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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 capillary has a very thin wall




Comparison of vascular and electrical resistance

Pin

Pout

FLOW

INPUT PRESSURE – OUTPUT PRESSURE

VASCULAR RESISTANCE =

FLOW

INPUT VOLTAGE – OUTPUT VOLTAGE

ELECTRICAL RESISTANCE =

CURRENT




Pulmonary capillary has a very thin wall





Measurement of total pulmonary blood flow

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FICK PRINCIPLE

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Q (

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Vo2

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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





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.


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