Gas Exchange in the Lung Flashcards
After you exhale, what is the volume of air in the alveoli, and what is the volume in the dead space?
Alveoli - 2350ml.
Dead space - 150ml.
How much atmospheric air is added when you inspire?
350ml.
What is hypoxaemia?
Low PO2.
When partial pressure of O2 falls below 10 kPa.
What level of O2 saturation does O2 have to be below for one to have hypoxaemia?
<94%.
What is the normal range of PaCo2?
4.9 - 6.1 kPa.
Describe type 1 and type 2 respiratory failures.
Type 1 - CO2 levels ok, but O2 levels are bad - hypoxaemic.
Type 2 - Patient is hypoxaemic and hypercapnic.
What are the causes of hypoxaemia?
Hypoventilation.
Diffusion defects.
VQ mismatch.
Shunt (bad VQ mismatch).
What is hypoventilation?
Not breathing enough - CO2 levels rise in blood.
Only cause of hypercapnia.
Could be seen in obesity - difficult to expand chest.
Seen in sleep apnoea - intermittent airway obstruction.
Drugs // stroke - both can affect central control of breathing.
Neuromuscular disease - makes breathing difficult.
What is Fick’s Law of Diffusion?
There’s increased diffusion if there’s a greater concentration gradient, higher solubility, decreased molecular size and increased surface area.
How do diffusion defects cause hypoxaemia?
Increased thickness - e.g oedema, fibrosis.
SA decreased in emphysema.
Concentration gradient affected - ventilation problem.
What do V and Q stand for in VQ mismatch?
V - ventilation.
Q - Blood flow - perfusion.
When can you expect dyspnoea (breathlessness)?
When rate of alveolar ventilation to blood flow is not 1..
How can you confirm where lung ventilation and blood flow in the lungs are?
Ventilation - breathe in radioactive air.
Blood flow - radioactive substance in the blood.
What is VQ mismatch?
Not a complete blockage, but obstruction to air flow in the lungs.
What is a shunt?
When something is completely blocking airway into the lungs.
What will supplying more oxygen do to someone with a shunt?
Nothing - one side won’t be able to receive it at all, and the other will already be fully saturated.
What causes a shunt?
Oedema.
Pneumonia.
Developmental problem - e.g with the foramen ovale or ductus arteriousus.
What is expiratory exchange ratio, and what is the normal value?
Measure of how much CO2 you’re producing compared to how much O2 you’re consuming.
Normal value - 0.8.
What does the alveolar gas equation tell you?
Tells you what PAO2 based on PaCO2.
How do the lungs cope with VQ mismatch?
Carry out hypoxic vasoconstriction.
This is where blood vessels in the lungs where ventilation is poor sense that there’s little oxygen. They constrict and divert blood away to a different area.
In COPD/fibrosis, the entire lung is always hypoxic, so there’s constant hypoxic vasoconstriction.
This causes major back-pressure, and the right heart will eventually fail.
