Gas exchange

Question 1

Henrys law

Answer 1

The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid

Question 2

Fick’s Law of Diffusion

Answer 2

The rate of gas transfer (V gas) is directly proportional to the tissue area, the diffusion coefficient of the gas, and the difference in the partial pressure of the gas on the two sides of the tissue, and inversely proportional to the thickness of the membrane.

Question 3

PiO2

Answer 3

Partial pressure of inspired O2 ~ 150mmHg

Question 4

PbO2

Answer 4

The partial pressure of oxygen in the atmosphere 760mmHg

Question 5

FiO2

Answer 5

Fraction (percentage) of inspired oxygen from the air at sea level ~ 21% = PiO2

Question 6

PAO2

Answer 6

Partial pressure of oxygen in the surrounding capillaries/the arterial blood ~ 100-105 mmHg

Question 7

Why does the PiO2 change from 160 to 150mmHg by the time it reaches the alveoli?

Answer 7

Due to the air being humidified and moisturized. You must subtract the pressure that the water vapor exerts (PH20) from the PbO2.

Question 8

What is the equation to find the final PiO2?

Answer 8

PbO2 - PH2O {(760mmHg - 47mmHg) x .21}

Question 9

Equation for PAO2

Answer 9

PiO2 - (PaCO2/R) (R=0.8)

Question 10

A-a gradient

Answer 10

The difference in PO2 between the PAO2 and PaO2

Question 11

The formula for A-a gradient

Answer 11

PAO2 - PaO2

Question 12

Normal range of A-a gradient

Answer 12

5 to 10mmHg

Question 13

Factors that affect the A-a gradient

Answer 13

Anatomic shunts, V/Q mismatch

Question 14

Formula for PAO2

Answer 14

(Pb - PH2O) x FiO2 - PaCO2/0.8

Question 15

PaCO2 normal range

Answer 15

35-45 mm Hg

Question 16

PaO2

Answer 16

Partial pressure of oxygen in the surrounding capillaries/the arterial blood ~ 75-100 mmHg

Question 17

What is the V to Q pressure difference in Zone 1 of the lungs?

Answer 17

PA>Pa>Pv

Question 18

What is the V to Q pressure difference in Zone 2 of the lungs?

Answer 18

Pa>PA>Pv

Question 19

What is the V to Q pressure difference in Zone 3 of the lungs?

Answer 19

Pa>Pv>PA

Question 20

What occurs in Zone 1 of the lungs?

Answer 20

In Zone 1 alveolar pressure exceeds that of the pulmonary arterial pressure. Consequently, the pulmonary arteries become compressed, this area is being ventilated but not profused. This is known as dead space and in this zone little to no gas exchange can occur.

Question 21

What occurs in Zone 2 of the lungs?

Answer 21

In Zone 2 Pulmonary arterial pressure exceeds that of Alveolar pressure and Pulmonary venous pressure; however alveolar pressure is still greater than pulmonary venous pressure. The blood flow in this Zone is largely cardiac cycle-dependent.

Question 22

What occurs in Zone 3 of the lungs?

Answer 22

In Zone 3 Pulmonary arterial pressure is greater than Pulmonary venous pressure and both are greater than Alveolar pressure. Typically located in the bottom portion of the lungs, in this Zone pulmonary blood flows past unventilated alveoli and no oxygenation takes place in a condition know as Shunt.

Question 23

What are the four factors that affect diffusion according to Fick?

Answer 23

1. Membrane surface area.
2. The diffusion coefficient of that particular gas for that membrane.
3. The difference in pressure between the gases across the membrane.
4. The thickness of the membrane.