Respiratory expert session - 06.11.17

Question 1

What are the normal PaO2, PaCO2, pH and HCO3- values?

Answer 1

PaO2: 10 - 13.5 kPa
PaCO2: 4.8 - 6 kPa
pH: 7.35 - 7.45
HCO3-: 23 - 27mmol/L

Question 2

What is the alveolar gas equation?

Answer 2

PAO2 = FiO2(Patm - PH2O) - PaCO2/RER

FiO2 - 0.21
Patm - 101kPa
PH2O - 6.25kPa
PaCO2 - from blood analysis 
RER - 0.8

Question 3

What is the alveolar-arterial difference and what is the normal range?

Answer 3

is a measure of the difference between alveolar and arterial oxygen
- 0.5-1.5kPa

Question 4

What type of protein is Hb?

Answer 4

Allosteric protein

Question 5

What is meant by “cooperative binding”?

Answer 5

Binding of oxygen to one haemoglobin subunit causes a conformational change that are relayed to the other subunits, making them more able to bind oxygen by raising their affinity for this molecule - oxygen binding to iron is reversible and changes the structure of the subunit - the new conformation causes the haem groups to become progressively more exposed

Question 6

What is the key purpose of Hb?

Answer 6

increases the total blood oxygen capacity seventy fold in comparison to dissolved oxygen in the blood

Question 7

What form is oxygenated Hb?

Answer 7

has a planar form = referred to as R or relaxed form

Question 8

What does the Bohr effect?

Answer 8

facilitates oxygen release in the tissues

Question 9

What effect does the Bohr effect have on the oxygen-dissociate?

Answer 9

Shifts to the right

because this decreases the pH of the blood which promotes the dissociation of oxygen

Question 10

When does Hb have a higher binding affinity for H+?

Answer 10

Hb has proton binding sites which have a higher affinity for binding H+ in deoxyhaemoglobin than oxyhaemoglobin
- oxygen is pushed off Hb to accommodate proton binding

Question 11

What conc is 2,3-BPG present in the blood?

Answer 11

approx. 5mmol/L

Question 12

Which form of Hb does 2,3-BPG bind to with a greater affinity?

Answer 12

Binds with a greater affinity to deoxygenated Hb (e.g. RBCs near respiring tissue) than it does to oxygenated Hb (e.g. lungs) due to spatial changes
- 2,3-BPG fits in the non-planar de-oxygenated Hb configuration but not in the oxygenated planar formation
-

Question 13

What part of Hb does 2,3-BPG interact with?

Answer 13

interacts with deoxygenated Hb beta subunits decreasing O2 affinity so it allosterically promotes the release of the remaining oxygen molecules bound to Hb

Question 14

What are “salt bridges”?

Answer 14

in the presence of CO2 and H+, charged groups are formed on each subunit - charged groups form salt bridges
These form between 2 subunits and stabilise the deoxygenated form of Hb

Question 15

What light does oxygenated conformation of Hb absorb and reflect?

Answer 15

light in the blue-green range and reflects red light, giving the red appearance of oxygenated blood

Question 16

What light does deoxygenated conformation of Hb absorb and reflect?

Answer 16

Deoxygenated conformation of Hb absorbed light in the orange range and reflects blue light giving a bluish appearance

Question 17

How does CO form?

Answer 17

it is the product of combustion of organic matter under conditions with reduced oxygen supply, preventing the complete oxidation to CO2

Question 18

What forms when CO enters the blood?

Answer 18

Carboxyhaemoglobin - competitive inhibitor for oxygen - affinity is 250 times stronger than its affinity for O2 - therefore it is unlikely to dissociate and once bound it blocks the binding of oxygen to that subunit

Question 19

Why is it relevant that CO is structurally similar to O2?

Answer 19

carboxyhemoglobin therefore favours the planar state raising the oxygen affinity of the remaining unoccupied subunits - this combination significantly reduces the delivery of oxygen to the tissues which is what makes CO so toxic

Question 20

What colour is the blood in CO poisoning ?

Answer 20

it absorbs blue-green light and reflects red giving the Red appearance of oxygenated blood - people look pink

Question 21

What are the symptoms of CO poisoning?

Answer 21

dull headache
weakness
dizziness
nausea or vomiting 
shortness of breath 
confusion 
most of these are due to low oxygenation but nausea is due to gastric paresis

Question 22

What does chronic CO poisoning cause?

Answer 22

Persistent CO creates a state of chronic low oxygen status

• Similar to high altitude
• HR and RR increase
• 4-5 days later RBCs release from bone marrow increases to try and increase oxygen carriage potential

Question 23

When does anaemic hypoxia occur and what happens?

Answer 23

when the oxygen carrying ability of the blood decreases - fewer Hb molecules or oxygen binding sites are available for binding oxygen
All the principles of oxygen diffusion remain the same

Reduction in oxygen delivery to tissue will lead to an increase in capillary perfusion, arteriolar dilation and a reduction in blood viscosity (reduction in Hot)
Increase in RR and HR
- blood flow and oxygen delivery will increase until capacity is met
PaO2 will be unchanged because the Hb are saturated, the lack of O2 delivery is due to too few Hb molecules