Updated: 1/17/2016

Distribution of Pulmonary Blood Flow

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                           Pulmonary Blood Flow
  • Supine
    • distribution of pulmonary blood flow in lung is nearly uniform
  • Standing
    • distribution of pulmonary blood flow in lung is uneven due to effects of gravity
  • Zone 1
    • PA ≥ Pa > PV
      • PA = alveolar pressure
      • Pa = arterial pressure
      • PV = venous pressure
    • PA ≥ Pa
      • pulmonary capillaries may be compressed by high alveolar pressure
        • reduces blood flow
      • in normal lung, Pa is just high enough to prevent compression and to permit perfusion
        • ↓ Pa PA > Pa pulmonary capillary compression and occlusion
          • e.g., hemorrhage
          • no zone 1 perfusion
            • no gas exchange → ↑ physiologic dead space
        • PA PA > Pa pulmonary capillary compression and occlusion
          • e.g., positive pressure ventilation
          • no zone 1 perfusion
            • no gas exchange → ↑ physiologic dead space
  • Zone 2
    • Pa > PA > PV
    • PA > PV
      • blood flow driven by difference between arterial pressure and alveolar pressure
  • Zone 3
    • Pa > PV > PA
    • PV > PA
      • blood flow driven by difference between arterial pressure and venous pressure
    • greatest number of pulmonary capillaries open
    • highest blood flow
 

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