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CR2 > 39 - High Altitude Physiology > Flashcards

39 - High Altitude Physiology Flashcards

1
Q

What is the effect on PaO2 at high altitudes?

A

Less paO2
Blood through lungs is less saturated
Pulmonary hypoxia and hypoxaemia

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2
Q

Where are hypoxia detectors

A

Carotid bodies

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3
Q

What causes decrease in ventilation at high altitudes

A

Excess blow of CO2
Causes alkalosis at central chemoreceptors
inhibits the increase in respiratory drive

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4
Q

When is the hypoxic drive from carotid bodies significant?

A

PO2 below 60mmHg

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5
Q

How is hypoxia worsened with rapid ascent to high altitude?

A

PaO2 in alveoli is low - pulmonary circulation VASOCONSTRICTS in hypoxia so worsens
= pulmonary artery hypertension

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6
Q

When is acclimatisation rapid and how long does it take?

A

to 2000m - usually within a day a or two

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7
Q

What happens up to 6000m

A

Fully acclimatised

well, reasonable appetite, normal sleep

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8
Q

What happens above 7000m

A

Hypoxia present
Tired
lethargy
Hard to walk

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9
Q

What happens above 7500m

A

Death Zone
Severe hypoxia
Physiological damage

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10
Q

What are the 3 mechanisms in acclimatisation

A

1 - metabolic acidosis
2 - Increase in erythrocyte number
3 - Reduced pulmonary vascular resistance

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11
Q

What causes the metabolic acidosis

A

Retention of acid

Increased excretion of bicarbonate in the kidney

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12
Q

What causes respiratory alkalosis at high altitude

A 
low PaO2
increased breathing rate
respiratory alkalosis
High pH
inhibits central chemoreceptors
Breathing decreases
Hypoxaemia
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13
Q

How does the body acclimatise to oppose the respiratory alkalosis

A

Kidneys decrease proton excreting ATP-ase in the kidney tubules so kidneys decrease renal excretion of acid and increase excretion of bicarbonate
- restores PH to normal

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14
Q

How is EPO production increased in acclimatisation? What is the result of this?

A

Hypoxaemia stimulates interstitial cells in the kidney
raise epo production
= increases the haematocrit
= increase the oxygen carrying capacity of the blood

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15
Q

Why is there a limit to maximum haematocrit?

A

Increase in haematocrit increases blood viscosity
Increases the pulmonary vascular resistance
can cause pulmonary arterial hypertension and RHF

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16
Q

Why does pulmonary vascular resistance fall?

A

Reduced hypoxic vasoconstriction

collateral circulations open up between pulmonary arteries and vens

17
Q

What mediates the decrease in hypoxic vasoconstriction?

A

Increased synthesis of nitric oxide in the pulmonary endothelium

18
Q

What is AMS

A

Acute Mountain Sickness

= The first sign that something is wrong

19
Q

HACE

A

High Altitude Cerebral Edema. Increased IC pressure. Can follow on from AMS if not treated. A serious neurological condition; fatal if not treated

20
Q

HAPE

A

High Altitude Pulmonary Edema. Equally serious pulmonary condition which can follow on from AMS.

21
Q

Signs and symptoms of AMS

A 
Headache
Poor Sleep
Tiredness
Loss of appetite, nausea, vomiting
Dizziness
22
Q

How do you diagnose AMS

A

The signs and symptoms are scored 0-3 and a score of more than 3 is needed for diagnosis

23
Q

Would you get AMS between 1500-2000m

A

Unlikely

may get mild illness

24
Q

Would you get AMS at 2500m

A

1 in 5 people have some symptoms if they ascend from sea level within a day - most will acclimatise in a day

25
Q

Would you get AMS at 5000m

A

Everyone will be temporary ill if they ascend within a few hours to 5000m
acclimatisation occurs but takes several days or more

26
Q

Treatment for AMS

A

IF mild then rest and no further ascent
IF severe then descent, oxygen, acetazolamide 250mg tds 3 times a day
Dexamethasone 4mg qds 4 times a day

27
Q

How do you prevent AMS

A 
Slow ascent (<300m per day over 3000m)
Avoid unnecessary exercise
Acetazolamide 250g
28
Q

What does acetazolamide do

A

Carbonic anhydrase inhibitor - increased bicarbonate excretion producing metabolic acidosis
compensates for the alkalosis caused by hyperventilation

29
Q

What is the effect of acetazolamide

A

less acid is secreted in the urine. The blood thus becomes acidified and respiration is stimulated.
= Speeds up acclimatization process
(read over the paragraph on this in notes, make sure u understand I cba to make qs about it)

30
Q

Why does High altitude cerebral oedema occur?

A

ATP decreases, Na pumps not working so Na leaks into nerve cells – pulls water = cell swelling

31
Q

Symptoms of brain swelling

A

Ataxia, nausea/hallucination, confusion, coma

32
Q

Treatment for HACE

A

Descend immediately, acetazolamide, oxygen, dexamethasone, hyperbaric chamber

33
Q

How does acetazolamide treat HACE

A

Reduces formation of CFS so reduces intracranial pressure

34
Q

How does high altitude pulmonary oedema occur

A

Pulmonary arterial hypertension - raised arterial and capillary pressure - fluid leaving blood and entering alveoli - worsens gas exchange

35
Q

Signs and symptoms of HAPO

A

Dysponea, reduced exercise tolerance, blood stained sputum, crackles on auscultation of chest

36
Q

Treatment of HAPO

A 
Descend immediately 
Sit patient upright
Oxygen
Nifedipine
Hyperbaric chamber
Viagra - sildenafil
37
Q

What is the action of nifedipine

A

Calcium channel blocker

Prevent the pulmonary arteries contracting

38
Q

What is the action of the hyperbaric chamber

A

increases the PaO2 of oxygen to improve oxygenation of blood - reduces hypoxic vasoconstriction

39
Q

What is the action of viagra - sildenafil

A

Pulmonary hypoxic vasoconstriction due to lack of NO - slows down the breakdown of cyclic GMP (vasodilator) - increases cyclin GMP levels
viagra relaxes pulmonary arteries and stops PAH and improves oxygenation of blood

CR2 (34 decks)

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