Describe the ventilation / perfusion (V/Q) relationships in the upright lung according to West’s zones (40%). Explain the physiological mechanisms responsible for these relationships (60%).
This is a core aspect of respiratory physiology, and a detailed understanding of this topic is crucial to the daily practise of intensive care. As such the answers were expected to be detailed. Strong answers included precise descriptions of the zones of the lung as described by West and related these to the V/Q relationship in the upright lung. Generally, most candidates scored well in this section. Diagrams were of varying value. However, an impression from the examiners was that candidates spent too much time on this first section and ran out of time for a detailed answer in the second section. The answers to the second section seemed rushed and were often lacking in detail with many incorrect facts. This question highlights the importance of exam technique preparation in the lead up to the written paper.
VQ relationships in West's zones:
Physiological mechanisms responsible for this:
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Glenny, Robb W., Steven McKinney, and H. Thomas Robertson. "Spatial pattern of pulmonary blood flow distribution is stable over days." Journal of Applied Physiology 82.3 (1997): 902-907.