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Respiratory Physiology Flashcards

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1
Q

V

A

Volume of gas

L

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2
Q

V̇

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
Q

Ventilation at rest

A

0.5 L x 12 min = 6 L/min

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26
Q

Ventilation while exercising

A

3 L x 40 min = 120 L/min

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27
Q

Describe the equation V̇ ∝ (PB - PA)

A

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

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28
Q

Describe the equation V̇ = (PB - PA) / R

A

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

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29
Q

Sub-atmospheric pressure

A

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

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30
Q

Pip

A

Intrapleural pressure

Pressure within the pleural cavity, normally slightly less than barometric pressure and therefore considered negative

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31
Q

Describe the balance of forces during breathing

A

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

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32
Q

Where opposing forces are equal

A

At functional residual capacity

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33
Q

Describe why the intrapleural space is filled with fluid

A

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

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34
Q

Describe the equation Fcw = -FL

A

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

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35
Q

Pneumothorax

A

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

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36
Q

Describe how intrapleural pressure changes during a quiet breath

A

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
Q

Describe how alveolar pressure changes during a quiet breath

A

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
Q

Factors affecting air exchange

A 
Muscular effort
Compliance
Resistance
Dead space
Diffusion
39
Q

Pulmonary compliance

A

A measure of the distensibility of the lungs and chest wall

The change in volume that accompanies a small change in pressure

40
Q

Describe the equation Compliance = ΔV / ΔP

A

Compliance = change in volume divided by change in pressure

A small change in pressure + large volume change = high compliance

41
Q

Describe how compliance is affected in emphysema

A

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
Q

Elastance

A

Describes the stiffness of the lung tissue

43
Q

Resistance

A

ΔP / ΔFlow

44
Q

Describe why air filled lungs are less compliant than saline filled lungs

A

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
Q

Describe resistance at different stages of the airways

A

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
Q

Anatomic dead space

A

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
Q

Describe where oxygen and carbon dioxide move between

A

Between alveoli and pulmonary capillary blood

Between systemic capillary blood to cells

48
Q

Ficks Law

A

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
Q

Respiratory Distress Syndrome

A

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
Q

Emphysema

A

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
Q

Asthma

A

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
Q

Pulmonary edema

A

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
Q

The universal gas law

A

P = nRT / V

The pressure of a gas is inversely related to its volume

54
Q

Daltons law

A

P(total) = ΣP

Total pressure of gas is equal to the sum of pressures of each of its parts

55
Q

Henrys law

A

C = σP
Concentration of a dissolved gas varies directly with its partial pressure
σ is a solubility constant depending on the gas

56
Q

Oxygen content of blood

A

Total amount of oxygen carried in whole blood

Sum of oxygen combined with haemoglobin inside erythrocytes and oxygen dissolved in plasma

57
Q

Amount of oxygen that can be bound to haemoglobin per litre of blood

A

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
Q

Saturation of haemoglobin

A

Amount of oxygen actually bound to haemoglobin relative to the maximum amount that could be bound (normally 200 mL per L of blood)

59
Q

Normal saturation level of haemoglobin

A

98% (arterial blood)
197 mL oxygen per litre of blood bound to haemoglobin
Other 3 mL dissolved in plasma

60
Q

Cooperative binding

A

The first oxygen molecule is difficult to bind haemoglobin but binding becomes progressively easier as more oxygen binds haemoglobin

61
Q

Effect of pH on affinity of haemoglobin for oxygen

A

High blood pH (7.6) increases haemoglobin saturation

Low blood pH (7.2) decreases haemoglobin saturation

62
Q

Effect of carbon dioxide partial pressure on affinity of haemoglobin for oxygen

A

Low blood CO2 increases haemoglobin saturation

High blood CO2 decreases haemoglobin saturation

63
Q

Factors affecting the haemoglobin-oxygen equilibrium

A

pH decrease
CO2 partial pressure increase
temperature increase
All 3 of these occur during exercise in order to offload oxygen into tissues faster

64
Q

Effect of anaemia on oxygen transport

A

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
Q

Effect of carbon monoxide of oxygen transport

A

Carbon monoxide has a much higher affinity for haemoglobin than oxygen so oxygen binding in blocked
Less oxyhaemoglobin saturation causing no sigmoidal relationship

66
Q

Describe why a sigmoidal curve is desirable for haemoglobin saturation

A

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
Q

Summarise gas exchange and transport in lungs and tissues using haemoglobin onload and offload

A

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
Q

Describe the equation V̇A = fR x (VT - VD)

A

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
Q

Hyperventilation

A

Rapid breathing
Eliminating CO2 at a faster rate than metabolism can produce it
Raises alveolar O2 partial pressure towards inspiration rate

70
Q

Consequences of hyperventilation

A

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
Q

Hypoventilation

A

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
Q

Consequences of hypoventilation

A

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
Q

Describe the response to altered inspiratory partial pressures of oxygen and carbon dioxide

A

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
Q

Respiratory centres in the CNS

A

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
Q

DRG

A

Dorsal Respiratory Group

Medullary centre containing neurons primarily active during inspiration

76
Q

VRG

A

Ventral Respiratory Group
Medullary centre containing neurons with activity split between inspiration, expiration and the transition between the two

77
Q

Airway feedback

A

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
Q

Chemoreceptor feedback

A

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
Q

Carotid bodies

A

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
Q

Aortic bodies

A

Found in the aortic arch and subclavian arteries

Afferents travel in the vagus nerve

81
Q

Intrinsic sensitivity to oxygen and carbon dioxide arterial partial pressures

A

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
Q

Residual volume calculation

A

FRC - ERV

1200 mL

83
Q

Tidal volume calculation

A

Inspiratory capacity - IRV

500 mL

84
Q

Functional residual capacity calculation

A

ERV + residual volume

2400 mL

85
Q

Total lung capacity calculation

A

Vital capacity + residual volume

6000 mL

86
Q

Vital capacity calculation

A

IRV + ERV + tidal volume

4800 mL

87
Q

Expiratory reserve volume

A

1200 mL

Amount that can be actively expired past normal tidal breathing, not including residual volume

88
Q

Inspiratory reserve volume

A

3100 mL

Amount that can be actively inspired past normal tidal breathing

Medical Science (11 decks)

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