hypoxia Flashcards
what does hypoxia describe?
specific environment
Specifically the PO2 in that environment
what does hypoxaemia describe?
blood environment
Specifically the PaO2
under 8kPa
what is ischaemia?
when tissues receive inadequate oxygen
what can put the body under hypoxic stress and what happens?
- Altitude, disease can put the body under hypoxic stress
review of oxygen transport?
- 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
what is the oxygen cascade?
- this describes the decreasing oxygen tension from inspired air to respiring cells
what are the factors that the diffusing air is proportional to?
- SA for gas exchange
- diffusion constant
- diffusion gradient
why does the oxygen tension decrease?
- 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
how is oxygen transported?
dissolved 2%
bound 98%
what factors affect the oxygen cascade?
- 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)
what energy is used when we exercise?
- 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
how does oxygen delivery change when one exercises?
- you increase your energy demand
- increase ventilation
- increase cardiac output
- increase oxygen delivery
how much O2 do we need for sub maximal exercise ?
40 L/min
what is EPOC?
this is excess post exercise oxygen consumption?
trying to reverse the consequences of an oxygen deficit
what is the ventilatory response to exercise?
- 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
what are the 5 challenges of altitude?
- hypoxia
- thermal stress
- solar radiation
- hydration
- dangerous
what is accommodation
- acute response to this kind of stress
what is acclimatisation?
- when the physiology gets more efficient so that you can get as much air out as possible
what happens during acclimatisation?
- 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
what is hypobaric hypoxia?
- when low PaO2 stimulates ventilation to increase PaO2
what are the developmental adaptions with high altitude?
- 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
what is chronic mountain sickness?
- 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
what is acute mountain sickness?
- maladaption to the high altitude environment
- mild cerebral oedema
- nausea and vomiting
- it might turn into HACE or HAPE
what is high altitude pulmonary oedema ? HAPE
- vasoconstriction of pulmonary vessels in result to hypoxia
- leakage from capillaries
- breathlessness, cough, bloody sputum
what is high altitude cerebral oedema? HACE
- vasodilation of the vessels
- in response to hypoxaemia
- causes ataxia
- disorientation behaviour change confusion
- immediate descent
what is respiratory failure?
- ineffective inability to exchange gas between the lungs and the blood
- there are 2 main types
what is type 1 resp failure?
what is type 2 resp failure?
- T1: hypoxic resp failure O2 is too low - T2: hypercapnic resp failure Co2 is too high
what causes T1 and T2?
- T1:
ventilation or perfusion mismatch - T2:
typically hypoventilated lungs
