Coronary Blood Flow PDF

Coronary Blood Flow Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Describe the characteristics of the coronary blood vessels. Demonstrate the phasic supply of blood to the heart during systole and diastole. Explain the relation of coronary blood flo...

Coronary Blood Flow Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Describe the characteristics of the coronary blood vessels. Demonstrate the phasic supply of blood to the heart during systole and diastole. Explain the relation of coronary blood flow and the cardiac cycle. Describe factors affecting coronary blood flow. Coronary blood vessels They are the blood vessel that supply the heart. They are right and left coronary arteries that arise from the aorta just above the aortic valve. Right coronary artery supply Right Atrium (S.A, A.V Nodes) Right ventricle Posterior interventricular septum Posterior part of the left ventricle  Left coronary artery supply Left atrium Left ventricle (Anterior and lateral walls) Anterior interventricular septum Major venous drainage is coronary sinus which opens into right atrium Characteristics of the Coronary vessels 1- There orifices of coronary vessels are always open by the current of blood flow. 2- Large coronary arteries are present in the epicardium. These arteries then arborize into smaller branching forming epicardial and subendocardial capillary network. 3- The capillary density is extremely high in the heart, exceeding 3000/mm2, as compared with 400/mm2 in skeletal muscle. What is the effect of systole in the blood flow of subendocardial plexus? It will be reduced because the intramuscular coronary vessels are compressed greatly by ventricular muscle contraction. So, subendocardial portion of the left ventricle is the most common site of myocardial ischemia and infarction Characteristics of the Coronary vessels 4- Coronary arteries are Functionally END arteries, There is no or few anastomosis between large arteries. So , with atherosclerosis, when the coronary vessel is narrowed →decrease blood supply with exertion producing severe angina pain. Characteristics of the Coronary vessels 5- High rate of O2 consumption at rest , energy production in the heart completely aerobic (need O2). 6- High arterial O2 extraction ratio= 75% (Very low O2 reserve) N.B: O2 extraction is ratio of O2 consumption to O2 delivery. O2 extraction = O2 Consumption( ArterialO2-Venous O2) O2 delivery = 19.5 - 5.5 = 75% 19.5 So, during exercise, any extra O2 requirements can only be obtained by increasing the coronary blood flow. Coronary blood Flow The coronary blood flow in the resting person = 70 ml/min/100 g or = 225 ml/min, (5% of the total cardiac output) During exercise: the coronary blood flow increases 3-fold to 4-fold. = 1000ml/min Phasic Changes in Coronary Blood Flow During Systole and Diastole Normally: Blood flow increased to all the body tissue during systole and decreased during diastole. Left Ventricle During systole, the coronary blood flow in the left ventricle muscle falls to a low value due to strong compression of the intramuscular blood vessels by the left ventricular muscle during systolic contraction. During diastole, the cardiac muscle relaxes and no longer obstructs blood flow through the left ventricular muscle capillaries, so blood flows rapidly during all of diastole. Phasic Changes in Coronary Blood Flow During Systole and Diastole Blood flow to the right and left atria, right ventricle also undergo phasic changes during the cardiac cycle but, because the force of contraction of the right ventricular muscle is far less than that of the left ventricular muscle, the blood flow increase during systole and decrease during diastole. What is the relation of coronary blood flow and the cardiac cycle? Right coronary flow Left coronary flow Blood flow increases in rapid ejection phase (systole) Blood flow increases in Isometric relaxation phase (diastole) Factors affecting Coronary blood flow Metabolic factors Autoregulation Mechanical factors Neural factors Hormonal factors Metabolic factors The primary control of coronary blood flow is muscle metabolism. ↑Myocardial activity →↑metabolites → Vasodilation of coronary blood vessel → increase coronary blood flow. Metabolites : Increased adenosine Increased nitric oxide Opening of ATP-sensitive potassium (KATP) channels. CO2, H+, and prostaglandins Autoregulation  At rest, autoregulation maintains a consistent blood flow to the heart even when the mean arterial pressure changes between 60-160 mm Hg.  Mechanism: depends on myogenic activity.  Decrease ABP → Decreased coronary flow → coronary artery dilation → increase coronary flow back to normal V.D  Increase ABP → increased coronary flow → coronary artery vasoconstriction → decrease coronary flow back to normal V.C Mechanical factors Relation of the coronary blood flow to cardiac cycle. Left ventricular coronary flow Isometric relaxation (Diastole) Right ventricular coronary flow Rapid ejection (Systole) Neural factors Sympathetic stimulation DIRECTLY constrict the coronaries through stimulation of α adrenergic receptors BUT it increases the metabolites causing INDIRECT VASODILATATION of the coronaries. Parasympathetic stimulation causes mild vasodilatory effect on coronary vessels BUT it decrease the metabolite causing vasoconstriction. Hormonal factors Catecholamines increase cardiac activity → increase metabolites → coronary vasodilation (Same as sympathetic stimulation). Angiotensin II and ADH (vasopressin) → direct coronary vasoconstriction → decrease coronary blood flow. V.D Review Questions Blood flow in the left coronary vessels is maximal during which of the following periods? A. B. C. D. E. During atrial diastole During ventricular contraction During ventricular diastole No maximal flow; flow is same throughout the cardiac cycle Systole The heart extracts how much oxygen from the coronary arteries at rest? A. B. C. D. E. 10% 25% 50% 75% 100% Summary Describe the characteristics of the coronary blood vessels. Demonstrate the phasic supply of blood to the heart during systole and diastole. Explain the relation of coronary blood flow and the cardiac cycle. Describe factors affecting coronary blood flow.