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Pulmonary Blood Flow. Lectures on respiratory physiology. Pulmonary and systemic circulations. Alveoli with capillaries. Compression of capillaries. P ulmonary capillary has a very thin wall. Small pulmonary vein. Alveolar and extra-alveolar vessels.

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Pulmonary blood flow

Pulmonary Blood Flow

Lectures on respiratory physiology





Pulmonary blood flow

Pulmonary capillary has a very thin wall




Pulmonary blood flow

Comparison of vascular and electrical resistance

Pin

Pout

FLOW

INPUT PRESSURE – OUTPUT PRESSURE

VASCULAR RESISTANCE =

FLOW

INPUT VOLTAGE – OUTPUT VOLTAGE

ELECTRICAL RESISTANCE =

CURRENT




Pulmonary blood flow

Pulmonary capillary has a very thin wall





Pulmonary blood flow

Measurement of total pulmonary blood flow

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FICK PRINCIPLE

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Vo2

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Non gravitational causes of uneven blood flow
Non-gravitational causes of uneven blood flow

  • Random variations in the resistance of blood vessels

  • Some evidence that proximal regions of an acinus receive more blood flow than distal regions

  • In some animals some regions of the lung have an intrinsically higher vascular resistance





Pulmonary blood flow

Low alveolar PO2 causes vasoconstriction


Evolutionary pressure for hypoxic pulmonary vasoconstriction
Evolutionary pressure for hypoxic pulmonary vasoconstriction

  • Pulmonary blood flow in the fetus is only about 15% of the cardiac output

  • Most of the output of the right ventricle bypasses the lung through the ductus arteriosus

  • The pulmonary vascular resistance is high because of hypoxic vasoconstriction in the very muscular pulmonary arteries

  • Immediately after birth, and pulmonary blood flow must increase dramatically

  • The great fall in pulmonary vascular resistance is due mainly to the release of hypoxic vasoconstriction

  • In addition the ductus arteriosus gradually closes


Substances metabolized by the lung
Substances metabolized by the lung

  • Biological activation: Angiotensin I is converted to the vasoconstrictor, angiotensin II via ACE

  • Biological inactivation:. Examples include bradykinin, serotonin, prostaglandins E1, E2, and F2 alpha. Norepinephrine is also partially inactivated

  • Not affected: Examples include epinephrine, prostaglandins A1 and A2, angiotensin II and vasopressin.

  • Metabolized and released: Examples include the arachidonic acid metabolites - the leukotrienes, and prostaglandins.

  • Secreted: Immunoglobulins, particularly IgA, in bronchial mucus.