Hypoxia Flashcards
Hypobaric hypoxia= ?
low pressure hypoxia because even though the proportions are the same the amount of O2 is less
Hypoxia
Describes a specific environment, specifically PO2 in environment
Hypoxaemia
Describes the blood environment, specifically the PaO2
Ischaemia
Describes tissues receiving inadequate oxygen, e.g. forearm ischaemia
As a result of receiving hypoxaemic blood
Relationship between PaO2 and Age
Increase age= decrease PaO2
The O2 cascade describes?
Related to which law?
the decreasing oxygen tension from inspired air to respiring cells
O2 is most abundant when it’s in the air (keeps getting lower throughout the pathway of the body)
Fick’s law of diffusion states that flow rate is proportional to the pressure gradient
Fick’s law
What influences it?
“V Gas”= 𝐴/𝑇∙𝐷∙[𝑃1−𝑃2]
Structural diseases reduce A
Breathing hypoxic gas reduces P1-P2 gradient
Fluid in alveolar sacs increases T
Oxygen cascade summary graph draw (slide 9, lecture 15) Where is biggest proportion of O2 lost? Impact of hyperventilation? Second significant drop? Dotted lines? Why don't O2 and CO2 change by same amount?
Mixing phase is where the biggest proportion of O2 is lost
Hyperventilation (not just breathing fast) increases the partial pressure O2 gradient and CO2 gradient with means more O2 can get in which increases PO2
Second significant drop= by the tissues (but depends on what they’re doing)
Dotted lines- where O2/ CO2 may go down/up during exercise, Amount O2 changes and CO2 changes is not equal because of the sigmoid shaped curve in O2 but linear shaped curve in CO2
Factors that can impede oxygen cascade+ explanation
Alveolar ventilation
V/Q matching
V/Q matching= Ventilation/ Perfusion mismatching, e.g. if there is a blockage in an airway which prevents air from getting there but blood is coming there then it doesn’t matter how much ventilation is occurring because it wont get to the gas exchange surface.
Diffusion capacity
Diffusion capacity: could be to do with gas or membrane (if membrane thickness increases then diffusion rate decreases)
Cardiac output
Cardiac output: heart needs to be good at delivering the blood with a higher conc of o2 to the tissues otherwise the pulmonary circulation is pointless
Impact of high altitude on oxygen cascade draw?
slide 10, lecture 15
smaller bars= at a high altitude, the O2 cascade is much more shallow plus you’re probably physically exerting yourself= harder to maintain homeostasis
Changes of high altitude
Hypoxia: Much less oxygen in the ambient air
Thermal stress: Freezing cold weather (-7 °C per 1000m), High wind-chill factor
Solar radiation: Less atmospheric screening, Reflection off snow
Hydration: Water lost humidifying inspired air, Hypoxia induced diuresis
Dangerous: Windy, unstable terrain, hypoxia-induced confusion and malcoordination
Accommodation and acclimatisation to high altitude
slide 14, lecture 15
PAO2= alveolar oxygen
PaO2= arterial oxygen
Decrease in the above two recognised by peripheral chemoreceptors (usually central chemoreceptors recognise increases in CO2 so this is a different mechanism)
Increases sympathetic activation= increase ventilation= increase alveolar oxygen= increase O2 loading into blood
Sympathetic activation also increases cardiac output through increase in HR+ Stroke Volume (Q) through increases in rate of conduction through the heart
Cardiac output increases throughput in lungs+ delivery to tissues
Ventilation comes at a cost though because PaCO2 decreases= decrease ventilation even though you were solving O2 issue
Loss in CO2=increase pH= changes oxygen dissociation curve to the left which increases affinity of O2 to Hb= decrease O2 unloading
Alkalosis detected by carotid bodies from high pH (same place as peripheral chemoreceptors) leading to kidney increasing H+ and increasing HCO3- excretion, takes longer time to do this but leads to increase O2 unloading.
Low O2 detected= increase erythropoietin secretion= increase RBC production= Increase O2 loading
Other changes= Increase oxidative exzymes= increase aerobic respiration before you move to anaerobic mechanism, also increase mitochondria which both lead to increase 2,3- DPG which gives right shift to ODC because conformational change= increase O2 unloading
Acclimation meaning
Like acclimatisation but stimulated by an artificial environment (e.g. hypobaric chamber or breathing hypoxic gas)
Prophylaxis= ?
Prophylaxis for high altitude
treating something before it happens
Acetazolamide
- Carbonic anhydrase inhibitor – accelerates the slow renal compensation to hypoxia-induced hyperventilation
- directly linked to turning CO2 into H2CO3 , so inhibition reduces initial alkalotic response to low oxygen
Native highlanders have specialised anatomical and physiological adaptations:
‘Barrel chest’ – larger TLC, more alveoli and greater capillarisation, More O2 into the body
Increased haematocrit – greater oxygen carrying-capacity of the blood, More O2 carried in blood
Larger heart to pump through vasoconstricted pulmonary circulation, Greater pulmonary perfusion
Increased mitochondrial density – greater oxygen utilisation at cellular level, More O2 utilised
