Blood supply, gas exchange, ventilation & perfusion Flashcards
What does the bronchial circulation supply?
Supplies oxygenated blood via bronchial arteries from the systemic circulation to airway smooth muscle, nerves and lung tissue.
Where do the Left and right pulmonary arteries arise from?
The right ventricle
What does the Left and Right pulmonary artery carry?
Entire cardiac output from RV
What does the pulmonary artery supply?
The dense capillary network surrounding the alveoli
Where does the blood travel after the capillary network surrounding the alveoli?
Travels to the left atrium via the pulmonary vein
How is the pulmonary circulation described?
High flow low pressure system.
What is the partial pressure of Oxygen in the alveoli?
100mmHg
What is the partial pressure of CO2 in the alveoli?
40 mmHg
How does the air diffuse across the membranes between the alveoli and the blood circulation?
Diffusion across the partial pressure gradient
What does A stand for?
Alveolar
What does a stand for?
Arterial blood
What does ṽ stand for?
Mixed venous blood (e.g pulmonary artery)
What are the missing values from the table?
What is the rate of diffusion across the membrane directly proportional to?
Partial pressure gradient
Gas solubility
Available surface area
What is rate of diffusion across the membrane indirectly proportional to?
The thickness of the membrane
When is the rate of diffusion of gas across the membrane most rapid?
Over short distances
Look at this slide
What is the surface area of an alveoli in emphysema?
Reduced surface area
What are the features of Fibrotic lung disease?
Thickened alveolar membranes slows gas exchange. Loss of lung compliance may decrease alveolar ventilation.
What are the features of pulmonary edema?
Fluid in interstitial space increases diffusion distance. Arterial pCO2 may remain normal due to higher solubility in water.
Describe asthma
Increased airway resistance decreases airway ventilation
Which picture represents fibrotic alveoli, normal alveoli and pulmonary oedema?
Fibrotic, normal, oedema
What is ventilation linked to?
Perfusion - (local blood flow L/min)
What is distribution of blood flow in the lung influenced by?
Hydrostatic pressure and alveolar pressure
Why is blood flow at the base of the lungs high?
Arterial pressure exceeds alveolar pressure and vascular resistance is therefore low.
Why is blood flow low at the at the apex of the lung? (in pulmonary capillaries?)
Arterial pressure is less than alveolar pressure. This compresses the arterioles and vascular resistance is increased.
What is the optimal condition for ventilation?
Ventilation = blood flow
Which of the mismatches has
- Under oxygenated blood
- Too much breathing taking place compared to the rate of blood flow
- Mismatch 2
- Mismatch 1
Where does majority of the mismatch take place?
Apex of the lung
Over 75% of the height the healthy lung performs quite well in matching blood and air
What happens if ventilaiton decreases in a group of alveoli?
PCO2 increases and PO2 decreases. Blood flowing past those alveoli does not get oxygenated.
What decreased PO2 around underventilated alveoli cause?
Constricts their arterioles, diverting their blood to better ventilated alveoli
Constriction in response to hypoxia is particular to pulmonary vessels (systemic vessels dilate)
What does increased PCO2 cause?
Mild bronchdilation
Ultimately this response increases perfusion and, to a lesser extent, decreases ventilation, bringing the ratio back towards 1.What happens when you get ventilation > blood flow?
What is shunt?
Shunt is a term used to describe the passage of blood through areas of the lung that are poorly ventilated (ventilation << perfusion
Shunt is the opposite of alveolar dead space
What are is alveolar dead space?
Alveolar Dead Space refers to alveoli that are ventilated but not perfused.
What is anatomical dead space?
Anatomical Dead Space refers to air in the conducting zone of the respiratory tract unable to participate in gas exchange as walls of airways in this region (nasal cavities, trachea, bronchi and upper bronchioles) are too thick.
What is physiological dead space?
Physiological Dead Space = Alveolar DS + Anatomical DS
What does the low pressure circuit cause?
More susceptible to the effects of gravity and this gives rise to a great degree of variability in blood flow within the lung.
Why are the overall rates of equilibrim between O2 and CO2 similar? Despite the fact CO2 is more soluble?
Because of the greater pressure difference for O2
