Unit 2, L5 Diffusion and Perfusion Flashcards
Transfer of gas across the blood gas barrier occurs by what
Diffusion
What factors facilitate gas diffusion in the respiratory system?
Large surface area, short distances, and gases with advantageous diffusion properties
Capillary diameter value
< 10 uM
Erythrocyte diameter
7 um
Erythrocytes in the capillaries
Pass through capillaries in single file, and the average transit time is < 1 second
The path an O2 molecule takes from alveoli to hemoglobin
Starts in the alveolar air, then diffuses across into the water layer. From there, it diffuses across the first membrane of alveolar type I epithelial cells, then diffuses into the inside of the type I epithelial cells, then diffuses out of those cells into the interstitial space with matrix, then diffuses through the first membrane layer of the pulmonary capillary endothelial cell, then diffuses into the inside of the capillary endothelial cell, then diffuses out of that cell and into the blood plasma, then diffuses across the membrane of the RBC, and finally diffuses into the cytoplasm of the RBC
Fick’s law for diffusion through tissue
The amount of gas transferred is proportional to the area (A), a diffusion constant, and the difference in partial pressure. The amount of gas transferred is indirect proportional to the thickness (T)
How would pulmonary edema effect diffusion through tissue
A mild pulmonary edema would increase the amount of fluid at th ebarrier, thicken the barrier, and decrease diffusion. A massive pulmonary edema would lose oxygen in the alveolar space and drop the driving force
How would a collapsed lung effect the diffusion of gas through tissue
It would completely eliminate the area, so there would be no diffusion
How would high altitude effect diffusion of gas through tissue
Lower total pressure, lower oxygen getting into alveoli, so dropping partial pressure of O2, lower driving pressure
Diffusion through tissue with Graham’s law
Rate of diffusion is proportional to solubility coefficient of gas over square root of molecular weight
Define diffusion-limited
The amount of molecule X carried into circulation is limited by the diffusion across the alveolar membrane
With a diffusion limited molecule, what is the driving force like
The driving force will always be higher than the rate at which the molecules can pass through the barrier
Perfusion limited definition
The amount of molecule X carried into circulation is limited by the rate of perfusion (blood flow through pulmonary capillaries)
Would diffusion or perfusion limited samples have slow equilibration
Diffusion limited would have slow equilibration
Would diffusion or perfusion limited samples have fast equilibration
Perfusion-limited would have fast equilibriation
Insoluble gasses, such as N2O, is perfusion or diffusion limited
Perfusion limited, as these chemicals do not combine with proteins, so they equilibrate rapidly and the gas transfer is limited by the amount of blood perfusing the alveolus
Soluble gases, such as CO, are perfusion or diffusion limited?
Diffusion limited. CO diffuses rapidly into erythrocytes and has high affinity for hemoglobin, with no or little increase in partial pressure
How do we measure the diffusion properties of a patient’s lungs?
Modification of Fick’s Law and Carbon Monoxide
CO in capillary blood under normal condition should be what value
0
How do you do the measurement of diffusion capacity?
Single breath of carbon monoxide. Person will breathe CO, hold for 10 seconds, then breathe back out. Look at concentration of either CO or the tracer gas that comes back out. If the patient has a diffusion capacity problem, line will go up as CO goes it, sit there and not diffuse, then come back out when they breathe out
Pulmonary arteries are the only arteries in the body that carry ____________
Deoxygenated blood
Total blood volume of pulmonary arteries
500 mL
In the alveolar capillary network, what is the volume under resting conditions
70 mL
