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13 Cards in this Set
- Front
- Back
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What is contractility?
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The ability of the myocardium to develop a force at a given muscle length.
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What is another term for contractility?
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Inotropism
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What can be used as an estimate of contractility?
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Ejection fraction(EF)
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What is the expression for EF?
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EF= SV
___________ EDV X 100% |
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What is the normal range of EF?
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The normal range of EF is about 55-80%.
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What is a positive inotropic agent?
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Anything that causes an increase in contractility.
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What are some positive inotropes?
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Increased HR
Sympathetic stimulation Increased intracellular Ca+ Decreased extracellular Na+ Cardiac glycosides |
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What are some negative inotropes?
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Parasympathetic stimulation
beta 1 blockade Heart failure Acidosis Hypoxia Hypercapnia |
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How does sympathetic stimulation increase contractility?
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Increases inward Ca+ current during phase 2 and phopholamban is phosphorylated to increase the activity of the Ca+ pump of the SR providing more Ca+ for release.
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What receptor does the sympathetic nervous system use to increase contractility?
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Beta 1 receptors
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What is the neurotransmitter for the sympathetic nervous system effect?
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Catecholamines
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How does parasympathetic stimulation decrease contractility?
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Muscarinic receptors are stimulated by ACh to decrease the inward Ca+ current during phase 2.
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How do cardiac glycosides increase contractility?
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Myocardial cell membrane Na+-K+-ATPase is inhibited, which diminishes the Na+ gradient across the cell membrane. This decreased gradient causes the Na+-Ca+ exchange mechanism to increase intracellular Ca+.
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