ventilation, perfusion & gas transport in blood Flashcards
what is ventilation ?
air getting to alveoli
what is perfusion?
local blood flow
what happens to perfusion and ventilation as you move from the top of the lungs to the bottom?
they both decrease
where is the lung highly perfused?
the base
is pulmonary arterial pressure high or low and what are the systolic and diastolic values?
pulmonary arterial pressure is low
systolic- 25mmHg
diastolic- 8mmHg
what mismatch takes place in the apex?
ventilation>perfusion
ratio more than 1
leads to the opposite of a shunt (alveolar dead space)
alveolar PO2 rises- pulmonary vasodilation
PCO2 falls- bronchial constriction
what mismatch takes place in the base?
Ventilation
what is alveolar dead space?
alveoli that are ventilated but not diffused
what is physiologic dead space?
alveolar + anatomical dead space
what is a shunt?
when blood is moved from the right side of the heart to the left side without undergoing gas exchange
what is the role of respiratory sinus arrhythmia?
to minimise ventilation:perfusion mismatch during the breath cycle.
what are the 2 forms in which oxygen travels in the blood?
in solution in plasma 3ml/L
bound to haemoglobin 197ml
what % of CO2 is transported in plasma and what % in haemoglobin?
77% in solution in plasma
23% stored within haemoglobin
what is the role of haemoglobin in the transport of O2 in the blood?
binds to oxygen
why does the shape of the oxyhaemoglobin dissociation curve aid O2 loading in the lungs and unloading in the tissues?
what is the main determinant of how much oxygen binds to haemoglobin ?
PaO2 (partial arterial pressure of O2)
what is the main determinant of total oxygen content?
How much oxygen binds to haemoglobin, because 97% of oxygen carried in the blood is bound to haemoglobin
How much oxygen can bind to haemoglobin is directly determined by…
PaO2, number of red blood cells and amount of haemoglobin in each
How much oxygen can bind to haemoglobin is further influenced by…
PaCO2, body temperature, plasma pH and levels of 2,3 DPG.
what is anaemia?
any conditions which results in a decrease in the O2 carrying capacity of the blood
eg. iron deficiency, haemorrhage, vitamin B12 deficiency
what would happen to PO2 in anaemia?
nothing PO2 is normal despite total blood O2 being low
what are the factors that affect the dissociation curve?
- affinity of haemoglobin for O2 is decreased by a decrease in pH, or/and increase in PCO2, or temperature
- a rise in pH, or fall in PCO2, or temperature increases affinity or haemoglobin for O2
- affinity of haemoglobin for O2 decreases by binding of 2-3-DPG
what increases in situations associated with low O2 supply and helps maintain O2 release in tissues?
2-3-DPG
what does carbon monoxide form when it binds to haemoglobin?
carboxyhemoglobin which has an affinity 250 times greater than O2, this is problematic once dissolved in circulation
