hypoxia

Question 1

what does hypoxia describe?

Answer 1

specific environment

Specifically the PO2 in that environment

Question 2

what does hypoxaemia describe?

Answer 2

blood environment

Specifically the PaO2

under 8kPa

Question 3

what is ischaemia?

Answer 3

when tissues receive inadequate oxygen

Question 4

what can put the body under hypoxic stress and what happens?

Answer 4

• Altitude, disease can put the body under hypoxic stress

Question 5

review of oxygen transport?

Answer 5

• begin with ambient air with pp of 21.3kPa
• as altitude decreases the barometric pressure and partial pressure decreases
• this is due to daltons law to 13.5 kpa
• the air is then humidified and mixed
• the pp is the same in the alveolar capillaries due to the direct diffusion
• the blood reaches the gas exchange surface at 5.3kPa

Question 6

what is the oxygen cascade?

Answer 6

• this describes the decreasing oxygen tension from inspired air to respiring cells

Question 7

what are the factors that the diffusing air is proportional to?

Answer 7

• SA for gas exchange
• diffusion constant
• diffusion gradient

Question 8

why does the oxygen tension decrease?

Answer 8

• you start with 21.3kPa
• humidification decreases the oxygen a little bit
• mixing also decreases the oxygen a little bit
• there should then be no change between the alveolar air and post alveolar air
• there is then a slight decrease between post alveolar capillaries and arteries due to bronchial drainage
• the artery PO2 is 13.3.kPa
• then vein PO2 is 5.3KPa

Question 9

how is oxygen transported?

Answer 9

dissolved 2%

bound 98%

Question 10

what factors affect the oxygen cascade?

Answer 10

• alveolar ventilation
• ventilation
  ( unventilated alveoli will result in no change in PO2)

( not perfused or hyper perfused airways also result in ineffective gas exchange)

• diffusion capacity
  ( diseases affecting parenchyma can become thickened and less conductive to exhange)
• cardiac output
  ( increase CO means increased blood flow so more oxygenation)

Question 11

what energy is used when we exercise?

Answer 11

• first 10 seconds uses ATP and ATP phosphocreatine system
• longer than 60 seconds = aerobic
• eventually we use anaerobic mechanisms
• produces lactic acid –> lactate - and H+
• lowers Ph and stops the glycolytic enzymes

Question 12

how does oxygen delivery change when one exercises?

Answer 12

• you increase your energy demand
• increase ventilation
• increase cardiac output
• increase oxygen delivery

Question 13

how much O2 do we need for sub maximal exercise ?

Answer 13

40 L/min

Question 14

what is EPOC?

Answer 14

this is excess post exercise oxygen consumption?

trying to reverse the consequences of an oxygen deficit

Question 15

what is the ventilatory response to exercise?

Answer 15

• the breathing rate rapidly increases
• then the breathing rate becomes stable
• it becomes stable due to the increase in tidal volume
• this is more efficient at increasing ventilation
  than increasing the respiratory rate

Question 16

what are the 5 challenges of altitude?

Answer 16

• hypoxia
• thermal stress
• solar radiation
• hydration
• dangerous

Question 17

what is accommodation

Answer 17

• acute response to this kind of stress

Question 18

what is acclimatisation?

Answer 18

• when the physiology gets more efficient so that you can get as much air out as possible

Question 19

what happens during acclimatisation?

Answer 19

• the physiology gets more efficient so you can get as much air out as possible
• during acclimatisation PaO2 falls and PaCO2 falls
• this results in renal compensation for respiratory alkalaemia
• a slow increasing ventilatory sensitivity to hypoxia

Question 20

what is hypobaric hypoxia?

Answer 20

• when low PaO2 stimulates ventilation to increase PaO2

Question 21

what are the developmental adaptions with high altitude?

Answer 21

• barrel chest
  larger set of lungs so increased SA
  more alveoli
• increased haematocrit
  more RBCs due to chronic secretion of erythropoietin
  more o2 carrying capacity of the blood
• larger heart
  pulmonary vasculature constricts in response to hypoxia
  so we need a stronger right side of the heart
• increased mitochondrial density
  greater oxygen utilisation
  means more O2 is utilised

Question 22

what is chronic mountain sickness?

Answer 22

• secondary polycythaemia in response to hypoxia
• RBCs are over produced
• increased haematocrit but also thicker blood
• this is chronic
• no medical intervention
• the sufferers need to move to lower altitudes

Question 23

what is acute mountain sickness?

Answer 23

• maladaption to the high altitude environment
• mild cerebral oedema
• nausea and vomiting
• it might turn into HACE or HAPE

Question 24

what is high altitude pulmonary oedema ? HAPE

Answer 24

• vasoconstriction of pulmonary vessels in result to hypoxia
• leakage from capillaries
• breathlessness, cough, bloody sputum

Question 25

what is high altitude cerebral oedema? HACE

Answer 25

• vasodilation of the vessels
• in response to hypoxaemia
• causes ataxia
• disorientation behaviour change confusion
• immediate descent

Question 26

what is respiratory failure?

Answer 26

• ineffective inability to exchange gas between the lungs and the blood
• there are 2 main types

Question 27

what is type 1 resp failure?

what is type 2 resp failure?

Answer 27

- T1: 
hypoxic resp failure
O2 is too low 
- T2: 
hypercapnic resp failure Co2 is too high

Question 28

what causes T1 and T2?

Answer 28

• T1:
  ventilation or perfusion mismatch
• T2:
  typically hypoventilated lungs