chapter 3 diffusion Flashcards
What is Ficks law of diffusion?
Vgas proportional to A/T * D * (P1-P2)
A = area T = thickness D = solubility / sq root MW
MW: heavier molecules move slower and hit membrane less. Essentially Density.
solubility: captures the size of the particle
Give example of a gas that is
- diffusion limited
- perfusion limited
- diffusion: CO
2. perfusion: N2O, O2
In what circumstances can O2 become diffusion limited
exercise diffusion barrier (lung disease) high altitude (alveolar hypoxia)
What is the equation for diffusing capacity?
.
DL= VCO / PaCO
What is normal diffusing capacity?
25 ml/min/mmHg
what is the effect of exercise on diffusing capacity?
increases bc of recruitment and distension
What are the stages of uptake for O2 or CO?
What is the equation for this?
- Diffusion of O2 through the blood-gas barrier (including plasma and red cell interior)
- Reaction of O2 with hemoglobin
This produces an overall “diffusion” resistance
1/DL = 1/DM + 1/(theta*VC)
- theta is the reaction rate with Hb
- Vc is capillary blood volume
The resistance to the uptake of O2 attributable to reaction rate is probably about same as that due to diffusion across blood-gas barrier
What is transfer factor?
European term for diffusing capacity
diffusion does not solely reflect diffusion properties of lung. Also dependent on volume of blood in pulmonary capillaries
How does CO2 transfer compare to O2 transfer?
CO2 transfer is 20x faster than O2 (more soluble)
D = solubility / sq rt MW
How does increased FiO2 affect DLCO?
Increased FiO2 decreases DLCO bc O2 competes with CO for binding with Hb
What is the equation for DLCO?
.
DLCO = VCO/PACO
This is derived from Fick equation
Vgas = A/T * D (P1-P2)
Vgas = DLCO (P1-P2)
Because P2 is infinitely small it is dropped from the equation
