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13 Cards in this Set

  • Front
  • Back
What is contractility?
The ability of the myocardium to develop a force at a given muscle length.
What is another term for contractility?
What can be used as an estimate of contractility?
Ejection fraction(EF)
What is the expression for EF?
EDV X 100%
What is the normal range of EF?
The normal range of EF is about 55-80%.
What is a positive inotropic agent?
Anything that causes an increase in contractility.
What are some positive inotropes?
Increased HR
Sympathetic stimulation
Increased intracellular Ca+
Decreased extracellular Na+
Cardiac glycosides
What are some negative inotropes?
Parasympathetic stimulation
beta 1 blockade
Heart failure
How does sympathetic stimulation increase contractility?
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.
What receptor does the sympathetic nervous system use to increase contractility?
Beta 1 receptors
What is the neurotransmitter for the sympathetic nervous system effect?
How does parasympathetic stimulation decrease contractility?
Muscarinic receptors are stimulated by ACh to decrease the inward Ca+ current during phase 2.
How do cardiac glycosides increase contractility?
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+.