Physical Principles of Gas Exchange

Question 1

What is Net Diffusion of a Gas

Answer 1

Movement of a gas in one direction is the effect of a concentration gradient

Question 2

What is the composition of AIR

Answer 2

Air is mainly 79% nitrogen and 21% oxygen

Question 3

Nitrogen Partial Pressure in Atmosphere

Answer 3

79% of 760mmHg (1 atmosphere)=600mmHg

Question 4

What is Henry’s Law

Answer 4

Solubility of a gas in a liquid depends on temperature, the partial pressure of the gas over the liquid, the nature of the solvent and the nature of the gas

Question 5

What isSolubility Coefficient

Answer 5

The measurement of molecules being either attracted to or repelled by water.

Question 6

What does it mean when something is Highly Soluble

Answer 6

When dissolved molecules are attracted by water, more can be accumulated without building up excess pressure in solution

Question 7

Poorly Soluble

Answer 7

Molecules that are repelled by water will dissolve less and have a lower concentration

Question 8

Carbon Dioxide solubility

Answer 8

Carbon Dioxide is 20 times more soluble than Oxygen

Question 9

Net Diffusion

Answer 9

Net diffusion is determined by the difference of partial pressures between gas in alveoli and the blood.

Question 10

What happens if pp of gas in alveoli > blood?

Answer 10

Then the gas moves into the blood

Question 11

What happens of pp of gas in blood>alveoli?

Answer 11

Then the gas moves into the alveoli.

Question 12

6 Factors which affect gas diffusion rates.

Answer 12

1. Pressure Differences.
2. Gas solubility in fluid.
3. Area of fluid.
4. Distance which gas must diffuse.
5. Molecular weight of gas.
6. Temp of fluid (constant in body).

Question 13

Renewal of Alveolar Air

Answer 13

Each breath replaces approx a seventh of FRC.
FRC roughly 2500ml.
This prevents sudden changes in gas concentration

Question 14

Normal Alveolar PO2 is?

Answer 14

100 mmHg

Question 15

Normal Alveolar PCO2 is?

Answer 15

40 mmHg

Question 16

4 Factors that affect rate of gas diffusion through the respiratory membrane.

Answer 16

1. Thickness of respiratory membrane.(i.e. edema/fibrosis increase thickness and decrease gas diffusion)
2. Surface area of respiratory membrane(i.e. emphysema coalesces alveoli into larger chambers, decreases surface area, decreases rat of diffusion).
3. Diffusion Coefficient(ie. solubility and molecular weight of gas–CO2 diffuses 20x faster than O2).
4. Pressure differences accross resp membrane (ie. diff in pp between alveoli and blood),

Question 17

In Normal deoxygenated blood the PO2 and PCO2 is?

Answer 17

PO2=40

PCO2=45

Question 18

V/Q= Zero when?

Answer 18

When there is blood flow, but no alveolar ventilation (complete airway obstruction).

Question 19

V/Q=Infinity when?

Answer 19

When there is alveolar ventilation, but no blood flow (Pulmonary Artery Obstruction).

Question 20

Inspired air PO2 and PCO2?

Answer 20

PO2=150

PCO2=0

Question 21

Normal Alveolar PO2 and PCO2 pp?

Answer 21

PO2=100

PCO2=40

Question 22

Physiologic Shunt

Answer 22

Shunt=perfusion but no ventilation.

V/Q is below normal.

Question 23

Physiologic Dead Space

Answer 23

Dead space=ventilation but no perfusion.

V/Q greater than normal.

Question 24

What is the diffusion coefficient?

Answer 24

Characteristics of a gas which affect the ability and rate of net diffusion

Question 25

Which two characteristics of a gas affect the ability and rate of net diffusion?

Answer 25

1. Solubility of a gas molecule.

2. Molecular weight.