Cardiac Performance, Dr. D. Penney

Major factors determining myocardial contractile state (ie. inotropicity)

  • Sympathetic nerve impulses (normal)

  • Circulating catecholamines (normal)

  • Force-frequency relation (Bowditch, Treppe, Staircase) Normal)

  • Various natural inotropic agents (normal)

  • Digitalis, other non-natural inotropic agents (medical)

  • Anoxia, hypercapnia, acidosis (pathologic)

  • Pharmacologic depressants (medical / pathologic)

  • Loss of myocardium (pathologic)

  • Intrinsic depressants (normal / pathologic)

    Attention: Inotropicity (ie. contractility) and strength of contraction are not synonomous. Increased / decreased strength of contraction can be achieved by changing preload
    (ie. Frank-Starling) with no change in inotropicity. Inotropicity reflects the biochemical state within the muscle (eg. Ca, ATP), not simply the positioning of the thick and thin
    myofilaments as determined by stretch.

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