PULMONARY 05: DIFFUSION/PERFUSION Flashcards
The process of diffusion follows basic gas laws. What does this mean facilitates transfer of gases across membranes in the diffusion process in this case?
- ) Large surface area of alveoli
- ) Short distance to travel (0.2-0.5um)
- ) Gases have advantageous diffusion properties (this seems like a copout but whatever)
Slide 5 in lecture
How does the structure of RBC’s and capillaries help facilitate gas exchange? (2 reasons i’m thinking of, 1 structural and 1 temporal)
Only one RBC can fit through a capillary at a time, so all around the RBC gas exchange can occur.
Capillaries are short, but the RBC passage time (<1s) is long enough to facilitate exchange of gasses.
Slide 6 in lecture
How many barriers does gas have to cross to get between the alveoli and capillaries?
12
Order of barriers gasses must go through to get FROM alveoli TO lung capillaries
- ) Across alveolar air space
- ) Across alveolar water space
- ) From alveolar water interface into Type I epithelial cell
- ) Across this cell
- ) From type I epithelial cell into interstitial space (with ECM matrix)
- ) Across this matrix
- ) From ECM matrix into capillary endothelial cell
- ) Across this cell
- ) Across PM of endothelial cell into blood plasma
- ) Across blood plasma
- ) Out of blood plasma and across RBC PM
- ) Through PM of RBC to bind to Hgb
Slide 7
Fick’s law dictates that the flow of gas is proportional to what?
Area, the gas’s diffusion constant, and the driving pressure force (deltaP)
Slide 9
Fick’s law dictates that the flow of gas is inversely proportional to what?
The thickness of the barrier
How does Fick’s law dictate the flow of gas will be affected by pulmonary edema?
In pulmonary edema there is a much bigger barrier; thus gas flow will be impeded and diffusion decreased.
How does Fick’s law dictate the diffusion of a gas will be affected by a collapsed lung?
If you collapse a lung, the area of the system is immensely reduced, thus diffusion is immensely reduced or even eliminated
How does Fick’s law dictate that being at high altitude will affect diffusion?
At high altitude, you’re starting at a lower pressure of gas X, which means there is a reduced driving force. Therefore, you decrease diffusion.
What does graham’s law say is proportional to the rate of diffusion?
The solubility coefficient of the gas
slide 10
what does graham’s law dictate is inversely proportional to the rate of diffusion
The square root of the molecular weight of the gas
Which is better at diffusing, CO2 or O2?
CO2. But O2 will diffuse readily under normal conditions
Slide 10
Why do we assume that PACo2 and PaCO2 are the same?
Because CO2 is so good at diffusing
Slide 10
What does it mean if something is diffusion limited?
The amount of molecule X brought into circulation is limited by diffusion across the alveolar membrane
Slide 14
What are two reasons diffusion limitation might result in a low diffusion rate?
- ) Molecule X cannot diffuse across the barrier
- ) Molecule X is converted into something else as soon as it is brought into the blood , therefore it no longer counts toward the partial pressure (it is no longer dissolved as its own thing) - This gets back to Henry’s law where the partial pressure of a gas above and its concentration in solution are proportional
Slide 14, slide 15 for henry’s law
What is perfusion limited gas transfer?
The amount of molecule X carried into circulation is limited by the rate of perfusion (aka, the rate of blood going through pulmonary capillaries)
Slide 17
Insoluble gasses like N2O are __(diffusion/perfusion)__ limited; soluble gasses like carbon monoxide are normally speaking __(diffusion/perfusion)__ limited
Perfusion limited
Diffusion limited
slide 19
Under normal conditions, ppO2 in alveoli does what? How does this interact with normal perfusion an result in a normal kind of gas exchange?
It climbs quickly. This means there is a strong driving force which quickly equilibrates. This means that of the ~1s there is a rbc in a capillary, 1/2 of it is extra time , aka “Diffusion reserve time”
Slide 20
How does exercise alter the perfusion of alveoli?
RBC’s are moving much faster through the system, so transit time is decreased. There is still plenty of time , in a normal individual, to transmit oxygen, but if someone is sick and already experiencing other pulmonary/circulatory issues this could potentially be a noticable change.
How does edema alter oxygen uptake along the pulmonary capillary
In mild edema, the slope of the curve will change due to thickening of the barrier for O2 to travel (slows rate of diffusion). During exercise now, patient does not have a goo reserve time so you see this limitation in oxygen diffusion. This becoms more pronounced as the edema becomes more severe.
Slide 20
In normal conditions, oxygen is __(diffusion/perfusion)__ limited. In many pathologies such as edema, and often combining with exercise, oxygen is now __(diffusion/perfusion)__ limited.
Perfusion;
diffusion
Slide 20
How do we measure the diffusion properties of someone’s lungs?
CO.
Because CO is not supposed to be in the lungs, we assume there is nothing in arterial system. this is a huge driving force.
Therefore, the single breath dilute CO test (combined with helium as a tracer to nromalize volume) can be sued to see how much is getting into blood.
Breathe in CO, hold 10s, then breathe back out. During that time, the CO will cross the barrier (helium will not) to get into bloo. THen breathe out and see how much CO and He come out. If smeone has a diffusion limited pathology, the amount that crosses is reduced leaving more in the lungs.
Slides 22, 23
O2 and CO2 are normally (diffusion/perfusion) limited
Perfusion (slide 25)
Under what conditions will O2 become diffusion limited?
Under extreme conditions (altitude, extreme exercise), or disease (fibrosis, edema)
slide 25
