Gas Diffusion, Transport, and Exchange

Question 1

Central Gas Law

Answer 1

PV=nRT

Pressure (mmHg) Volume (L) = Moles x gas constant x temp

Question 2

What constants are used for gas phase calculations?

Answer 2

BTPS

Body temp (37C or 310K), Ambient pressure, saturated with water vapor (47mmHg).

Question 3

What constants are used for gas dissolved in blood?

Answer 3

STPD

Standard Temp (0C or 273K), Standard Pressure (760mmHg), Dry gas

Question 4

How do pressure and volume of a gas relate?

Answer 4

P1V1=P2V2. During inspiration, there’s increased lung volume, which causes gas pressure to decrease.

Question 5

How to calculate partial pressure of a dry gas?

Answer 5

Px = Pb x F

Where Pb is barometric pressure and F is fractional concentration

Question 6

How to calculate partial pressure of humified gas?

Answer 6

Px = (Pb-PH2O) x F

PH2O at 37C is 47 mmHg

Question 7

True or false?

The sum of partial pressures of all gases in a mixture is the total pressure of the mixture.

Answer 7

True!

Question 8

What percent of atmospheric air at 760mmHg is Oxygen?

Answer 8

21%

Question 9

How does high altitude affect PO2 of inspired air?

Answer 9

Decreases PO2 of inspired air due to low barometric pressure.

Question 10

Concentration of a free dissolved gas equation?

Answer 10

Cx = Px x S. This applies to a dissolved gas that is free in solution.

Question 11

True or false?

Only a dissolved gas, not a bound gas or chemically modified gas, contributes to its partial pressure.

Answer 11

True

Question 12

Fick’s Law of Simple Diffusion. Calculate rate of transfer.

Answer 12

Vx = (DAP)/ X

Diffusion coefficient, surface area, pressure gradient, divided by thickness.

Question 13

What factors affect diffusion coefficient?

Answer 13

Molecular weight and solubility

Question 14

Difference in diffusion between O2 and CO2

Answer 14

CO2 has a 20X higher D.

Question 15

How is N2 carried in blood?

Answer 15

Exclusively in dissolved form.

Question 16

How is O2 carried in the blood?

Answer 16

Mostly (98%) bound to hemoglobin. CO can also bind to hemoglobin.

Question 17

How is CO2 carried in the blood?

Answer 17

Chemically modified to HCO3-.

Question 18

Diffusion limited gas exchange

Answer 18

Amount of gas that is transported from alveoli to capillaries is limited by diffusion. This is true for CO, and transport of O2 in emphysema, fibrosis, and exercise.

Question 19

Perfusion limited gas exchange

Answer 19

The amount of gas transported is based on the blood flow. This is true for O2, CO2. Occurs in the first 1/3 of capillary.

Question 20

Oxygen binding capacity

Answer 20

1 gram of Hba can bind 1.34 ml O2 when 100% saturated.

Question 21

Concentration of Hb in blood? How much O2 can it hold?

Answer 21

15 g/dL. Can hold 20.1 mL O2.

Question 22

How to calculate O2 bound to Hb

Answer 22

Binding Capacity X % Saturation

Question 23

O2 delivery equation

Answer 23

O2 Delivery = Cardiac Output x (Oxygenated Hb + Dissolved O2)

Question 24

What causes rightward shifts in the Hb-O2 curve.

Answer 24

Increases in temp, Co2, [H], 2,3 DPG. Causes faster unloading into tissues.

Question 25

Why is Co dangerous?

Answer 25

Because its affinity for Hb is 250x that of O2.

Question 26

Conversion of CO2L

Answer 26

Dissolved CO2 in bloodstream. 93% is taken up into RBC’s, 90% is converted to H2CO3 by carbonic anhydrase. H2CO3 dissociates into H+ and HCO3. H+ buffered, HCO3 pushed into plasma via exchange with Cl.

Question 27

Anion Exchange Protein (3 Band)

Answer 27

Changes HCO3- with Cl- on RBCs.

Question 28

A-a gradient.

Answer 28

The difference in PO2 of alveolar gas and arterial blood. Normally less than 12 mmHg.

Question 29

Calculate A-a gradient

Answer 29

A-a = (PiO2 - PACO2/R) - PaO2

Question 30

Why does A-a gradient change?

Answer 30

If there are shunts or diffusion defects. Anatomic probles.