Cardiac Performance, Dr. D. Penney


Alterations in contractile state: using systolic reserve volume (more complete emptying), through enhanced inotropicity.

Observed in:

  • exercise
  • digitalis treatment
  • catecholamine infusion

    Results in:

  • decreased EDV
  • decreased ESV
  • increased SV
  • increased stroke work
  • increased Ejection Fraction
  • increased ATP utilization, at lower efficiency

    Note: The diagram at right (and in Fig. 2.05) shows what happens in the first few cardiac cycles after contractility is abruptly increased. It reflects more accurately the real world than the previous two figures (A & B). Clearly, afterload and preload are altered, because they are all mechanically inter-related. Increased strength of contraction at first increases ventricular emptying, ie. increases stroke volume and ejection fraction. The point at which the aortic valve closes moves down the isovolumic pressure line. This increases blood volume in the aorta and the arterial tree, increasing afterload. This later tends to readjust upward, the point at which the aortic valve closes. Increased movement of blood to the arteries, empties the veins and decreases preload. This tends to move to the left the point at which the mitral valve closes.

    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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