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31 Cards in this Set
- Front
- Back
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What occurs to coronary circulation of the innermost (endocardial) layers of the heart during systole?
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They are compressed and blood flow is reduced
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True/False: Coronary arterys have few sizeable anastomoses between individual coronary artery branches.
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TRUE
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Define: The large coronary arteries and veins visible on the surface of th heart.
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Conduit vessels
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True/False: the Conduit vessels (arteries/veins) on the surface of the heart exercise a large influence on coronary flow rate.
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False; the arterioles they supply exercise the strong influence
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Define: tiny, thick-walled muscular tubes which determine the rate of passage of blood through the coronary circulation.
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Coronary resistance vessels
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True/False: The heart extracts nearly all of the oxygen from circulation.
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TRUE
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The Rate of myocardial oxygen consumption (in a normally perfused subject) =
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Rate of coronary blood flow
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What is the effect of increased contractility, increased heart rate, increased systolic pressure/chamber volume on myocardial oxygen consumption?
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Increase rate of myocardial oxygen consumption and therefore the rate of coronary blood flow
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What occurs when coronary oxygen supply falls short of myocardial oxygen demand?
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Myocardial ischemia
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If heart rate is increased from 60 bpm to 120 bpm what is the effect on myocardial oxygen consumption and coronary blood flow?
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It will also double.
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If coronary flow is limited, what is the danger associated with interventions augmenting HR, BP or contractility?
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These interventions increase myocardial oxygen consumption and if flow is limited bring on or increase myocardial ischemia
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What is the most important influence in controlling coronary blood flow?
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Metabolic regulation
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List one metabolite known to cause coronary vasodilation.
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Adenosine
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Define: the blood pressure gradient driving flow from arteries to veins
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Perfusion pressure
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Describe how perfusion pressure is important in coronary circulation.
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Despite the presence of metabolites, if there is not adequate perfusion pressure there will not be blood flow
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During what phase of the cardiac cycle does blood flow to most of the ventricular wall occur?
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During diastole (during systole intramyocardial pressure collapses the vessels)
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What is the effect of an increase in left ventricular diastolic pressure on the subendocardial capillary beds?
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They are collapsed potentially resulting in mild heart ischemia
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Shear stress on the endothelial wall releases what vasodilator in coronary circulation (and probably systemic?)?
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Nitric Oxide
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What effect does prostacyclin have on coronary circulation?
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Vasodilation
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What effect does adrenergic (sympathetic) nerve terminals have on vascular smooth muscle?
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Tends to contract vascular smooth muscle resulting in constriction
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True/False: Minor and even moderate degrees of conduit blockage have no effect on coronary arteries.
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TRUE
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With increase in luminal blockage greater than ____ % maximum flow in the affected artery is progressively reduced.
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50 % results in progressive reduction in coronary artery flow
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Obstruction of at least ______% maximum flow interferes with coronary blood flow even at rest.
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90%
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Describe myocardial hibernation.
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Sustained reduction in perfusion by a sustained decrease in contractile and metabolic activity
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Normally is conduit resistance greater or smaller relative to microvessel resistance?
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Much smaller
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How is microvasscular resistance effect in coronary occlusive disease?
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Since the conduit resistance is increased (via coronary artery stenosis) the microvasculature shrinks to compoensate (resulting in loss of metabolic regulation)
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What is the effect of the shrinking of microvasculature in coronary occlusive disease on metabolic regulation?
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Metabolic regulation is lost
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What effect does the loss of metabolic regulation have on the heart?
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Makes the myocardium vulnerable to ischemia whenever blood pressure is low
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List three factors which exacerbate the hemodynamic effects of coronary stenosis.
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Markedly decreased arterial pressure, thrombosis, and coronary artery spasm
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List three factors which mitigate the hemodynamic effects of coronary stenosis.
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Thrombolysis, coronary collateral formation, and arterial wall remodeling
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Give a nonatherosclerotic cause of coronary occlusive disease.
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myocardial hypertrophy due to longstanding hypertension (resulting from outgrowing the blood supply)
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