Questions and Answers
What is the main point of West Zones or dividing up the lungs by zone?
The upright human lung can be divided into the 3 Zones of West, Zones I, II and III, based on the relationship between pulmonary arterial pressure (Ppa), alveolar pressure (PA) and pulmonary venous pressure (Pv).
What is the VQ ratio in Zone 1?
It is decreased. VQ > 0.8.
Alveoli in this zone would be expected to have the highest PO2 and lowest PCO2 of any zone.
Zone I.
In which zone would alveoli be most distended?
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What determines the perfusion of Zone 2 or the waterfall region?
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In this zone, the vein diameter is the greatest and the alveolar size is the smallest.
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What is the VQ ratio in Zone 3?
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In which West zone is PaO2 most decreased and PaCO2 most increased?
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Where should the PA catheter be placed to reflect LV pressure most accurately?
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The zone with the lowest radioactivity per unit lung volume following the injection of radioactive xenon into the right ventricle is?
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The zone in which individual alveoli are likely to have the smallest volume at end expiration is?
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Alveoli in this zone would be expected to have the highest PO2 and lowest PCO2 of any zone.
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In which lung zone would a / ratio of over 2, a low or intermittent blood flow, and a capillary hydrostatic pressure close to atmospheric pressure most likely be observed?
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Study Notes
Overview of West Zones
- The upright human lung is divided into three zones: Zone I, Zone II, and Zone III, based on pulmonary arterial pressure (Ppa), alveolar pressure (PA), and pulmonary venous pressure (Pv).
- Zones help in understanding the physiological variations in blood flow, ventilation, and gas exchange within the lung.
Zone I
- Characterized by higher alveolar ventilation relative to perfusion, leading to over-ventilation (V/Q > 0.8).
- Alveoli have the highest PO2 and lowest PCO2 among the zones.
- Alveoli in this zone are most distended, indicating reduced pulmonary blood flow.
- Identified as the zone with the lowest radioactivity per unit lung volume post-radioactive xenon injection.
- Intrapleural pressure is closest to atmospheric pressure at normal end expiration.
- Can exhibit a V/Q ratio greater than 2 with intermittent blood flow and low capillary hydrostatic pressure.
Zone II
- Perfusion is determined by the difference between arterial pressure (Pa) and alveolar pressure (PA).
- Represents a transition zone between high ventilation and low perfusion.
Zone III
- Characterized by increased perfusion where Pa is greater than Pv, which in turn is greater than PA.
- Contains the largest vein diameter and smallest alveolar size at end expiration.
- V/Q ratio is approximately 0.8, indicating that perfusion exceeds ventilation.
- Alveoli exhibit decreased PO2 and increased PCO2 due to collapse.
- The best location for PA catheter placement to accurately reflect left ventricular pressure, due to the greater blood flow in this zone.
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Description
Test your knowledge of the West Zones in lung physiology with these flashcards. Understand the relationship between pulmonary pressures and the VQ ratio across the zones. Perfect for students of physiology or medical sciences.
