Lectures on respiratory physiology Pulmonary Blood Flow

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

P in P out FLOW VASCULAR RESISTANCE = ELECTRICAL RESISTANCE = FLOW INPUT PRESSURE – OUTPUT PRESSURE CURRENT INPUT VOLTAGE – OUTPUT VOLTAGE Comparison of vascular and electrical resistance

Effects of increased pressures on vascular resistance

Recruitment and distension of capillaries

P ulmonary capillary has a very thin wall

Demonstration of recruitment

Demonstration of distension

Effect of lung volume on resistance

FICK PRINCIPLE Vo 2. vo 2 - C Ca o2o2 Vo 2. Q (. = Ca o2o2 vo 2 - C - ) Q. = Vo 2. Ca o2o2 vo 2 - C - Measurement of total pulmonary blood flow

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 PO 2

Alveolar gas is very close to the wall of the artery

Low alveolar PO 2 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 E 1, E 2, and F 2 alpha. Norepinephrine is also partially inactivated Not affected: Examples include epinephrine, prostaglandins A 1 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.