RMS Quiz 2 - Ventilation Perfusion Flashcards
(24 cards)
What does ventilation perfusion refer to
The relationship between the airflow in the alveoli and the bloodlfow in the pulmonary circulation
What is the normal rate of ventilation and perfusion
5L/min
What is V/Q
The ratio of ventilation (airflow) and perfusion (blood flow)
What’s a normal V/Q
0.8- 1 (sometimes blood flow can be greater than airflow)
What does a
1) low V/Q value mean
2) a high V/Q value mean
1) ventilation is low, perfusion is normal
2) ventilation is normal, perfusion is low
What could be a cause of low V/Q and what does it mean
= ventilation is poor and perfusion is fine
Meaning o2 conc in the alveoli is insufficient for normal diffusion
This happens in pneumonia
What could be a cause of high V/Q and what does it mean
= low perfusion and normal ventilation
Occurs in pulmonary embolism or any disorder that reduces cardiac output
Do high V/Q areas have high O2 content once saturated
No- because although there’s enough oxygen there isn’t sufficient blood flow and therefore haemoglobin to carry all the oxygen once it’s saturated
Do high V/Q areas compensate for low V/Q areas
No because once the haemoglobin is fully saturated it can’t carry more oxygen to the low V/Q areas and most of the pulmonary blood flow goes to low V/Q areas
Why does most of the pulmonary flow go to low V/Q areas
These areas have low oxygen levels and normal blood flow
Gravity mainly is the reason why the blood tends to go to these areas and that’s why they may become low V/Q because the get lots of blood and not enough oxygen to MATCH IT
Is increased ventilation sufficient to increase o2 content
No it mainly reduces co2 content but isn’t sufficient alone to increase o2
What is a circulatory shunt
When blood BYPASSES the lung without picking up oxygen, meaning this deoxygenated blood mixes with oxygenated blood, lowering the overall oxygen levels in the body
What is a right-to-left shunt
When the coronary veins (deoxygenated blood) on the right drain directly into the left ventricle (oxygenated blood) via the thebesian vein
Hence right to left shunt
What conditions can left to right shunts occur in
1) collapsed lung (no gas exchange & perfusion is wasted)
2) pneumonia (infection) causing oedema so no gas exchange and perfusion is wasted
3) fallot’s tetralogy = hole in the heart so deoxygenated blood flows into the aorta
What’s a left-to-right stunt
When already oxygenated blood joins deoxygenated blood and travels to the lungs - thus does not cause cyanosis
What do shunts cause
They stimulate chemoreceptors
Stimulate ventilation (just causes more co2 removal) resulting in low PaO2 (arterial partial pressure of oxygen) and low or normal PaCO2
What is the effects of gravity on ventilation
Ventilation is greater at the base than the apex due to gravity pulling downwards
Effects of gravity on perfusion
Gravity pulls blood downwards so blood flow is greater at the base of the lungs compared to the apex
What is more effected by gravity, ventilation or perfusion and what does this cause
Perfusion - mismatch at the lungs
What is the mismatch at the lungs and how is it sorted
Base of the lungs low V/Q and the apex = high V/Q
Solution =
Hypoxic vasoconstriction pulmonary vessels = this helps reduce blood flow to poorly ventilated areas and divert it to well ventilated areas
What are symptoms of ventilation perfusion mismatch
Fatigue, headache, blue skin and rapid breathing
What is hyperventilation and its effects
Over-ventilation in proportion to metabolism (u don’t need to breath that much)
Leads to decreased PCO2 , reducing the conc of H+ ions leading to respiratory alkalosis and hypocapnia
This leads to vasoconstriction which reduces blood flow to the brain and can cause headaches, dizziness and fainting AND causes the Bohr effect - harder for haemoglobin to release o2 to the tissues
It can also cause increased Ca2+ stimulation leading to spasms
What is hypoventilation and its effects
Under ventilation in proportion to metabolism
Leads to increased PaCO2 which causes vasodilation (red flushed skin), hypercapnia, respiratory acidosis this can all cause CNS depression, confusion, coma and death <3
