WEST ZONES of the Lung

• Zone 1
• Zone 2
• Zone 3
• Zone 4
• Fundamentals
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Zone 1 (wasted ventilation)

V/Q is elevated.

The conditions in Zone 1 are:

• Alveolar pressure exceeds pulmonary arterial & venous capillary pressure

• Little gas exchange takes place
• Blood flow is limited & probably cyclical (i.e. only systolic, and dependent on the phase of the respiratory cycle)

Also: intrapleural pressure in Zone 1 is lower than that in the other zones. Mine: Gravity causes the top of the lung (visceral pleura) to peel away & fall from the parietal pleura, causing increased space which causes a drop in intrapleural pressure.

Ventilation is decreased because the alveoli are already quite distended--thus CAN'T be expanded more to provide more ventilation.

How to create Zone 1 condition:

• Positive pressure ventilation
• Hypovolemia or Hemorrhagic Shock

Zone 2

Zone 3 (wasted perfusion)

V/Q is reduced.

Ventilation is increased because the alveoli are small & squished--& thus CAN be expanded more to provide more ventilation.

Zone 4

Fundamentals

4 concepts to understand the zones of the lung:  1. Ohms law; 2.Poiseuille’s Law; 3. Starling resistor; 4. Gravity

   I = flow   R = resistance  F = flow           

Video:

4 Fundamental Concepts for West Lung Zones  excerpted from CaseMed Minute

Zones of the Lung: by CaseMed Minute