Coronary Blood Flow and Ischemic heart Disease Flashcards Preview

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Flashcards in Coronary Blood Flow and Ischemic heart Disease Deck (17):

determinants of metabolic needs

wall stress

heart rate



double product index of oxygen demand

HR x peak systolic BP = MVO2

MVO2 = CBF x (A-V)O2


physiological factors governing coronary blood flow

flow = driving pressure/resistance

coronary flow = PAo/Rcoronary


components of coronary resistance

conduit artery resistance (usually small)

microvascular resistance (autoregulatory resistance)

compressive resistance


conduit artery resistance

normally very small

can be affected by endothelial and autonomic factors

increased when coronary artherosclerosis narrows the arterial lumen


microcirculatory resistance

primary mechanism by which flow adjusts to demand, and by which flow can be maintained constant when arterial pressure changes

relates to caliber of arterial microvessels and changes modestly in response to stimuli

normally high under basal conditions, there is a large reserve capacity for vasodilation

adjusted on a local basis


What governs R2?

metabolic factors such as adenosine and PO2

endothelial factors - EDRF (NO), endothelial-derived hyperpolarizing factor (EDHF), prostacyclins, endothelins

neurohormonal factors - autonomic nervous system and circulating vasoactive agents, alpha-adrenergic vasoconstriction and beta-adrenergic vasodilation


Endothelial-derive drelaxing factor (EDRF or NO)

synthesized continuously by coronary vascular endothelium, particularly microvessels > 100 um

rate of production varies (directly) with flow (local shear stress)

exerts a tonic vasodilating influence on R2

has similar but smaller effects on conduit vessels


compressive resistance

results from compression of coronary blood vessels during systole

causes flow during systole to be only a small fraction of that during diastole



autoregulation of coronary blood flow

coronary microvascular resistance (R2) adjusts to keep flow at the level appropriate to myocrdial O2 demand


reactive hyperemia

the increase in coronary flow which follows a brief period of coronary artery occlusion


coronary flow reserve

the ratio of flow during maximum coronary vasodilation to flow under resting conditions


negative atherosclarotic narrowing

luminal narrowing


positive atherosclerotic narrowing

increased wall thickness - occurs before negative narrowing


dynamic factors affecting pressure and narrowing across a stenosis

endothelial products

ANS vasoconstriction

vasoactive agents

sudden increases: plaque fissuring, thrombus formation


coronary collateral circulation

develops frequently as the degree of stenosis becomes critical

provides modest degree of perfusion to areas in jeopardy


principles of coronary stenosis treatment

limit increases in myocardial O2 demand - minimize increases in systolic BP, heart rate

augment flow to ischemic areas - counter dynamic incresaes in stenosis severity, counter endothelial dysfunction, counter abnormal vasoconstriction, increase collateral flow, intervention