gas transport

Question 1

define hypoxia

Answer 1

specific environment with low PO2 (conditions)

Question 2

define hypoxaemia

Answer 2

low PaO2 in blood

Question 3

define ischaemia

Answer 3

tissues receiving inadequate oxygen

Question 4

what can bring on hypoxic stress

Answer 4

altitude, exercise, disease (e.g. COPD)

Question 5

what changes when low PO2 (still 21%) at high altitude and what detects this change

Answer 5

low PAO2 (alveolar) and low PaO2 (arterial), activating peripheral chemoreceptors (as opposed to central control using PCO2)

Question 6

what outflow increased after low PaO2 detected

Answer 6

sympathetic nervous system

Question 7

what 2 responses occur after increased sympathetic nervous system outflow

Answer 7

increased ventilation to increase alveolar oxygen and oxygen loading; increase cardiac output and heart rate to increase oxygen loading and tissue delivery

Question 8

however what does hyperventilation lead to and what is the effect

Answer 8

hypocapnia, reducing central drive to breathe, reducing ventilation and hence oxygen loading

Question 9

what does the CO2 loss cause

Answer 9

increased pH (alkalosis), shifting oxygen-dissociation curve left, increasing Hb affinity for O2 and causing decreased O2 unloading

Question 10

what detects high pH

Answer 10

carotid bodies

Question 11

what is the response to high pH

Answer 11

increased HCO3- secretion and causing kidneys to recover and manufacture more H+, normalising oxygen-dissociation curve to increase oxygen unloading

Question 12

what does low PaO2 also increase

Answer 12

erythropoietin production, increasing erythrocyte production and oxygen unloading

Question 13

why do oxidative enzyme/mitochondrial numbers increase

Answer 13

to allow for greater oxygen utilisation to provde energy

Question 14

why is there a small 2,3-DPG increase

Answer 14

shift of oxygen-dissociation curve to right, increasing oxygen unloading

Question 15

diagram of response to altitude

Answer 15

benjis

Question 16

2 prophylaxis to high altitude

Answer 16

acclimation (stimulated by artificial environments e.g. hyperbaric chamber), acetazolamide (carbonic anhydrase inhibitor to accelerate slow renal compensation to hypoxia induced hyperventilation)

Question 17

cause of acute mountain sickness

Answer 17

maladaptation to high altitude, with onset within 24 hours of ascent

Question 18

pathophysiology of acute mountain sickness

Answer 18

mild cerebral oedema

Question 19

symptoms of acute mountain sickness

Answer 19

nausea and vomiting, irritability, dizziness, insomnia, fatigue, dyspnoea

Question 20

consequences of acute mountain sickness

Answer 20

HAPE/HACE progression (high altitude pulmonary and cerebral oedemas)

Question 21

treatments of acute mountain sickness

Answer 21

stop ascent, analgesia, fluids, hyperbaric O2 therapy

Question 22

cause of chronic mountain sickness

Answer 22

idiopathic

Question 23

pathophysiology of chronic mountain sickness

Answer 23

secondary polycythaemia increases blood viscosity (higher Hct), so blood sludges through systemic capillaries, impeding O2 delivery

Question 24

symptoms of chronic mountain sickness

Answer 24

cyanosis (bluish discolouration), fatigue

Question 25

treatment of chronic mountain sickness

Answer 25

remain at low altitude

Question 26

causes of high altitude pulmonary oedema

Answer 26

rapid ascent and inability to acclimatise

Question 27

pathophysiology of high altitude pulmonary oedema

Answer 27

pulmonary vessel vasoconstriction in response to hypoxia, causing increased pulmonary pressure and permeability which exceeds lymphatic drainage

Question 28

symptoms of high altitude pulmonary oedema

Answer 28

dyspnoea, dry cough, bloody sputum, crackling chest sounds

Question 29

consequences of high altitude pulmonary oedema

Answer 29

impaired gas exchange

Question 30

treatments for high altitude pulmonary oedema

Answer 30

descend, hyperbaric O2 therapy, nifedipine, sildenafil

Question 31

causes of high altitude cerebral oedema

Answer 31

rapid ascent and inability to acclimatise

Question 32

pathophysiology of high altitude cerebral oedema

Answer 32

cerebral vessel vasodilation in response to hypoxaemia; increased fluid leakage to cranium, compressing brain and raising intra-cranial pressure

Question 33

symptoms of high altitude cerebral oedema

Answer 33

confusion, ataxia (poor-coordination), behavioural change, hallucinations, disorientation

Question 34

consequences of high altitude cerebral oedema

Answer 34

irrational behaviour, irreversible neurologic damage, coma/death

Question 35

treatments for high altitude cerebral oedema

Answer 35

immediate descent, hyperbaric O2 therapy, dexamethasone