PULMONARY 05: DIFFUSION/PERFUSION

Question 1

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?

Answer 1

1. ) Large surface area of alveoli
2. ) Short distance to travel (0.2-0.5um)
3. ) Gases have advantageous diffusion properties (this seems like a copout but whatever)

Slide 5 in lecture

Question 2

How does the structure of RBC’s and capillaries help facilitate gas exchange? (2 reasons i’m thinking of, 1 structural and 1 temporal)

Answer 2

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

Question 3

How many barriers does gas have to cross to get between the alveoli and capillaries?

Answer 3

12

Question 4

Order of barriers gasses must go through to get FROM alveoli TO lung capillaries

Answer 4

1. ) Across alveolar air space
2. ) Across alveolar water space
3. ) From alveolar water interface into Type I epithelial cell
4. ) Across this cell
5. ) From type I epithelial cell into interstitial space (with ECM matrix)
6. ) Across this matrix
7. ) From ECM matrix into capillary endothelial cell
8. ) Across this cell
9. ) Across PM of endothelial cell into blood plasma
10. ) Across blood plasma
11. ) Out of blood plasma and across RBC PM
12. ) Through PM of RBC to bind to Hgb

Slide 7

Question 5

Fick’s law dictates that the flow of gas is proportional to what?

Answer 5

Area, the gas’s diffusion constant, and the driving pressure force (deltaP)

Slide 9

Question 6

Fick’s law dictates that the flow of gas is inversely proportional to what?

Answer 6

The thickness of the barrier

Question 7

How does Fick’s law dictate the flow of gas will be affected by pulmonary edema?

Answer 7

In pulmonary edema there is a much bigger barrier; thus gas flow will be impeded and diffusion decreased.

Question 8

How does Fick’s law dictate the diffusion of a gas will be affected by a collapsed lung?

Answer 8

If you collapse a lung, the area of the system is immensely reduced, thus diffusion is immensely reduced or even eliminated

Question 9

How does Fick’s law dictate that being at high altitude will affect diffusion?

Answer 9

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.

Question 10

What does graham’s law say is proportional to the rate of diffusion?

Answer 10

The solubility coefficient of the gas

slide 10

Question 11

what does graham’s law dictate is inversely proportional to the rate of diffusion

Answer 11

The square root of the molecular weight of the gas

Question 12

Which is better at diffusing, CO2 or O2?

Answer 12

CO2. But O2 will diffuse readily under normal conditions

Slide 10

Question 13

Why do we assume that PACo2 and PaCO2 are the same?

Answer 13

Because CO2 is so good at diffusing

Slide 10

Question 14

What does it mean if something is diffusion limited?

Answer 14

The amount of molecule X brought into circulation is limited by diffusion across the alveolar membrane
Slide 14

Question 15

What are two reasons diffusion limitation might result in a low diffusion rate?

Answer 15

1. ) Molecule X cannot diffuse across the barrier
2. ) 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

Question 16

What is perfusion limited gas transfer?

Answer 16

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

Question 17

Insoluble gasses like N2O are __(diffusion/perfusion)__ limited; soluble gasses like carbon monoxide are normally speaking __(diffusion/perfusion)__ limited

Answer 17

Perfusion limited

Diffusion limited

slide 19

Question 18

Under normal conditions, ppO2 in alveoli does what? How does this interact with normal perfusion an result in a normal kind of gas exchange?

Answer 18

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

Question 19

How does exercise alter the perfusion of alveoli?

Answer 19

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.

Question 20

How does edema alter oxygen uptake along the pulmonary capillary

Answer 20

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

Question 21

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.

Answer 21

Perfusion;
diffusion
Slide 20

Question 22

How do we measure the diffusion properties of someone’s lungs?

Answer 22

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

Question 23

O2 and CO2 are normally (diffusion/perfusion) limited

Answer 23

Perfusion (slide 25)

Question 24

Under what conditions will O2 become diffusion limited?

Answer 24

Under extreme conditions (altitude, extreme exercise), or disease (fibrosis, edema)

slide 25

Question 25

How much blood is carried in the pulmonary arteries at any point in time

Answer 25

500mL (total CO)

slide 28

Question 26

How much blood is in alveolar capillary network?

Answer 26

~70mL but you can increase that 2x or 3x in exercise

Question 27

The pulmonary capillaries have more/less resistance compared to systemic capillaries

Answer 27

Typically less

slide 29

Question 28

The pulmonary system has what kind of driving pressure compared to the systemic system (circulatory)?

Answer 28

Reduced driving pressure gradient (slide 29)

Question 29

Factors that influence lung perfusion (4)

Answer 29

Pulmonary vascular resistance
Gravity
Alveolar pressure
Arterial-venous pressure gradient

Slide 30

Question 30

How does pulmonary vascular resistance impact lung perfusion?

Answer 30

Alters the deltaP (driving force of flow).

Pulmonary vessels are shorter and wider than systemic, have less smooth muscle, and lower resting tone.

Slide 31

Question 31

PVR __(increases/decreases)__ with __(Increasing/decreasing)__ vascular pressures

Answer 31

Increases;
Decreases

Or vice vesa
Decreases
increasing

Slide 32

Question 32

As we see an increase in pressure, there is a drop in resistance. Why?

Answer 32

1. Recruitment and distention (vessels that are normally closed are recruited and opened due to the increasing pressure)
2. ) Recruitment via vessels open but having no flow/negligible low flow in system have increased flow due to increased pressure gradient

3.) Vessels that are already opened are distended further open.
slide 32

Question 33

kinds of pressures around pulmonary blood vessels

Answer 33

Extra alveolar pressures experience lot of tissue pressure

Alveolar pressures experience pressure from expanding aveoli
slide 33

Question 34

What changes PVR during normal breathing?

Answer 34

Lung volume

Slide 34

Question 35

What is the effect of gravity on distribution of blood flow?

Answer 35

Gravity means more blood go to bottom easier and that blood flow depends on posture
slide 36

Question 36

How can you measure the effect of blood flow in someone’s pulmonary system?

Answer 36

Radiation into lungs and you measure with scintillation counters on the back to see where radioactivity is
slide 36

Question 37

Ventilation is highest in the (apex, base) of lungs

Answer 37

Base
slide 37
also see slide on pulm4 about this

Question 38

Hypoxic pulmonary vasoconstriction shifts blood in what way?

Answer 38

From poorly ventilated areas to well ventilated areas

Question 39

During what moment in someone’s life is hypoxic pulmonary vasoconstriction critical to have normal breathing?

Answer 39

Right after birth

Question 40

Fluid movement across capillary is governed by a balance of what forces?

Answer 40

hydrostatic, oncotic

Question 41

If drainage of capillaries exceeds maximal lymph flow, what resuls?

Answer 41

Edema

Question 42

What kind of heart failure results in pulmonary edema?

Answer 42

LV HF