Pulmonary Blood Flow, Gas Exchange and Transport Flashcards
What is the supply and function of the bronchial circulation?
- Supplied via the bronchial arteries arising from systemic circulation
- Supplies oxygenated blood to airway smooth muscle , nerves and lung tissue
What makes the pulmonary circulation unique?
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.
What is PAO2?
Alveolar PO2 = 100mmHg, 13.3kPa
What is PACO2?
Alveolar PCO2 = 40mmHg, 5.3kPa
What is PaO2?
Arterial PO2 = 100mmHg, 13.3kPa
What is PaCO2?
Arterial PCO2 = 40mmHg, 5.3kPa
What is PvO2?
Venous PO2 = 40mmHg, 5.3kPa
What is PvCO2?
Venous PCO2 = 46mmHg, 6.2kPa
State the factors that affect gas exchange
- Partial pressure gradient
- Gas solubility
- Available surface area
- Thickness of the membrane
- Various pathologies
The PP in alveoli is the same as the PP in ___?
Systemic arterial blood.
The PP in pulmonary arterial blood (i.e. mixed venous blood) is the same as the PP in ___?
Tissues.
How does emphysema affect gas exchange?
PAO2 = normal/low PaO2 = low
How does fibrotic lung disease affect gas exchange?
PAO2 = normal/low PaO2 = low
How does pulmonary oedema affect gas exchange?
PAO2 = normal PaO2 = low
How does asthma affect gas exchange?
PAO2 = low PaO2 = low
Define ventilation
Air getting into alveoli (L/min).
Define perfusion
Local blood flow (L/min).
Explain the relationship between ventilation and perfusion and its significance in health
Ventilation in alveoli is matched to perfusion through pulmonary capillaries.
Define shunt
The passage of blood through areas that are poorly ventilated (perfusion>ventilation). The opposite of alveolar dead space.
Define alveolar dead space
The alveoli that are ventilated but not perfused.
Define physiologic dead space
Alveolar dead space + anatomical dead space
Identify the forms in which CO2 is carried in the blood
- 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.)
State the differences between partial pressure and gas content
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.
Describe the role of haemoglobin in the transport of O2 in the blood
200ml/L of O2 is carried by haemoglobin in RBCs (approx. 98%), compared to only the 3ml/L dissolved in solution.
What effect do foetal haemoglobin and myoglobin have on the oxyhemoglobin dissociation curve?
They shift it to the left i.e. they become saturated at a lower PO2.
Describe the factors that affect the oxyhaemoglobin dissociation curve
- 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%
Describe CO poisoning
- 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
How does hypoventilation affect ECF pH?
- Causes CO2 retention
- Increases H+ ions (from carbonic acid in RBCs)
- Causes respiratory acidosis
How does hyperventilation affect ECF pH?
- Causes more CO2 to leave the body
- Decreases H+ ions
- Causes respiratory alkalosis
