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Cardiac Physiology (III)

Cardiac Physiology (III). A. R üç han Akar Ankara University School of Medicine December- 2003. Coronary Circulation. Coronary Blood Flow. coronary blood flow: 250 ml/min 5% of resting cardiac output 60-80 ml blood/100g tissue/min entirely during diastole

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Cardiac Physiology (III)

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  1. Cardiac Physiology(III) A. Rüçhan Akar Ankara University School of Medicine December- 2003

  2. Coronary Circulation

  3. Coronary Blood Flow • coronary blood flow: 250 ml/min • 5% of resting cardiac output • 60-80 ml blood/100g tissue/min • entirely during diastole ~ aortic diastolic pressure minus LVDP ~ duration of diastole • pressure < 150 mmHg • oxygenated by superb membrane oxygenator-”the lungs”

  4. Cerebral Blood Flow • Cerebral blood flow: 750 ml/min • 15% of resting cardiac output • 50-55 ml blood/100g tissue/min

  5. * The peak left coronary flow occurs at the end of isovolumetric relaxation * Left coronary blood flow Right coronary blood flow

  6. mitochondria cellular pO2 < 5mmHg within seconds oxidative phosporilation stops cytosol anaerobic glycolysis glycogen glucose-6-phosphate pyruvate lactate cellular acidosis depletion of ATP Cessation of Myocardial Blood Flow

  7. Depletion of ATP < 50% of Normal Level- irreversible lethal cell injury • glycolysis is blocked • increasing cellular acidity • protein denaturation • structural, enzymatic, nuclear changes

  8. Blood Vessel

  9. Measurement of Cardiac Output Fick Principle

  10. The Fick Principle . VO2 CaO2 – CvO2 Q = – Q: cardiac output VO2: O2 consumption CaO2:arterial O2 content CvO2: mixed venous O2 content

  11. Blood Vessel • Intima primarily the endothelial lining • Media vascular smooth muscle, collagen, elastin • Adventitia connective tissue

  12. Vascular Endothelium Vasodilators Vasoconstrictors Nitric Oxide Prostacyclin Endothelium-derived hyperpolarizing factor Bradykinin Endothelin-1 Angiotensin II Wilson SH, Lerman A. Heart Physiology and Pathophysiology, Academic Press (edited by Sperelakis N.) 473-480

  13. L-Arginine is converted to NO by the enzyme nitric oxide synthase (NOS)

  14. Nitric Oxide (NO)Function • Vasodilator • Inhibitor of vascular smooth muscle cell proliferation • Inhibitor of platelet adherence/aggregation • Inhibitor of leukocyte/endothelial interactions

  15. Endothelin-1(ET-1) • Peptide first sequenced in 1988 • Most potent vasoconstrictor in humans • Maintenance of basal arterial vasomotor tone • Strong chemoattractant for circulating monocytes and macrophage activation “proatherogenic”

  16. Endothelial Dysfunction • Imbalance of endothelium-derived relaxing and contracting factors Atherosclerotic risk factors Decreased NO bioavailability Increased levels of ET-1

  17. Functional Classification of Vessel Wall • elastic arteries • muscular arteries • resistance vessels • capillaries (exchange vessels) • venules (capacitance vessels) JR Levick, 1995 An Introduction to Cardiovascular Physiology Butterworth-Heinemann

  18. Elastic Arteries • aorta, pulmonary artery and major branches • diameter = 1-2 cm • tunica media is rich in elastin (extensible) • collagen (prevents overdistension)

  19. intima AORTA Elastic fibers Smooth muscle media adventitia Bergman RA, Afifi AK, Heidger PM Atlas of Microscopic Anatomy, 1989 W.B. Saunders Company

  20. Conduit (Muscular) Arteries • diameter = 1mm-1cm • popliteal, radial, cerebral, coronary arteries • tunica media is thicker, contains more smooth muscle • rich autonomic nerve supply (contraction and relaxation)

  21. Resistance Vessels • main resistance to blood flow resides in the; • smallest, terminal arteries (diameter = 100-500mm) • arterioles (< 100mm) “single layer of muscle in the media” • richly innervated by vasoconstrictor nerve fibres • actively regulate local blood flow to match local demand

  22. Capillaries (Exchange vessels) • diameter: 4-7mm • wall: single layer of endothelial cells • wall thickness = 0.5mm • large cross-sectional area • slow blood velocity • red cell transit time = 1-2 sec

  23. Arteriovenous Anastomosis • shunt vessels ( diameter = 20-135mm) • connect arterioles to venules, bypassing the capillaries • skin, nasal mucosa • temperature regulation

  24. The Veins“Capacitance Vessels” • diameter 50-200mm • thin wall • in limb veins, intima possesses pairs of valves • low resistance to flow • storing large volumes of blood under low pressure • ~ 60-70% of the circulating blood volume

  25. Distribution of blood volume in a resting man ( 5.5 litres) Folkow B, Neil E. 1971, Oxford University Press, London

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