Questions and Answers
What is the principle of West zones?
Capillary blood flow to alveoli is dependent on pressure of gas in alveolus.
What are the 3 West Zones?
Zone 1: PA > Pa > Pv; Zone 2: Pa > PA > Pv; Zone 3: Pa > Pv > PA.
Describe the VQ relationship throughout the lungs.
The V/Q ratio is higher in zone 1 (apex) than in zone 3 (base) due to higher ventilation and perfusion at the base.
When VP > 1 and 1, it indicates ___ = wasted ventilation/increased alveolar dead space.
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What is a shunt?
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What are the causes of a VQ mismatch?
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Study Notes
West Zones
- Capillary blood flow to alveoli depends on alveolar gas pressure.
- There are three distinct West Zones that describe blood flow and ventilation dynamics in the lungs.
West Zone Descriptions
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Zone 1: PA > Pa > Pv
- Alveolar pressure exceeds both arterial and venous pressures, leading to vessel collapse and lack of perfusion.
- Considered as dead space; does not occur under normal lung conditions.
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Zone 2: Pa > PA > Pv
- Systolic pulmonary arterial pressure surpasses alveolar pressure, but diastolic does not permit continuous blood flow only during systole.
- Results in both dead space and wasted ventilation; reflects normal lung behavior above the hilum.
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Zone 3: Pa > Pv > PA
- Both arterial and venous pressures exceed alveolar pressure due to gravity, allowing continuous blood flow.
- Represents normal lung behavior below the hilum.
Ventilation/Perfusion Relationship
- V/Q ratio is highest in Zone 1 (apex of the lung) where perfusion is minimal.
- V/Q ratio is lowest in Zone 3 (base of the lung) due to highest ventilation and perfusion.
V/Q Ratio Implications
- A V/Q ratio greater than 1 indicates inadequate perfusion, leading to wasted ventilation and increased alveolar dead space.
- A ratio of 25% likely suggests the presence of West Zone 3 conditions.
Shunt Definition
- Occurs when poorly ventilated alveoli are perfused normally, resulting in a V/Q ratio of 1.
- Conditions that can cause shunting include:
- Cardiovascular shock, where blood flow to the lungs is impaired.
- Emphysema, characterized by enlarged alveoli with reduced surface area and fewer capillaries.
- Pulmonary embolism, where blood flow is obstructed by a clot.
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Description
Explore the dynamics of capillary blood flow to alveoli in the lungs, focusing on the three distinct West Zones. Understand how alveolar gas pressure impacts blood perfusion and the ventilation/perfusion relationship in each zone. This quiz will enhance your knowledge of respiratory physiology.
