Physiology of RespirationPart IV

Prof. Dušan M. Mitrović, M.D., Ph.D

Blood flow and MetabolismBlood flow and Metabolism

How the pulmonary CirculationRemoves Gas From the Lung and Alters Some Metabolites

Systemic and Pulmonary Circulation

Pressures Around Pulmonary Blood VesselsPressures Around Pulmonary Blood Vessels

The pressure difference between the isside and outsideof the capillaries is called transmural pressuretransmural pressure

Note: around alveaolar vessels pressure is alveolar

Many alveoli and an extra-alveolar vessel with its perivascular sheet

Pulmonary Vascular ResistancePulmonary Vascular Resistance

Vascular resistance =input pressure – output pressure

blood flow

Fall in pulmonary vascular resistance as the pulmonary arterial or venous pressure is raised.

There are two mechanisms for the decrease in pulmonary vascular resistance that occurs as vascular pressures are raised

opening previouslyclosed vessels

increase in caliber of vessels

Effects of lung volume on pulmonary vascular resistance Effects of lung volume on pulmonary vascular resistance when the transmural pressure of capillaries is held constantwhen the transmural pressure of capillaries is held constant

At low lung volumes, resistance is high because the extraalveolar vessels become narrow.

At high volumes, the capillaries are stretched, and their caliber is reduced.

Assesment of the pulmonary blood flowAssesment of the pulmonary blood flow

Measurements of capillary blood flow by recording Measurements of capillary blood flow by recording nitrous oxide uptake in body plethysmograph nitrous oxide uptake in body plethysmograph

Distribution of Blood FlowDistribution of Blood Flow

Measurement of the distribution of blood flowMeasurement of the distribution of blood flowin the upright human lung with radioactive xenonin the upright human lung with radioactive xenon

Disolved xenon is envolved into alveolar gas from pulmonaru capilaries

Regional perfusion and gravityRegional perfusion and gravity

PPA blood pressure in the pulmonary arteryPPV blood pressure in pulmonary veinPpc pericapillary pressure

PL,is interstitial pressure in the lung tissueQc capillary blood flow

The Starling resistorsThe Starling resistors

When chamber pressure exceeds downstream pressure (A), flow is independent of downstream pressure.

Rubber tube

When downstream pressure exceeds chamber pressure (B), flow is idetermined by The upstream-downstream pressure difference.

Regional capillary blood volumeRegional capillary blood volume

Active control of circulationActive control of circulation

Hypoxic pulmonary vasoconstrictionHypoxic pulmonary vasoconstriction

Water Balance in the LungWater Balance in the Lung

Lymph and fluid movement in the lungLymph and fluid movement in the lung

Metabolic Function of the LungMetabolic Function of the Lung

PeptidesPeptides

Angiotenzin I Converted to angiotensin II by ACE

Bradykinin Up to 80% inactivated

AminesAmines

Serotonin Almost completely removed

Noradrenalin Up to 30% removed

Arachidonic acid metabolitesArachidonic acid metabolites

Prostaglandin E2 and E2 Almost completely removed

Leukotriens Almost completely removed

Two pathways of arachidonic acid metabolismTwo pathways of arachidonic acid metabolism

Membrane-bound phospholipid

Arachidonic acid

Leukotriens Prostaglandins,Tromboxane A2

Phospholipase A2

Lipoxygenase Cyclooxygenase