Physiology of Respiration Part IV Prof. Dušan M. Mitrović, M.D., Ph.D

Blood flow and Metabolism How the pulmonary Circulation Removes Gas From the Lung and Alters Some Metabolites

Systemic and Pulmonary Circulation

Pressures Around Pulmonary Blood Vessels Note: around alveaolar vessels pressure is alveolar The pressure difference between the isside and outside of the capillaries is called transmural pressure

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

Pulmonary Vascular Resistance input pressure – output pressure Vascular resistance = 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 increase in caliber of vessels opening previously closed vessels

Effects of lung volume on pulmonary vascular resistance when 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 flow

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

Distribution of Blood Flow

Measurement of the distribution of blood flow in the upright human lung with radioactive xenon Disolved xenon is envolved into alveolar gas from pulmonaru capilaries

Regional perfusion and gravity PPA blood pressure in the pulmonary artery PPV blood pressure in pulmonary vein Ppc pericapillary pressure PL,is interstitial pressure in the lung tissue Qc capillary blood flow

The Starling resistors Rubber tube When chamber pressure exceeds downstream pressure (A), flow is independent of downstream pressure. When downstream pressure exceeds chamber pressure (B), flow is idetermined by The upstream-downstream pressure difference.

Regional capillary blood volume

Active control of circulation Hypoxic pulmonary vasoconstriction

Water Balance in the Lung

Lymph and fluid movement in the lung

Metabolic Function of the Lung Peptides Angiotenzin I Converted to angiotensin II by ACE Bradykinin Up to 80% inactivated Amines Serotonin Almost completely removed Noradrenalin Up to 30% removed Arachidonic acid metabolites Prostaglandin E2 and E2a Almost completely removed Leukotriens Almost completely removed

Two pathways of arachidonic acid metabolism Membrane-bound phospholipid Phospholipase A2 Arachidonic acid Cyclooxygenase Lipoxygenase Prostaglandins, Tromboxane A2 Leukotriens