Gravitational Gradients

Gravitational Gradients

Jud W. Gurney, MD, FACR



  • Distribution of disease not a random process but end result of interaction between pathologic process with its environment

    • Gravity alters pulmonary physiology and creates differing regional environments, especially in upright lung

  • Ventilation (V) upright lung

    • Normal 3x difference from top to bottom of lung due to effect of gravity on intrapleural pressure, transpulmonary gradients, and alveolar size

    • Branching pattern of airways important in distribution of particulate material suspended in inhaled air

      • Turbulent airflow in large upper airways (1st 6 generations) directs particles > 5 µm in diameter against ciliated airways where they can be removed from lung

      • Particles < 5 µm in diameter can deposit in respiratory bronchioles within centrilobular portion of lobule

      • Particles tend to follow straightest pathway through lung, which is to lung periphery

    • Determines distribution of inhaled insults, which acutely affect lung

  • Perfusion (Q) upright lung

    • Normal 18x difference from top to bottom of lung due to effect of gravity on low pressure pulmonary arterial system

      • Main pulmonary artery inclined toward left upper lung; jet effect across pulmonic valve increases blood flow 10% above similar regions in right upper lobe

    • Zonal blood flow (according to West model)

      • Blow flow determined by pulmonary arterial (pa), pulmonary venous (pv), and alveolar pressure (pA)

      • Zone 1: pA > pa > pv, capillaries collapsed, no blood flow, does not occur in normal lung but in hypotensive patient on mechanical ventilation and PEEP may develop zone I conditions in nondependent lung

      • Zone 2: pa > pA > pv, blood flow not determined by gradient between arterial and venous pressure but gradient between arterial and alveolar pressure and may produce erroneous clinical pressure readings from wedged Swan-Ganz catheter

      • Zone 3: pa > pv > pA, blood flow determined by arterial venous pressure gradient

    • Determines distribution of hydrostatic (cardiogenic edema) and blood borne insults (hematogenous metastases)

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Sep 20, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Gravitational Gradients
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