Lectures on respiratory physiologyLectures on respiratory physiology

Pulmonary Blood FlowPulmonary 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

Pin

Pout

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

Pulmonary capillary has a very thin wall

Demonstration of recruitment

Demonstration of distension

Effect of lung volume on resistance

FICK PRINCIPLEVo2

.

vo2-C

Cao2

Vo2

.Q (.

= Cao2 vo2-C- )

Q.

=Vo2

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Cao2 vo2-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 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.