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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 Lectures on respiratory physiology
Comparison of vascular and electrical resistance Pin Pout FLOW INPUT PRESSURE – OUTPUT PRESSURE VASCULAR RESISTANCE = FLOW INPUT VOLTAGE – OUTPUT VOLTAGE ELECTRICAL RESISTANCE = CURRENT
Measurement of total pulmonary blood flow . Vo2 FICK PRINCIPLE - C vo2 Ca o2 . . - = - Ca Q ( C Vo2 ) o2 vo2 . . Vo2 = Q - - Ca C o2 vo2
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
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 • 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.