Pulmonary Blood Flow, Gas Exchange and Transport

Question 1

What is the supply and function of the bronchial circulation?

Answer 1

• Supplied via the bronchial arteries arising from systemic circulation
• Supplies oxygenated blood to airway smooth muscle , nerves and lung tissue

Question 2

What makes the pulmonary circulation unique?

Answer 2

It is a high flow, low pressure system (systolic = 25mmHg, diastolic = 8mmHg, systemic = 120mmHg). Low pressure allows gravity to have more of an effect, which explains the variability of blood flow in the lungs.

Question 3

What is PAO2?

Answer 3

Alveolar PO2 = 100mmHg, 13.3kPa

Question 4

What is PACO2?

Answer 4

Alveolar PCO2 = 40mmHg, 5.3kPa

Question 5

What is PaO2?

Answer 5

Arterial PO2 = 100mmHg, 13.3kPa

Question 6

What is PaCO2?

Answer 6

Arterial PCO2 = 40mmHg, 5.3kPa

Question 7

What is PvO2?

Answer 7

Venous PO2 = 40mmHg, 5.3kPa

Question 8

What is PvCO2?

Answer 8

Venous PCO2 = 46mmHg, 6.2kPa

Question 9

State the factors that affect gas exchange

Answer 9

• Partial pressure gradient
• Gas solubility
• Available surface area
• Thickness of the membrane
• Various pathologies

Question 10

The PP in alveoli is the same as the PP in ___?

Answer 10

Systemic arterial blood.

Question 11

The PP in pulmonary arterial blood (i.e. mixed venous blood) is the same as the PP in ___?

Answer 11

Tissues.

Question 12

How does emphysema affect gas exchange?

Answer 12

PAO2 = normal/low 
PaO2 = low

Question 13

How does fibrotic lung disease affect gas exchange?

Answer 13

PAO2 = normal/low 
PaO2 = low

Question 14

How does pulmonary oedema affect gas exchange?

Answer 14

PAO2 = normal 
PaO2 = low

Question 15

How does asthma affect gas exchange?

Answer 15

PAO2 = low
PaO2 = low

Question 16

Define ventilation

Answer 16

Air getting into alveoli (L/min).

Question 17

Define perfusion

Answer 17

Local blood flow (L/min).

Question 18

Explain the relationship between ventilation and perfusion and its significance in health

Answer 18

Ventilation in alveoli is matched to perfusion through pulmonary capillaries.

Question 19

Define shunt

Answer 19

The passage of blood through areas that are poorly ventilated (perfusion>ventilation). The opposite of alveolar dead space.

Question 20

Define alveolar dead space

Answer 20

The alveoli that are ventilated but not perfused.

Question 21

Define physiologic dead space

Answer 21

Alveolar dead space + anatomical dead space

Question 22

Identify the forms in which CO2 is carried in the blood

Answer 22

• 7% dissolved in plasma and RBCs
• 23% combine in RBCs with deoxyhaemoglobin to form carbamino compounds
• 70% combine in RBCs with water to form carbonic acid (dissociates to form bicarbonates and H+ ions)
  (Bicarbonates move out of RBCs in exchange for Cl- and H+ ions attach to haemoglobin. Reverse happens in pulmonary capillaries, leading to CO2 moving into lungs.)

Question 23

State the differences between partial pressure and gas content

Answer 23

Partial pressure;
- Refers purely to O2 in solution
- Determined by O2 solubility and PO2 in the gaseous phase that drives O2 into solution
- PO2 in solution = PO2 in the gaseous phase that result in the O2 concentration in the liquid phase
This is not the same as gas content/conc. as that varied depending on what phase the gas is in.

Question 24

Describe the role of haemoglobin in the transport of O2 in the blood

Answer 24

200ml/L of O2 is carried by haemoglobin in RBCs (approx. 98%), compared to only the 3ml/L dissolved in solution.

Question 25

What effect do foetal haemoglobin and myoglobin have on the oxyhemoglobin dissociation curve?

Answer 25

They shift it to the left i.e. they become saturated at a lower PO2.

Question 26

Describe the factors that affect the oxyhaemoglobin dissociation curve

Answer 26

• High pH (alkalosis) shifts the curve to the left
• Low PCO2 shifts the curve to the left
• Low temperature shifts the curve to the left
• No DPG shifts the curve to the left, however saturation cannot go higher than 90%

Question 27

Describe CO poisoning

Answer 27

• Carboxyhaemoglobin has an affinity 250x greater than O2
• Symptoms: hypoxia, anaemia, nausea, headaches, cherry red skin and mucous membranes, brain damage, death
• RR unaffected due to normal PCO2

Question 28

How does hypoventilation affect ECF pH?

Answer 28

• Causes CO2 retention
• Increases H+ ions (from carbonic acid in RBCs)
• Causes respiratory acidosis

Question 29

How does hyperventilation affect ECF pH?

Answer 29

• Causes more CO2 to leave the body
• Decreases H+ ions
• Causes respiratory alkalosis