Lectures on respiratory physiology Pulmonary Blood Flow Pulmonary and systemic circulations Alveoli with capillaries Compression of capillaries Pulmonary capillary has a very thin wall Small pulmonary vein Alveolar and extra-alveolar vessels Comparison of vascular and electrical resistance Pin Pout FLOW INPUT PRESSURE – OUTPUT PRESSURE VASCULAR RESISTANCE = FLOW INPUT VOLTAGE – OUTPUT VOLTAGE ELECTRICAL RESISTANCE = CURRENT Effects of increased pressures on vascular resistance Recruitment and distension of capillaries Pulmonary capillary has a very thin wall Demonstration of recruitment Demonstration of distension Effect of lung volume on resistance Measurement of total pulmonary blood flow . Vo2 FICK PRINCIPLE C vo Ca o 2 2 . . - ) Vo2 = Q ( Ca o - C vo 2 2 . . Vo2 Q = Ca o - C vo 2 2 Uneven distribution of blood flow Effects of change of posture and exercise Normal distribution in isolated lung Effect of reducing pulmonary artery pressure Effect of raising pulmonary venous pressure Three zone model of distribution of blood flow Compression of capillaries Three zone model of distribution of blood flow Model of a Starling resistor Three zone model of distribution of 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 Effect of breathing 10% oxygen Effect of reducing the alveolar PO2 Alveolar gas is very close to the wall of the artery Low alveolar PO2 causes 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 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.