Unit 2, L5 Diffusion and Perfusion

Question 1

Transfer of gas across the blood gas barrier occurs by what

Answer 1

Diffusion

Question 2

What factors facilitate gas diffusion in the respiratory system?

Answer 2

Large surface area, short distances, and gases with advantageous diffusion properties

Question 3

Capillary diameter value

Answer 3

< 10 uM

Question 4

Erythrocyte diameter

Answer 4

7 um

Question 5

Erythrocytes in the capillaries

Answer 5

Pass through capillaries in single file, and the average transit time is < 1 second

Question 6

The path an O2 molecule takes from alveoli to hemoglobin

Answer 6

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

Question 7

Fick’s law for diffusion through tissue

Answer 7

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)

Question 8

How would pulmonary edema effect diffusion through tissue

Answer 8

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

Question 9

How would a collapsed lung effect the diffusion of gas through tissue

Answer 9

It would completely eliminate the area, so there would be no diffusion

Question 10

How would high altitude effect diffusion of gas through tissue

Answer 10

Lower total pressure, lower oxygen getting into alveoli, so dropping partial pressure of O2, lower driving pressure

Question 11

Diffusion through tissue with Graham’s law

Answer 11

Rate of diffusion is proportional to solubility coefficient of gas over square root of molecular weight

Question 12

Define diffusion-limited

Answer 12

The amount of molecule X carried into circulation is limited by the diffusion across the alveolar membrane

Question 13

With a diffusion limited molecule, what is the driving force like

Answer 13

The driving force will always be higher than the rate at which the molecules can pass through the barrier

Question 14

Perfusion limited definition

Answer 14

The amount of molecule X carried into circulation is limited by the rate of perfusion (blood flow through pulmonary capillaries)

Question 15

Would diffusion or perfusion limited samples have slow equilibration

Answer 15

Diffusion limited would have slow equilibration

Question 16

Would diffusion or perfusion limited samples have fast equilibration

Answer 16

Perfusion-limited would have fast equilibriation

Question 17

Insoluble gasses, such as N2O, is perfusion or diffusion limited

Answer 17

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

Question 18

Soluble gases, such as CO, are perfusion or diffusion limited?

Answer 18

Diffusion limited. CO diffuses rapidly into erythrocytes and has high affinity for hemoglobin, with no or little increase in partial pressure

Question 19

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

Answer 19

Modification of Fick’s Law and Carbon Monoxide

Question 20

CO in capillary blood under normal condition should be what value

Answer 20

0

Question 21

How do you do the measurement of diffusion capacity?

Answer 21

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

Question 22

Pulmonary arteries are the only arteries in the body that carry ____________

Answer 22

Deoxygenated blood

Question 23

Total blood volume of pulmonary arteries

Answer 23

500 mL

Question 24

In the alveolar capillary network, what is the volume under resting conditions

Answer 24

70 mL

Question 25

In the alveolar capillary network, what is the volume during exercise

Answer 25

150-200 mL

Question 26

Characteristics of pulmonary arteries

Answer 26

Thin wall, minimal smooth muscle, 7 times more compliant than systemic arteries and easily distensible

Question 27

Factors that influence lung perfusion

Answer 27

PVR, gravity, alveolar pressure, and arterial-venous pressure gradient

Question 28

Pulmonary vascular resistance (PVR) equation

Answer 28

PVR = change in pressure (pressure in pulmonary artery - left atrial pressure) / blood flow

Question 29

PVR ______ with increasing vascular pressures

Answer 29

Decreases

Question 30

What two mechanisms decreases PVR with increasing vascular pressures

Answer 30

1) Recruitment through opening closed vessels and conducting in previously non-conducting vessels
2) Distension, widening of open vessels

Question 31

For alveolar vessels, what is transmural pressure

Answer 31

Pressure difference between alveolar pressure and vessel lumen pressure

Question 32

For extra-alveolar vessels, what is transmural pressure

Answer 32

Pressure difference between intrapleural pressure and vessel lumen pressure

Question 33

PVR is the lowest when

Answer 33

At FRC

Question 34

At high lung volumes, what happens to the alveolar vessels and extra-alveolar vessels

Answer 34

At high lung volumes, vessel stretching crushes alveolar vessels and pulls open extra-alveolar vessels

Question 35

At low lung volumes, what happens to the alveolar and extra-alveolar vessels

Answer 35

At low lung volumes, extra-alveolar vessels are subject to increased intrapleural pressure. Alveolar vessels are no longer crushed by large alvolai

Question 36

There is increased blood flow at what part of the lungs

Answer 36

Bottom of the lungs

Question 37

In zone 1, what is the line up of PA, Pa, and Pv and what is the blood flow

Answer 37

PA > Pa > Pv, so there is no blood flow

Question 38

In zone 2, what is the line up of PA, Pa, and Pv and what is the blood flow

Answer 38

Pa > PA > Pv, and there is the beginning of blood flow, this is the waterfall effect

Question 39

In zone 3, what is the line up of PA, Pa, and Pv and what is the blood flow

Answer 39

Pa > Pv > PA, and there is the most blood flow in this zone

Question 40

In hypoxic vasoconstriction, what is it determined by?

Answer 40

Determined by PO2 in alveolar gas (PAO2) but not by P arterial O2

Question 41

Oncotic pressure

Answer 41

Movement of H2O due to increase plasma protein concentration

Question 42

If hydrostatic pressure = oncotic pressure, what happens

Answer 42

No net flow in or out of vessel

Question 43

In a healthy individual, hydrostatic _______ oncotic

Answer 43

Hydrostatic exceeds oncotic, so there is a constant flow from lung interstitial fluid to lymph

Question 44

Alveolar lung edema

Answer 44

Fluid in the alveoli themselves, very bad. No gas exchange happening then