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Pulmonary Circulation Characteristics


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Pulmonary Circulation Characteristics. Low Resistance /Pressure The specific structure(s) primarily responsible for the majority of control of resistance in the resting state is controversial.

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Pulmonary Circulation Characteristics

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Pulmonary circulation characteristics l.jpg

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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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


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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


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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

    • HistamineVenular 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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120

100

Vascular Resistance

(cmH2O/L•min-1)

80

60

200

50

100

150

Lung Volume (ml)


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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 ControlDecreased PAO2 causes vasoconstriction. Advantage: blood is shunted away from poorly ventilated alveoli.

  • Surrounding Pressure

    • Alveolar

    • Interstitial (<0)


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The Starling Resistor Concept

Pulmonary

Circulation


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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)


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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