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Pulmonary Circulation Characteristics
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Pulmonary Circulation Characteristics

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  1. Pulmonary CirculationCharacteristics • Low Resistance /Pressure • The specific structure(s) primarily responsible for the majority of control of resistance in the resting state is controversial. • Resistance more evenly distributed, but majority of resistance is normally on the arterial side (upstream) of the the capillaries. • Thin-walled arterial system (relatively little smooth muscle) • Anatomical considerations • Vessels are surrounded by bags of gas and flexible interstitial fluid-filled regions • No true arterioles?? • Alveolar and extra-alveolar vessels respond to conditions differently

  2. Neural/Humoral: all the same players as in the periphery (but less effective) and a few with more specific actions Serotonin: Arterial side vasoconstriction Histamine: Venular side vaso(veno)constriction ***venous side can become dominant resistance Intravascular Pressure R 1/P recruitment (primary) distension Pulmonary Circulation Influences on resistance

  3. 300 200 Increasing Arterial Pressure (cmH2O/L•min-1) Pulmonary Vascular Resistance 100 Increasing Venous Pressure 0 10 20 30 40 Arterial or Venous Pressure (cm H2O) Perfusion

  4. Pulmonary Circulation Influences on resistance • Neural/Humoral:all the same players as in the periphery (but less effective) and a few with more specific actions • Serotonin: Aretrial side vasoconstriction • Histamine Venular side vaso(veno)constriction • Intravascular Pressure R 1/P • recruitment (primary) • Distension ***Thus, cardiac output is considered to be the primary determinant of pulmonary vascular resistance • Lung volume

  5. 120 100 Vascular Resistance (cmH2O/L•min-1) 80 60 200 50 100 150 Lung Volume (ml)

  6. Pulmonary Circulation Influences on resistance • Lung volume • Low Volume: extra-alveolar vessels are smaller, capillaries more open • High Volume: extra-alveolar vessels are pulled open; capillaries become defromed by stretch (more oval; higher resistance) * Lung volume effects on extra-alveolar vessels is lost with positive pressure ventilation. • PO2: Local Control Decreased PAO2 causes vasoconstriction. Advantage: blood is shunted away from poorly ventilated alveoli. • Surrounding Pressure • Alveolar • Interstitial (<0)

  7. The Starling Resistor Concept Pulmonary Circulation

  8. Zone 1 PA>Pa>Pv Zone 2 Pa>PA>Pv Distance Zone 3 Pa>Pv>PA Blood Flow Pulmonary Circulation Arterial (Pa) Alveolar (PA) Venous (Pv)

  9. Pulmonary Artery Pulmonary Circulation 60 Pulmonary Arterial 50 Catheter Tracing 40 mmHg 30 20 10 0 Left Atrial Pressure Tracing Pulmonary Capillaries Left Atrium Pulmonary Vein