Gas Exchange And Oxygen In The Blood Flashcards
Why would diffuse lung fibrosis reduce paO2 but conserve paCO2?
Length of diffusion pathway is increased, so less oxygen is able to diffuse into the blood in the given time. As carbon dioxide diffuses 20x more readily into blood it can still be excreted in the given time and therefore its partial pressure is conserved
What adaptations are seen in people living in high oxygen environments?
Increased Hb levels due to EPO secretion
Dense capillary beds - reduce diffusion pathway length
Increased levels of 2,3 BPG
What effects does carbon monoxide have on oxygen dissociation?
Binds to haemoglobin tightly itself and promotes the relaxed state, making oxygen less likely to dissociate from haemoglobin
What 3 things promote the tense state of haemoglobin?
Increase in temperature
Decrease in pH
Increase in 2,3 BPG levels
What 3 things promote the relaxed state of haemaglobin?
Decreased temperature
Increased pH
Binding of carbon monoxide
What is the overall effect of hyperventilation on paO2 and paCO2?
pO2 increases minimally as most of oxygen is bound to haemoglobin in the blood. pCO2 decreases - may cause hypocapnea
What is shunt?
Perfusion with no ventilation
What is dead space?
Areas of ventilation but no perfusion
What are the limitations of pulse oximetry?
May be unable to differentiate methaemaglobins or Carboxyhaemoglobin
Does not provide total amount of Hb
Less effective for patients with dark skin
What are the limitations of arterial blood gas?
Very painful
Requires specialist technique
Doesn’t detect CO
What phenomenon explains the sigmoidal shape of the haemoglobin-oxygen curve?
Positive cooperation - when one oxygen molecule binds to haemaglobin, molecular rearrangement of haemaglobin allows further oxygen molecules to bind more easily
What are the typical values of paO2 and paCO2?
paO2 - 10.5-13.5kPa
paCO2 - 4.7-6kPa
What is hypoxaemia?
What is hypoxia?
Low paO2 in arterial blood
Low oxygen levels in tissue
Where would you see hypoxaemia but not hypoxia?
Where would you see hypoxia but not hypoxaemia?
People who live in high altitudes
Anaemia
What factors affect the rate of gas diffusion?
Surface area available for diffusion
Length of diffusion pathway
Diffusion coefficient of the gas
