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HUMB3001 > W3 - Diving Physiology > Flashcards

W3 - Diving Physiology Flashcards

1
Q

What law do gases follow?

A

Boyle’s Law

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2
Q

What is Boyle’s Law?

A

Pressure (p) of a given quantity of gas (n) varies inversely with its volume (v) at constant temperature (T)

P1 V1 = P2 V2

At 40 m below sea level (5 atmospheres) the volume is 1/5 of what it is at sea level

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3
Q

What happens during breath hold dive?

A

Volume of air in lungs gradually decreases with increasing depth

As pressure of gas increases, density increases

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4
Q

What is Dalton’s Law?

A

In gas mixture, an increase in total gas pressure is associated with an increase in partial pressures of gases by same proportion

P total = P 1 + P2

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5
Q

What is Henry’s Law?

A

As partial pressure of gas is increased so the amounts of gas dissolved in body’s liquids increase

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6
Q

What are the direct effects of increase pressure?

A

Cardiovascular changes (diving response)
Barotrauma
High pressure neurological syndrome (HPNS)

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7
Q

Describe hydrostatic pressure.

A

pressure of the blood against the wall due to gravity

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8
Q

Describe blood pressure in body when on land in upright position

A

Gravity acting through longitudinal axis
Hydrostatic pressure gradient down body
BP in lower half of body increases
Result = pooling of blood in lower half

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9
Q

Describe pressure gradients in body when surrounded by water

A

Equal external hydrostatic pressure gradient down body which opposes internal hydrostatic pressure gradient

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10
Q

What is impact to blood when person is immersed in water?

A

500mL of blood moves from lower half of body to thoracic regions

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11
Q

What is impact to CVS when person is immersed in water?

A

Incr in central blood volume = incr right atrial pressure = incr stroke volume = incr cardiac output = incr pulmonary blood flow = incr blood volume = incr pulmonary diffusing capacty

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12
Q

What is effect of increased central blood volume?

A

Decrease in release of vasopressin (ADH) (water absorption)

Increased secretion of atrial natriutic hormone (water secretion)

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13
Q

What happens on first immersion of body in water when colder than 15 deg C?

A

Heart rate falls
Breathing ceases
Selective vasoconstriction occurs

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14
Q

What is effect of the diving response?

A

Heart rate falls
Breathing ceases
Selective vasoconstriction occurs

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15
Q

What causes diving response?

A

Stimulation of cutaneous receptors on face by cold water

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16
Q

What is role of diving response?

A

Conserve oxygen in diving mammals
Decreasing workload of heart
Decreasing blood flow to most of systemic circulation except for brain/heart

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17
Q

What happens to air in lungs during breath hold dive?

A

As person goes deeper

Volume of air in lungs decreases

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18
Q

When is breath hold dive a problem?

A

When volume of lung gases are compressed beyond residual volume

Causes negative intra-alveolar pressure = lung squeeze, pulmonary congestion, oedema, haemorrhage

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19
Q

What happens when diver with compressed air ascends?

A

Pulmonary barotrauma can occur

If driver fails to exhale during ascent or gas is trapped in area of lung = alveolar rupture

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20
Q

What happens during ascent of breath hold dive?

A

Gases in lung re-expand to original volume

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21
Q

What must be given to divers when going deeper than 0.5 m?

A

Supplied with breathing mixture at a pressure equal to ambient pressure

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22
Q

What is given to SCUBA divers?

A

Cylinder of compressed air (21% O2, 78% N2)

Demand valve ensures air is provided at pressure to match ambient pressure

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23
Q

What changes occur to gases under pressure?

A

Density of gases increases

Partial pressure of gases increases

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24
Q

What is effect of increased air density?

A

Increases inspiratory effort = work of breathing
Slow intra-alveolar diffusion of gases
Reduced maximum aerobic capacity (VO2 max)

Reduce by replacing N2 with helium

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25
Q

When does nitrogen narcosis occur?

A

When compressed air is used during diving, partial pressure of nitrogen increases and symptoms develop at 30 m below sea (4 atm)

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26
Q

What are raptures of the deep?

A

Symptoms of nitrogen narcosis

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27
Q

What are symtpoms of nitrogen narcosis?

A 
Resemble alcohol intoxication
Euphoria
Irrational
Reduced dexterity
Reduced mental agility
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28
Q

What depths does nitrogen narcosis cause unconsiousness?

A

Beyond 90 msw (10 atm)

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29
Q

How does nitrogen produce narcosis?

A

Nitrogen causes small change in membrane volume
Leads to modulation of ion channels
Disruption of excitability of axons
Impairment of synaptic transmission

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30
Q

What is HPNS?

A

High pressure neurological syndrome

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31
Q

What parts of body compress at higher pressures?

A

Lipids more compressible than water

Gases

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32
Q

What causes HPNS?

A

Compression of lipids in cell membranes of neurons

Changes permeability and transport properties

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33
Q

What are symptoms of HPNS?

A

Tremor
Decr manual dexterity
Dizziness
Nausea

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34
Q

What depths (atmospheres) is HPNS seen?

A

Below 200 msw or over 21 atm

Severe when rate of descent is rapid

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35
Q

What happens when PO2 rises above 1350mmHg?

A

Oxygen is toxic to nervous system
Can cause epileptic type convulsions

Preceded by vertigo, nausea, paraesthesia of arms/legs, twitching muscles around eye/mouth

36
Q

What depth do you reach toxic PO2 when breathing pure oxygen?

A

8 msw (when PO2 is 1.8 atm = 1350 mmHg)

37
Q

Why is oxygen toxic to CNS?

A

Possibly due to oxidation of sulphydryl groups found in some enzymes and membrane protiens

Disrupt function and hyperexcitability of neurons

38
Q

What are initial symptoms of pulmonary oxygen toxicity?

A

Coughing -> dyspnoea (difficult breathing) -> pulmonary oedema -> intra-alveolar haemorrhage

39
Q

What causes symptoms of pulmonary oxygen toxicity?

A

Progressive destruction of alveolar endothelial and epithelial cells

40
Q

What PO2 can pulmonary toxicity develop in?

A

As little as 375mmHg (0.5 atm) so when 16 msw (compressed air)

Symptoms appear after > 30h

41
Q

What gas mixture do divers use for below 50 msw?

A

Helium oxygen mixture

42
Q

Why is helium used in mixtures?

A

1/8 th narcotic effects of nitrogen so higher PP can be withstood

1/7th density of nitrogen so work of breathing is reduced

Solubility is 40% of nitrogen

Reduces likelihood of decompression sickness

43
Q

Describe important of heliox mixture.

A

Ratio of helium - oxygen is adjusted so PO2 does not exceed 300 mmHg

At 100msw, % O2 used is 4.4%
At 300msw, % O2 used is 1.26%

44
Q

What are other effects of helium?

A

High thermal conductivity = increased resp heat losses

Helium elevates pitch of voice (low density)

45
Q

What is trimix and what depths used for?

A

Mixture of O2, N2, Helium

Deeper than 50m (non-recreational)

46
Q

Why was trimix developed?

A

Exploit the known depressant effect of nitrogen on NS to offset excitatory effects of high pressure

47
Q

What depths can be achieved with trimix?

A

> 650m

48
Q

Describe dissolution of N2 in body solution in diving descent.

A

At sea level: 1L of N2 in solution
Every 10m: Another 1L of N2 more

New equilibrium is not attained immediately

49
Q

Describe equilibrium process of N2 in body

A

Blood volume is 8% of body volume so takes time for nitrogen to be transported to tissues and reach equilibrium

Well perfused tissues (brain) take up N2 and reach equilibrium quickly
Adipose tissue (slower perfusion) reaches equilibrium slower

Usually takes 6-8h for all tissues to reach equilibrium

50
Q

Define saturation diving.

A

When tissues reach equilibrium of the inhaled gases

51
Q

What is the problem with gas mixtures when diving?

A

Not with uptake but problems to eliminate them when decompression takes place on ascent

52
Q

What happens to gases when divers ascend?

A

Inspired gas pressures fall
Partial pressure gradient for gases develops between tissues and alveoli
Extra gases diffuse from tissues into blood to be eliminated in lungs

53
Q

Describe effect when rate of ascent is rapid.

A

There is maximal rate at which gases can be eliminated
If quantity of gases dissolved in tissues is large, tissues become supersaturated causing them to come out of solution and form bubbles

Decompression sickness = bends

54
Q

Which type of gases are important in decompression sickness?

A

Inert gas bubbles that cannot be utilised by tissues

55
Q

What can O2 bubbles be used for?

A

Locally in tissue metabolism

56
Q

What is impect of body fat % on decompression?

A

Higher body fat means more nitrogen stored which needs to be eliminated

57
Q

What is example of barotrauma?

A

Alveoli ruptured and gas escapes into pleural cavity causing pneumothroax

58
Q

Describe cause of cerebral arterial gas embolism

A

Aveoli ruptured, gas escape into pulmonary circulation where reaches systemic circulation

Pass upwards via carotid arteries to cerebral circulation

59
Q

What are symptoms and treatment of cerebral arterial gas embolism?

A

Stroke like symptoms, lose consciousness

Treated by recompression to 6 atm

60
Q

What is effect of high pressure on rigid body cavities e.g. paranasal sinus/middle ear?

A

Not free to undergo change in volume
Bound by rigid structures
If pressure of gas cannot equilibrate with ambient pressure
Risk of damage to structures

61
Q

What is effect of high pressures on mucosal linings of cavities?

A

Large transmural (across entire BV) pressure across vasculature will lead to exudation of fluid

Can lead to rupture of capillaries

62
Q

How is barotrauma to middle ear prevented?

A

By equilibrating pressure in middle ear with ambient pressure

63
Q

What happens if Eustachian tube entrance is blocked/inflamed during high pressure?

A

Equilibration may become impossible

Descent causes significant pressure gradient to develop across tympanic membrane = bulge inwards = pain

64
Q

What happens if channels between paranasal sinus to nasopharynx are blocked (sinusitis) during descent?

A

Equalisation cannot occur

Haemorrhage of lining of sinuses and intense pain

65
Q

List some scuba diving hazards resulting from inability to equalise pressure.

A 
Air embolism in brain
Face mask squeeze = rupture BV in eyes, suck eyes from sockets
Mediastinal and subcutaneous emphysema
Pneumothorax
Alveoli ruptured
66
Q

What is underlying cause of decompression sickness?

A

Formation of inert gas bubbles

67
Q

When does decompression sickness cause overt symptoms?

A

When bubbles reach some critical size

68
Q

What factors predispose people to decompression sickness?

A

Obesity
Poor physical condition
Age
Exertion

69
Q

What are the 3 theories of why bubbles cause decompression sickness?

A

Direct mechanical effects of EC bubbles, distorting tissues, blocking capillaries

Cellular damage due to intracellular gases

Changes in vascular endothelium, aggregation of intravascular fat, imposed by intravascular bubbles

70
Q

When do signs and symptoms of decompression sickness occur?

A

90% appear within 6h

May not occur until 36h after

71
Q

What is most common symptom of decompression sickness?

A

Pain in joints of extremities (shoulder, elbow, knee) = formation of bubbles in ligaments, tendons

72
Q

Where do larger intravascular bubbles usually get trapped?

A

Pulmonary vascular bed

73
Q

What happens to bubbles in pulmonary vascular bed?

A

Block pulmonary capillaries

Causes severe dyspnoea and cough

74
Q

What is chokes?

A

Severe dyspnoea and cough from bubbles trapped in pulmonary vascular bed

75
Q

What causes serious form of decompression sickness?

A

When bubbles form in spinal cord or when intravascular bubbles block circulation to cord

Degenerates nerve fibers causing motor/sensory deficits = permanent paralysis

76
Q

What is staggers?

A

Bubble formation in vestibular apparatus

77
Q

What is bone avascular necrosis?

A

Bubbles blocking end artiers of bone causing bone to die

Head/neck/shaft of long bones (upper humerus, upper/lower femur, upper tibia)

78
Q

How is decompression sickness avoided?

A

Select rate of ascent that precludes significant bubble formation

Use decompression table

79
Q

What did Haldane suggest about bubble formation?

A

Significant bubble formation would not occur if total tissue gas pressure did not exceed 2x ambient pressure

80
Q

What are decompression tables?

A

Shows divers how to ascend
Where to stop (depths)
Where ambient pressure is half of that at the depth of previous stop
How long to stop to allow inert gas to be eliminated (equilibrium attained)

81
Q

What ascent is recommended after diving to 20 msw for 2h?

A

2 stops taking 50 min in total

82
Q

What ascent is recommended after diving to 50 msw for 45min?

A

5 stops, total 85 min

83
Q

What is decompression time for diving at 100 msw?

A

4 days

84
Q

What is decompression time for diving at 300 msw?

A

10 days

85
Q

What actions must divers avoid after diving?

A

Avoid flying in aircraft

Ambient pressure in aircraft is less than normal pressure so further decrease in pressure can cause bubble formation

86
Q

What are some other problems associated with diving?

A

Density of water increases effort to move
Difficult to use tools with torque due to buoyancy
Visibility is impaired
Hearing is impaired
Cold (water conducts heat away)

87
Q

Describe impact of cold water in diving.

A

Water surrounding diver conducts heat away from body surface

Wet suit can be used but thermal insulation decreases with increasing depth due to compression of suit

Heliox exaggerates heat loss (incr respiratory heat loss)

Need own central heating system = electrically heated suit/hot water piped in suit

HUMB3001 (8 decks)

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