Gaseous diffusion 1

Question 1

What is FO2?

Answer 1

Fractional concentration of oxygen

Question 2

What is PIO2?

Answer 2

Partial pressure of inspired oxygen

Question 3

What is PAO2?

Answer 3

Partial pressure of alveolar oxygen

Question 4

What is PaO2?

Answer 4

Partial pressure of arterial oxygen

Question 5

What is Dalton’s Law?

Answer 5

In a mixture of non-reacting gases, total pressure exerted is sum of individual partial pressures

Question 6

How can you calculate PO2?

Answer 6

FO2 x PB

Question 7

What is Henry’s Law?

Answer 7

C = kP

As the partial pressure of the gas increases, more of the gas dissolves in the liquid

Question 8

Which is more soluble - oxygen or nitrogen?

Answer 8

Oxygen is twice as soluble as nitrogen (higher Henry’s Law constant)

Question 9

Which is more soluble - carbon dioxide or oxygen?

Answer 9

Carbon dioxide is 20x more soluble than oxygen (much higher Henry’s Law constant)

Question 10

What is the bends?

Answer 10

Nitrogen less likely to dissolve in plasma than oxygen
Pressure surrounding you is greater during diving
More nitrogen goes into solution
When you ascend, if you go to quickly, nitrogen will rapidly come out of solution and form bubbles in muscles/SC

Question 11

What 2 factors does the water vapour pressure (PH20) depend on?

Answer 11

Temperature

Saturation

Question 12

What is the water vapour pressure in the lungs?

Answer 12

6.3kPa

Question 13

Is the water vapour pressure in the lungs constant or does it change?

Answer 13

Constant at 6.3kPa

100% saturated

Question 14

What is the alveolar gas equation?

Answer 14

PAO2 = PIO2 - PACO2/R

Question 15

What is the respiratory exchange ratio, R?

Answer 15

CO2 production/O2 consumption

Question 16

What is the PO2 of atmospheric air?

Answer 16

21kPa

Question 17

What is the PO2 in alveolar gas?

Answer 17

13.5kPa

Question 18

What is the PCO2 in alveolar gas?

Answer 18

5.3kPa

Question 19

What is the PH20 in alveolar gas?

Answer 19

6.3kPa

Question 20

What is the PO2 in mixed venous blood?

Answer 20

5.3kPa

Question 21

What drives O2 movement across alveoli into capillary?

Answer 21

Partial pressure gradient

Question 22

What determines the rate of gas transfer?

Answer 22

Partial pressure gradient NOT concentration gradient

Question 23

What limits diffusion of gases in the lung?

Answer 23

Respiratory disease - disrupts the alveolar/capillary unit

Question 24

Which factors affect rate of diffusion across a membrane?

Answer 24

Pressure gradient
Surface area
Thickness

Question 25

What is the equation for rate of transfer of a gas?

Answer 25

DLg (PA - PC) Where DLg = transfer factor PA = alveolar pp PC = capillary pp

Question 26

Why can't we use O2 to measure transfer factor?

Answer 26

Because mean capillary PO2 is unmeasurable

Question 27

What gas is used to measure transfer factor and why?

Answer 27

Carbon monoxide - has a higher affinity for Hb than oxygen (240x higher)

Question 28

What is the equation for gas transfer factor of CO?

Answer 28

``` DLCO = VCO/ PACO VCO = rate of CO uptake PACO = conc of CO in alveolar air ```

Question 29

Which factors reduce the surface area of the lungs?

Answer 29

Emphysema Lung resection Decreased venous return

Question 30

Which factors increase the thickness and reduce gas transfer factor in the lungs?

Answer 30

Fibrosis Collagen vascular diseases Congestive heart failure

Question 31

What 3 factors decrease DLCO?

Answer 31

Reduction in alveolar-capillary area Increased thickness of alveolar-capillary membrane Anaemia

Question 32

Which 2 factors increase DLCO?

Answer 32

Increased pulmonary blood volume (exercise) | Polycythaemia (increased no of RBCs)

Question 33

What is the normal concentration of Hb in the blood?

Answer 33

150g/L

Question 34

What is the oxygen capacity of normal blood?

Answer 34

200ml/L

Question 35

What is the oxygen saturation of pulmonary venous blood?

Answer 35

Nearly 100%

Question 36

What is the oxygen saturation of mixed venous blood returning to the heart?

Answer 36

75%

Question 37

What is the Bohr shift?

Answer 37

Shift of oxygen-Hb dissociation curve to the right due to decrease in pH etc - easier to offload oxygen, e.g. in respiring tissues

Question 38

What happens to the oxygen capacity, content and saturation at high altitudes?

Answer 38

Capacity - normal Content - reduced Saturation - reduced

Question 39

What happens to the oxygen capacity, content and saturation at high altitudes?

Answer 39

Capacity - normal Content - reduced Saturation - reduced

Question 40

What happens to the oxygen capacity, content and saturation in anaemia?

Answer 40

Capacity - reduced Content - reduced Saturation - normal

Question 41

What is the PO2 in mixed expired air?

Answer 41

16kPa

Question 42

What is the PCO2 in mixed expired air?

Answer 42

3.5kPa

Question 43

What is the PH20 in mixed expired air?

Answer 43

Variable