Gaseous Diffusion And Transport

Question 1

Definition of fractional concentration (FO2/%)

Answer 1

The proportion of air that is made up of O2

Question 2

Definition of partial pressure (PO2)

Answer 2

The pressure at which a gas in the air exerts

Question 3

Definition of barometric pressure (Pb)

Answer 3

Total pressure of gases in the atmosphere

Question 4

Definition of inspired PiO2, FiO2

Answer 4

Partial pressure of O2/fractional concentration of O2 in moistened inspired air at the end of the trachea

Question 5

Definition of alveolar PAO2,FAO2

Answer 5

Partial pressure of O2/fractional concentration of O2 in the alveoli

Question 6

Definition of arterial PaO2/FAO2

Answer 6

Partial pressure of O2/fractional concentration of O2 in the arterial blood

Question 7

Definition of dead space

Answer 7

Airway volume with no gas exchange

Question 8

Definition of anatomic dead space (ADv)

Answer 8

All except alveoli and respiratory bronchioles

Question 9

Definition of physiologic dead space (PDv)

Answer 9

Anatomic dead space and areas where gas exchange is dysfunctional

Question 10

Definition of saturation

Answer 10

Depends on how much air has been in contact with the water

Question 11

Definition of polycythaemia

Answer 11

Increase in no of RBCs in the blood

Question 12

Definition of capacity

Answer 12

How much something is capable of carrying

Question 13

What is Dalton’s Law

Answer 13

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

Question 14

What is Pb at sea level
What is FO2
What is PO2 as a result

Answer 14

Pb = 101kPa
FO2 - 0.209
PO2 = 101 x 0.209 =21kPa

Question 15

How does Pb, FO2, PO2 change at altitude?

Answer 15

Pb falls
FO2 doesn’t change
PO2 falls

Question 16

What is Henry’s Law
What happens when the partial pressure increases
How would you increase partial pressure

Answer 16

C = kp

C = conc of dissolved gas at equilibrium
k = solubility
p = partial pressure

Partial pressure increases = more dissolves
Change PP by changing volume

Question 17

Describe the relative solubilities of N2, O2 and CO2

What is the bends?

Answer 17

O2 = 2x more soluble than N2
CO2 = 20x more soluble than O2

If Pb decreases too rapidly (rise to the surface too fast), N2 isn’t breathed out and gas accumulates in blood and joints
Causes severe pain

Question 18

What factors affect PH2O
What is the value of PH2O
How does PH2O affect PAO2

Answer 18

Affected by temp and saturation, NOT BY PB

6.3kPa

As you breathe in, air comes into contact with moisture in lungs = 100% saturation

Question 19

In atmospheric air, what is
PO2
PCO2
PH2O

Answer 19

PO2
-21

PCO2
-0

PH2O
-var

Question 20

In expired air, what is
PO2
PCO2
PH2O

Answer 20

PO2
-16

PCO2
-3.5

PH2O
-var

Question 21

In inspired tracheal air, what is
PO2
PCO2
PH2O

How would you calculate these values

Answer 21

PO2
-20

PCO2
-0

PH2O
-6.3

(Pb-PH2O) x FiO2
(101-6.3) x 0.209 =20 ish

Question 22

In alveolar air, what is
PO2
PCO2
PH2O

How would you calculate these values

Answer 22

PO2
-13.5

PCO2
-5.3

PH2O
-6.3

PO2 = PiO2 - PACO2/R
13.5 = 20 - 5.3/0.8

Question 23

How do you calculate PAO2 as you cannot measure it directly and why

What is the normal value for R

Answer 23

Can’t be measured directly as O2 input and CO2 output are not equal

PAO2 = PiO2 - PACO2/R

R=CO2 production/O2 consumption
R=0.8

Question 24

Describe gas exchange of O2 and CO2 in the pulmonary arteries and veins

What are the PP values in the pulmonary arteries, alveoli, pulmonary vein

What can happen when flow is abnormal/too fast

Answer 24

O2 movement powered by PP grad

Pulmonary arteries PO2 = 5.3
Alveoli = 13.5
Pulmonary veins PO2 = 13.5

CO2 diffuses slower than O2 due to increased MW
Solubility is higher equilibrates rapidly

Pulmonary arteries PCO2 = 6.1
Alveoli = 5.3
Pulmonary veins = 5.3

Less time for gas diffusion => hypoxia/hypercapnia

Question 25

Name the 3 capillary layers

Answer 25

Alveolar epithelium Interstitial fluid Endothelium

Question 26

How would you measure the rate of gas diffusion across the capillary wall

Answer 26

``` Rate = c∆ x A/x∆ x sol/√MX Rate = Dlg (PA -Pc) ``` CO has a v high affinity for haem, none dissolved in blood Patient inhales CO tracer gas, composition of exhaled gas examined -If DlCO = 100% => efficient gas transfer

Question 27

How do these factors affect the DlCO - Surface area of barrier - Thickness of barrier - Anaemia - Polycythaemia - Increasd pulmonary BV in exercise

Answer 27

SA - reduced in emphesyma, lung resection, reduced venous return - Decreased DlCO Thickness - increased in fibrosis, congestive heart failure, vascular diseases - decreased DlCO Anaemia - decreased Hb to pick up O2 - decreased DlCO Polycythaemia - increased Hb to pick up O2 - increased DlCO Increased pulmonary BV in exercise - Increased effective area - increased DLCO

Question 28

Describe how gas exchange occurs between the capillaries and tissues What problems could occur at the venous end of the capillaries

Answer 28

O2 diffuses down the partial pressure gradient Arterial end = 13.5 Venous end = 5.3 Venous end less likely to receive highly oxygenated blood, if PO2 too low => diffusion slows down => hypoxic tissue

Question 29

Describe how O2 is loaded and unloaded from RBCs What is the PO2, O2 content, SaO2 in venous blood and arterial blood What is the Bohr effect?

Answer 29

Sigmoid relationship between O2 sats and PP Venous blood - PO2 = 5.3 - O2 content = 150ml/l - SaO2 = 75% Arterial - PO2 = 13.5 - O2 content = 200ml/l - SaO2 = 100% Bohr effect - decreased pH - increased pCO2 - increased temp - increased 2, 3 DPG => MORE O2 OFFLOADED

Question 30

What PO2 is good in venous blood? | At what values should we be concerned and why?

Answer 30

PO2 in venous blood > 8 => good oxygenation of tissues PO2 < 8 => O2 offloads too quickly (on steepest part of curve), tissue on venous side => hypoxic

Question 31

Describe how altitude affects - O2 capacity - Pb - PiO2 - PaO2 - SaO2

Answer 31

O2 capacity -normal Pb -decreased PiO2 -decreased PaO2 -decreased SaO2 -decreased

Question 32

Describe how anaemia affects - O2 capacity - Pb - PiO2 - PaO2 - SaO2

Answer 32

O2 capacity -decreased due to less Hb Pb -normal PiO2 -normal PaO2 -normal SaO2 - normal

Question 33

What is the difference between capacity, content and saturation?

Answer 33

Capacity -how much O2 a RBC can carry Content -How much O2 a RBC is carrying Saturation -Percentage of Hb carrying O2