Resp. 3 - Diffusion and V-Q Relations

Question 1

Dyuring diffusion, what goes into ther alveoli and out of them?

Answer 1

CO2 coming out of blood, into alveoli 9expired through lungs) and O2 diffuses form alveoli into blood.

Question 2

• CO2 is 20X more soluble then O2. Therfore

Answer 2

diffusion constant for CO2 is greater then O2.

If we have a solution in which Po2 and PCO2 are the same, the conc. Of CO2 would be a lot higher.

Question 3

Ficks law

Answer 3

How gas gets through BBB. Diffuses through respiratory membrane (thin).

Vgas=A/T D(P1-P2)

• VGAS direct with A, D, and diff in P

Question 4

Diffusion constant is

Answer 4

Solubility / M.W

Question 5

Partial pressure in atmosphere

Answer 5

Nitrogen 78.5%
Oxygen 20.93%
H2O 0.5%
Carbon Dioxide 0.04%

Question 6

Partial pressure in alveoli

Answer 6

Nitrogen 74.9%
Oxygen 13.7%
H2O 5.2%
Carbon Dioxide 6.2%

Question 7

• The percentages of gases change as we go into the lungs, because the lungs have

Answer 7

metabolic processes, and so CO2 goes form negligible to significant, as as out bodies are warm, H2O increases a lot too. So N2 and O2 decrease.

Question 8

Because of normal shunts, the amount of O2 in

Answer 8

arterial blood is always < theoretical maximum because of the little bit of CO2 that goes back to the left side of the heart

Question 9

PO2 and PCO2 (mmHg)

Atmosphere

Answer 9

PO2: 160
PCO2: 0.3

Question 10

PO2 and PCO2 (mmHg)

Alveolar air

Answer 10

PO2: 100
PCO2: 40

Question 11

PO2 and PCO2 (mmHg)

Pulmonary veins

Answer 11

PO2: 100
PCO2:40

Question 12

PO2 and PCO2 (mmHg)

Systemic arteries

Answer 12

PO2: 100
PCO2: 40

Question 13

PO2 and PCO2 (mmHg)

Cells

Answer 13

PO2: <40
PCO2: >46

Question 14

PO2 and PCO2 (mmHg)

Systemic veins

Answer 14

PO2: 40
PCO2: 46

Question 15

PO2 and PCO2 (mmHg)

Pulmonary arteries

Answer 15

PO2: 40
PCO2: 46

Question 16

What are the pressure gradients found for O2 and CO2

Answer 16

Two gradients,

1) between systemic capillaries & cells
2) alveoli and pulmonary capillaries

CO2 is 6mmHg
O2 is 60mmHg

Question 17

• The reason why O2 require 60mmHg to get it into the cells and CO2 only require 6mmHg to get it into the blood is because of

Answer 17

Fiks law, the diffusion constant term, and the solubility of CO2 is 20X more then O2

Question 18

An increase in altitude leads to a

Answer 18

Decrease in:

• atmospheric pressure
• PO2 in air
• PO2 in alveoli
• PO2 in arterial blood

Question 19

Limitation:

Answer 19

This means that equilibration does not occur between the PO2 in the pulmonary capillary blood and alveolar gas.

Question 20

Kind of limitations

Answer 20

Perfusion and diffusion limitation

Question 21

Something that causes a perfusion limitation (example)

Answer 21

if there’s a reduction in blood flow to the lungs causing the partial pressure of O2 leaving the lungs to be less then the partial pressure going into the aveoli, its perfusion.

Question 22

At rest,

an increase in diffusion would cause ?
A decrease in diffusion would cause?

Answer 22

No limitation

No limitation

Question 23

During exercise,

An increase in blood flow would cause?

A decrease in diffusion AND increase in blood flow would cause?

Answer 23

• no limitation

- DIFFUSION LIMITATION

Question 24

At high altitude,

A decrease in diffusion would cause ?

Answer 24

A diffusion limitation.

Question 25

What is the concentration gradient for CO2 going into the alveoli.

Answer 25

6 mmHg

Between PvCO2 (46) and PaCO2 (40)

Question 26

During the diffusion of CO2,

A decrease in diffusion would cause?
An increase in blood flow would cause?
A decrease in diffusion AND an increase in blood flow causes?

Answer 26

No limitation
No limitation
LIMITATION

Question 27

Regional differences in ventilation due to gravity and posture:

Answer 27

• ventilation not equal throughout the lungs, due to gravity and posture.
• Lying down, highest ventilation is at the back of the lungs.

Question 28

Regional differences in Plp:

Answer 28

• Plp is more (-) at top of lungs.
• Plp pressure generated by the balance between elastic recoil of the lung and the elastic chest wall.
• Weight of lungs is affected by gravity
At the start of inspiration, aveoli at bottom of lung are more deflated

Question 29

At the start of inspiration, aveoli at bottom of lung are more deflated cuz of

Answer 29

Ptp that generated lung V is influenced by Plp. During inflation aveoli in bottom of lung do the best since lil changes in Plp = large changes in lung V.

Question 30

Where is airflow / ventilation the greatest in the lungs ?

Answer 30

At the bottom due to gravity

Question 31

What is the ventilation perfusion ratio

Answer 31

Ventilation(airflow) / blood flow (V/Q)

Ratio between ventilation (O2 into alveoli & CO2 out) and perfusion (O2 out of alveoli and CO2 in).

Question 32

The ventilation perfusion ratio

• More ventilation =
• More perfusion =

Answer 32

• More ventilation = PO2 and PCO2 in alveoli similar to atmosphere P.
• More perfusion = PO2 and PCO2 in alveoli similar to mixed venous blood.

Question 33

Why is the ventilation perfusion ratio increase exponentially?

Answer 33

• this is cuz blood flow decreases at a greater rate, so the denominator decreases faster then airflow. Resulting in VQ ratio that exponentially increases.

Question 34

why is the VQ ratio less then 1 at the beginning?

Answer 34

• This is cuz you have more blood flow (more gravity dependant) at the bottom of the lung then you would airflow (denominator is greater then numerator)

Question 35

DEADSPACE unit

Answer 35

• Lots of ventilation, but no perfusion (possibly due to blood clot)
• PO2 in alveoli will INC in the alveoli and PCO2 will DEC since there’s no gas exchange b/w alveoli and capillaries.
• Doesn’t contribute to gas exchange.

Question 36

Shunt Unit

Answer 36

• Caused by airway obstruction = collapsed bronchi and bronchioles
• No gas exchange
• Blood that passes through this system is determined by a shunt (doesn’t get oxygenated)

Question 37

Silent unit

Answer 37

• no blood flow or ventilation
• hypoxic vasoconstriction occurs in blood vessel heading to the aveoli whose airflow has been reduced, this is in response to reduced airflow to aveoli. This then moved more blood towards aerated units, so its a GOOD THING!

Question 38

Ventilation-Perfusion Inequality

- this means that ventilation and blood flow are

Answer 38

mismatched in various regions of the lung with the result that all gas transfer becomes inefficient.

Question 39

Is the ventilation and perfusion unit form throughout the lungs?

Answer 39

No

- Ventilation and perfusion are both greater at the bottom of the lungs (perfusion more so)

Question 40

• compared to the top of the lung

Answer 40

decrease from the bottom of the lungs to the top of the lungs