Pulmonary Circulation Characteristics

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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

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Influences on resistance
Pulmonary Circulation

• 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

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Perfusion
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Influences on resistance
Pulmonary Circulation

• 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

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Influences on resistance
Pulmonary Circulation

• 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 (lt0)

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The Starling Resistor Concept
Pulmonary Circulation
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Pulmonary Circulation
Arterial (Pa)
Alveolar (PA)
Venous (Pv)
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Pulmonary Circulation