Primary Teaching - Respiratory Physiology

Question 1

Hb oxygen dissociation curve in healthy individual - PaO2 when sats 50%

Answer 1

3.5 kPa

Question 2

Hb oxygen dissociation curve in healthy individual - PaO2 when sats 75%

Answer 2

5.3 kPa

Question 3

Hb oxygen dissociation curve in healthy individual - PaO2 when sats 100%

Answer 3

13.3 kPa

Question 4

Myoglobin dissociation curve

Answer 4

Hyperbolic curve

Question 5

Why is myoglobin dissociation curve steeper than Hb dissociation curve

Answer 5

Myoglobin only binds one oxygen molecule

Question 6

Analogy for environment where Hb has lower affinity for O2

Answer 6

Exercising muscle - eg. heat, higher PaCO2, acidosis, (higher 2,3 DPG + pregnancy don’t fit)

Question 7

Why is there a delay in increasing oxygen carriage post blood transfusion

Answer 7

Stored blood transfusions depletes levels of 2,3 DPG in circulation and therefore causes delay in increase of oxygen carriage post transfusion

Question 8

Haldane effect

Answer 8

Deoxygenated Hb has higher affinity for CO2

Question 9

Bohr effect

Answer 9

Rightward shift of Hb oxygen dissociation curve as PaCO2 / acidosis increases

Question 10

Oxygen requirements of vital organs per minute

Answer 10

200-250 ml/min

Question 11

Modes of transport of O2

Answer 11

Bound to Hb (majority at sea level in healthy)
Dissolved in plasma

Question 12

Oxygen content of blood

Answer 12

CaO2 = (SaO2 x 1.34 x [Hb]) + (PaO2 x 0.023)

(SaO2 x 1.34 x Hb) is oxygen bound to Hb
(PaO2 x 0.023) is oxygen dissolved in plasma
0.023 is oxygen solubility coefficient
1.34 is Hüfner constant, amount of oxygen in millilitres carried by each gram of haemoglobin

Question 13

Oxygen cascade graph

Answer 13

Question 14

Saturated water vapour pressure

Answer 14

6.3 kPa

Question 15

PaO2 in atmospheric air at sea level

Answer 15

21.2 kPa

Question 16

PaO2 in trachea air where humidification occurs

Answer 16

(Atmospheric pressure - saturated water vapour pressure) x PaO2 in atmosphere

(101 - 6.3) x 0.21 = 19.9

Question 17

Alveolar gas equation

Answer 17

PAO2 = FiO2 (PATM – PH2O) – PACO2/RQ

(PATM – PH2O) is (Atmospheric pressure - saturated water vapour pressure) i.e previous step to account for humidification

PACO2 is roughly equal to PaCO2

RQ (Respiratory quotient) = 0.8 in most healthy individuals

Nitrogen is not included in equation as Nitrogen pressure is in equilibrium and does not change and therefore does not alter equation

PAO2 = (0.21 x (101-6.3)) - (5.3/0.8)
= 19.9 - 6.6
= 13.3 kPa

Question 18

Respiratory quotient relevance

Answer 18

0.8
Takes into account CO2 produced and then exchanged
Effected by metabolism so is different in certain food diets e.g pure carbohydrate diets

Question 19

Alveolar - arterial gradient

Answer 19

Less that 2 kPa
Therefore PaO2 is between 11.3 and 13.3 kPa as PAO2 is 13.3 kPa

Question 20

2,3 DPG

Answer 20

2,3 Diphosphoglyceric acid
By product of ATP production / glucose metabolism

Question 21

Methods of CO2 transport in the blood

Answer 21

Conversion to bicarbonate 60%
Carbaminohaemoglobin 30%
Dissolved in plasma 10%

Question 22

CO2 metabolism equation

Answer 22

CO2 + H2O -> H2CO3 -> HCO3- + H+

H2CO3 is carbonic acid, but almost immediately dissociates to Bicarbonate and Proton ion

Catalysed by carbonic anhydrase enzyme

Goes forward in tissues for transport
Goes backwards in pulmonary capillaries for excretion

Question 23

Chloride shift

Answer 23

In venous blood, Hb buffers proton ion produced by bicarbonate production.
Bicarbonate diffuses out of RBC into serum via HCO3-/Cl- exchanger in exchange for chloride ion

Therefore venous blood has higher levels of bicarb and lower levels of chloride

Question 24

Categories of hypoxia

Answer 24

Hypoxaemic hypoxia
Anaemic hypoxia
Histotoxic hypoxia
Circulatory hypoxia

Question 25

Hypoxaemic hypoxia definition

Answer 25

True hypoxia in atmospheric air / Obstructive lung disease

Question 26

Circulatory hypoxia definition

Answer 26

Impaired perfusion of tissues due to reduced circulation / stagnation

Question 27

Circulatory hypoxia examples

Answer 27

Cardiogenic shock / heart failure
Obstructive shock eg tamponade
Distributive shock eg anaphylaxis

Question 28

Histotoxic / cytotoxic hypoxia definition

Answer 28

Cellular dysfunction for oxygen utility

Question 29

Histotoxic / cytotoxic hypoxia examples

Answer 29

CO poisoning
Sepsis
Mitochondrial dysfunction

Question 30

Effect of halothane and sevofluorane on central chemoreceptor response to hypoxaemia

Answer 30

Dampened

Question 31

Cardiovascular effects of hypoxia

Answer 31

Sympathetic response
Increase in cardiac output

Question 32

Effect of hypoxia on cerebral vasculature

Answer 32

As PaO2 drops below 8 kPa, cerebral blood flow exponentially increases with vasodilation

Therefore in neuroprotective measures need to maintain normoxia

Question 33

Approximate spirometry volumes

Answer 33

Total lung capacity 6000 ml
Vital capacity 4500 ml
Tidal volume 500 ml
Inspiratory reserve volume 2500 ml
Functional residual capacity 3000 ml
Expiratory reserve volume 1500 ml
Residual volume 1500 ml

Question 34

Capacity definition

Answer 34

Is the sum of volumes

Eg. FRC = ERV + RV

Question 35

Closing volume definition

Answer 35

Volume of the lungs when small airways begin to close

Differs with age and positioning of patient

Question 36

How to measure closing volume

Answer 36

Fowler’s method

Question 37

Fowler’s method

Answer 37

Single breath nitrogen washout test
Calculates anatomical dead space and closing volume

Question 38

Effect of altitude on barometric pressures of PiO2

Answer 38

Higher altitudes have lower barometric pressures of oxygen

Question 39

Effect of altitude on volatile anaesthetics

Answer 39

Percentage of volatile delivered increased but partial pressure of volatile remains the same and therefore clinical effect remains the same.

Partial pressure of volatile agents determine the depth of anaesthesia, not the percentage