West’s Zones




Fig. 76.1






  1. 1.


    What does the above image depict, and what are the pressure profiles in the zones?

     

  2. 2.


    Describe the factors that affect pulmonary vascular resistance [1].

     

  3. 3.


    What are the clinical implications of the zones of west?

     



Answers


  1. 1.


    The image above depicts West’s zones of the lung which describe the effects of gravity and the differing pressures within the alveoli, pulmonary arteries, and veins on ventilation and perfusion.

    When one views the vascular resistance in an upright individual, three lung perfusion zones are identified. The hydrostatic pressure in the pulmonary vascular system of an upright individual varies from the apex to the base of the lungs and therefore the perfusion characteristics vary as well. Pulmonary arterial pressure is 5 mmHg at the apex and 25 mmHg at the base, and pulmonary venous pressure is −5 mmHg at the apex and +15 mmHg at the bases.

    Zone 1 is not seen in normal lungs. It may be seen in positive pressure ventilation or after hemorrhage. Alveolar pressure exceeds pulmonary vascular pressures. Hence the pulmonary vessels are collapsed, and no flow occurs causing alveolar dead space.

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Sep 23, 2017 | Posted by in Uncategorized | Comments Off on West’s Zones
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