Ventilation Perfusion Relationship Flashcards
ventilation?
the provision of gas to an area (ventilate)
perfusion?
the provision of blood to an area (perfuse)
what is a lung a collection of?
of single units (alveolus) that allow for the exchange of gases
in order for gas exchange to occur, what must occur?
ventilation and perfusion
ideally, ventilation and perfusion should be?
they should be matched - 1:1
ventilation of lung must occur in all the areas that is being perfused
perfusion of lung must occur in all the areas that is being ventilated
V?
ventilation
Q?
perfusion
what can change VQ?
it can change depending on anatomical location of lung in relation to the heart - gravity etc.
VQ ratio is normally?
0.8 to 1 - so not perfect but it is good enough
the ratio of ventilation to perfusion (V/Q) is the critical factor governing gas exchange…
regions of HIGH ventilation should have HIGH blood flow
and
regions of LOW ventilation should have LOW blood flow
disruption in the VQ ratio is the principal cause of what?
arterial hypoxia leading to clinical signs of hypoxia
what is alveolar oxygen determined by?
amount of oxygen entering the alveoli
amount of oxygen being removed by capillary blood flow
alveolar carbon dioxide is determined by?
determined by amount of carbon dioxide that diffuses into the alveoli from the capillary blood
amount of carbon dioxide being removed from the alveoli through alveolar ventilation
effect on oxygen as ventilation increases?
more oxygen enters the alveolus (partial pressure rises)
effect on oxygen as ventilation decreases?
less oxygen enters (partial pressure falls)
effect on oxygen as perfusion increases?
more oxygen leaves (partial pressure falls)
effect on oxygen as perfusion decreases?
less oxygen leaves (partial pressure rises)
effect on carbon dioxide as ventilation decreases?
less carbon dioxide is eliminated (partial pressure rises)
effect on carbon dioxide as ventilation increases?
more carbon dioxide is eliminated (partial pressure falls)
effect on carbon dioxide as perfusion decreases?
less carbon dioxide is returned for elimination (partial pressure falls)
effect on carbon dioxide as perfusion increases?
more carbon dioxide is returned for elimination (partial pressure rises)
how can VQ be increased?
overventilation or underperfusion
how can VQ be decreased?
underventilation or overperfusion
increased VQ means?
means increased in alveolar dead space (Vd) thus ventilation is wasted
what is Vd? (d should be a small capital letter)
Deadspace ventilation: volume ventilated but not exchanging with pulmonary capillary blood
wasted ventilation?
cannot move air in or out due to blockage but blood still moves past it - shunting (when Q is larger than V)
perfusion exceeds ventilation results in?
shunted blood
ventilation exceeds perfusion results in?
deadspace ventilation
normal?
when ventilation matches perfusion
decreased VQ means there is…
shunting (no gaseous exchange occurs)
when there is zero ventilation?
no exchange at all - known as true shunt - ventricular septal defect, atelectasis (alveolar collapse) etc.
what is hypoxic pulmonary vasoconstriction?
a physiological reflex mechanism where the pulmonary arteries constrict in the presence of hypoxia
why does vasodilation in hypoxia occur?
in order to supply more blood
what is the end aim for HPV? (hypoxic pulmonary vasoconstriction
to normalise VQ ratio
redistribution of blood from poorly ventilated areas to areas that are well ventilated
responsible for maintaining the ventilation-perfusion ratio during localised alveolar hypoxia
