Pulmonary blood flow, gas exchange and transport

Question 1

How does alveolar ventilation and compliance change from the apex to the base of the lung?

Answer 1

Increased alveoli ventilation and compliance in the base of the lungs

Question 2

What circulation is responsible for supplying nutrition to the lungs?

Answer 2

Bronchial circulation - feeds airways smooth muscle, nerves and lung tissue

Question 3

Difference between PA and Pa

Answer 3

PA = pressure in alveolar air
Pa = pressure in arterial blood

Question 4

What are the tissue values of P02 and PCO2

Answer 4

PO2 = 40mmHg
PCO2 = 46mmHg

Question 5

What are the lung values for PO2 and PCO2?

Answer 5

PO2 = 100mmHg
PCO2 = 40mmHg

Question 6

What affects the rate of diffusion across a membrane?

Answer 6

Directly proportional to:
 - partial pressure gradient
 - gas solubility
 - available surface area
Inversely proportional to:
 - thickness of membrane

Question 7

How does emphysema affect gas exchange?

Answer 7

Fewer and larger alveoli through destruction, leading to a reduction of surface area for gas exchange

Question 8

How does fibrosis affect gas exchange?

Answer 8

Fibrotic tissue around elastic fibres separates the capillaries from the type I pneumocytes while also restricting lung expansion, affecting the uptake of O2 from air (inhalation)

Question 9

What does mismatch of ventilation and perfusion lead to ?

Answer 9

Type 1 respiratory failure

Question 10

Why is blood flow to the base of the lungs high?

Answer 10

Arterial pressure exceeds alveolar pressure, making vascular resistance low.

Question 11

Why is blood flow to the apex of the lungs low?

Answer 11

Arterial pressure is lower than alveolar pressure, causing increased vascular resistance which impedes flow

Question 12

Describe a pulmonary shunt and how the body responds to it

Answer 12

Ventilation < perfusion

Shunt is when the alveoli are perfused as normal but ventilation fails to supply there perfused region. This leads to the induction of vasoconstriction of these blood vessels to the poorly ventilated regions of the lung

Question 13

Describe alveolar dead space and how the body responds to it

Answer 13

Ventilation > perfusion

When ventilation is taking place but perfusion isn’t, leading to the body inducing pulmonary vasodilation and bronchial constriction

Question 14

Whats the difference between alveolar and anatomical dead space?

Answer 14

Alveolar - alveoli that are ventilated but not perfused

Anatomical - air in the conducting zone of the lungs not available for gas exchange

Question 15

What is physiological dead space?

Answer 15

Alveolar dead space + anatomical dead space

Question 16

Define pulmonary pressure

Answer 16

Systolic - 25mmHg
Diastolic - 8mmHg

Why its so affected by gravity

Question 17

Why does CO2 diffuse more rapidly?

Answer 17

Greater solubility

Question 18

How much O2 dissolves into the blood (without Hb)?

Answer 18

3ml/L

Question 19

How much does Hb increase the O2 carrying capacity of blood?

Answer 19

3ml/L to 200ml/L

Question 20

How do you calculate O2 delivery to the lungs?

Answer 20

Arterial content of O2 x cardiac output

Question 21

What % of arterial O2 is extracted by peripheral tissues at rest?

Answer 21

25% (02 demand = 250ml/min, supply is 1000ml/min)

Question 22

What % of O2 in the blood is bound to Hb?

Answer 22

98%

Question 23

How much O2 does Hb bind?

Answer 23

4 molecules of O2 = 1.34ml 02/g of Hb

Question 24

What % of total Hb is HbA?

Answer 24

92%

Question 25

How saturated is Hb at normal systemic arterial pressure (PO2 of 100mmHg)?

Answer 25

~100%

Question 26

How saturated is Hb at normal systemic venous pressure (PO2 of 40mmHg)?

Answer 26

75%

Question 27

Which has a higher affinity for O2 - myoglobin or foetal myoglobin?

Answer 27

Myoglobin

Question 28

Define anaemia

Answer 28

Any condition where the O2 carrying capacity of blood is compromised e.g. iron deficiency, B12 deficiency, haemorrhage etc PaO2 is normal but total blood O2 is low

Question 29

What factors decrease the affinity of Hb for O2?

Answer 29

Decreased pH (acidic) Increased PCO2 Increased temperature Binding of 2,3 - diphosphoglycerate

Question 30

What factors increase the affinity of Hb for O2?

Answer 30

Increased pH (alkalosis) Decreased PCO2 Decreased temperature

Question 31

What is 2,3-diphosphoglycerate?

Answer 31

Synthesised by RBCs, and is increased in situations associated with inadequate O2 supply e.g. heart/lung disease, living at high altitude. Aims to help maintain O2 release

Question 32

Where does carbon monoxide come from?

Answer 32

Incomplete combustion of carbon fuel e.g. car exhaust fumes, faulty heating appliances, lawn mowers

Question 33

How does the Hb binding affinity of CO compare to that of O2?

Answer 33

Affinity 250x greater than O2

Question 34

What PCO is required for damage?

Answer 34

0.4mmHg

Question 35

What are the symptoms of carbon monoxide poisoning?

Answer 35

``` Hypoxia Anaemia Nausea Headaches Cherry red skin Can lead to brain damage and death ```

Question 36

How does carbon monoxide poisoning affect RR?

Answer 36

Unaffected due to normal PCO2

Question 37

How do you treat carbon monoxide poisoning?

Answer 37

Removal from source | 100% O2 till PaO2 increases

Question 38

What are the 5 types of hypoxia?

Answer 38

``` Hypoxic hypoxia Anaemic hypoxia Ischaemic/stagnant hypoxia Histotoxic hypoxia Metabolic hypoxia ```

Question 39

How is CO2 transported in the blood?

Answer 39

70% - forms carbonic acid in RBCs, which is then broken by carbonic anhydrase into bicarbonate and H+ ions 23% - binds deoxyhaemoglobin 7% - dissolved in plasma

Question 40

What is formed when CO2 binds to deoxyhaemoglobin in RBCs?

Answer 40

Carbamino compounds

Question 41

What is the main function of carbonic anhydrase?

Answer 41

Interconverts CO2 as carbonic anhydrase and bicarbonate to maintain acid-base balance in the blood

Question 42

What does hypoventilation lead to clinically?

Answer 42

Respiratory acidosis by CO2 retention

Question 43

What does hyperventilation lead to clinically?

Answer 43

Respiratory alkalosis

Question 44

What are the possible uses of respiratory acidosis and alkalosis in the body as a beneficial phenomenon?

Answer 44

Can be used to counteract metabolic acidosis/alkalosis to help return acid-base balance to normal