tidal breathing