CV System - Coronary Circulation E&P2 PDF

Heart’s Blood Supply - Heart has its own circulatory network, the coronary circulation, that arises from heart’s top portion - Right and left coronary arteries - Greatest blood volume flows in left coronary artery: - Feeding left atrium and left ventricle, and right ventricle - Blood leaves tissues...

Heart’s Blood Supply - Heart has its own circulatory network, the coronary circulation, that arises from heart’s top portion - Right and left coronary arteries - Greatest blood volume flows in left coronary artery: - Feeding left atrium and left ventricle, and right ventricle - Blood leaves tissues of left ventricle through coronary sinus and right ventricle from anterior cardiac veins - Both dump into right atrium - Normal blood flow to myocardium at rest = 200-250 m:/mm (5% total output) Myocardial Oxygen Supply and Use - At rest: mmyocardium extracts 70-80% of O2 from blood in coronary vessels - Proportionate increase in coronary blood flow during exercise provides sole mechanism to increase myocardial O2 supply - 2 factors increase myocardial blood flow: - 1. Increase metabolism dilates coronary vessels - 2. Increase aortic pressure during exercise forces a proportionately greater volume of blood into coronary circulation Impaired Myocardial Blood Supply - Myocardium depends on adequate O2 supply b/c it has limited anaerobic capacity - Can’t make extensive switch - Extensive vascular perfusion supplies at least 1 capillary to each of the heart’s muscle fibers - Tissue hypoxia provides a potent stimulus to myocardial blood flow - Can produce chest pains (angina pectoris) - Exercise provides effective way to evaluate adequacy of myocardial blood flow - A blood clot in a coronary vessel can impair normal heart function, leading to a myocardial infarction → heart tissue will die due to lack of oxygen Rate-Pressure Product (RPP) - RPP: estimate of myocardial workload and VO2 - Computed from product of peak SBP measured at brachial artery and heart rate - Index of relative cardiac work - Relates closely to directly measured myocardial VO2 and coronary blood flow in healthy subjects over a wide range of exercise intensities - RPP = SBP x HR - Ranges from 6000 at rest to greater/equal to 40,000 during exercise, depending on intensity and mode Myocardial Metabolism - Rest: fat/lipids as fuel - Moderate: glucose and lactate used more - Intense exercise: lactate as its oxidized