Diffusion Flashcards
What five things determine the diffusion across the blood-gas barrier?
- Pressure difference (driving force)
- Surface area of barrier
- 1/thickness of barrier
- 1/(molecular weight of gas)
- Solubility of gas in barrier
What is diffusion capacity defined as?
[Volume of CO transferred]/[Partial pressure difference]
What is Barrier Resistance?
Defined as: [Partial Pressure Difference]/[volume of gas transferred (R=P/F (flow))]
What is diffusion?
The process by which O2 (or other gases) move from higher to lower pressure.
How does O2 and CO2 move in the blood and alveoli?
Through the process of diffusion:
- O2 goes from alveoli to blood
- CO2 goes from blood to alveoli
How does Diffusion relate to surface area?
Diffusion is proportional to surface area.
How does Diffusion related to barrier thickness?
Diffusion is inversely proportional to barrier thickness.
What is the surface area of the lungs?
50-100 m^2
What is the thickness of the lungs?
Incredibly small (less than 1 um)
What is the driving force for diffusion?
Pressure differences! (Partial pressure differences)
What two other factors can influence diffusion?
- Molecular weight
2. Solubility
How does molecular weight influence diffusion?
Bigger things don’t diffuse as well!
How does solubility influence diffusion?
- More soluble things diffuse better
- CO2 diffuses better than O2 (20 x better)
What are Diffusion Limited Processes?
- Reaction of CO (carbon monoxide) with blood
- Oxygen transfer can be diffusion limited (but only in pulmonary diseases)
- Determined by different solubilities in blood and the blood-gas barrier
What causes oxygen transfer to be diffusion limited in pulmonary diseases?
Need increased barrier to diffusion such as thickening of the blood-gas barrier
