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Ischemia in isolated interventricular septa: mechanical events

K I Shine, A M Douglas, N Ricchiuti

    The American Journal of Physiology
    |October 1, 1976
    PubMed
    Summary

    Global ischemia impairs heart muscle function, with recovery rates varying by temperature and ion concentration. Potassium supplementation enhances mechanical recovery after ischemia in rabbit septa.

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    Area of Science:

    • Cardiovascular Physiology
    • Ischemic Heart Disease Research
    • Myocardial Function Studies

    Background:

    • Global ischemia significantly impacts myocardial mechanical function.
    • Understanding the kinetics of ischemia and reperfusion is crucial for developing therapeutic strategies.
    • Rabbit interventricular septa provide a model for studying global ischemia.

    Purpose of the Study:

    • To investigate the effects of global ischemia on myocardial mechanical function in isolated blood-perfused rabbit septa.
    • To determine the influence of temperature and ion concentrations (calcium, potassium) on the decline and recovery of cardiac function during ischemia and reperfusion.
    • To elucidate the rate-limiting steps in myocardial ischemia and reperfusion.

    Main Methods:

    • Isolated blood-perfused rabbit interventricular septa were subjected to global ischemia in a nitrogen atmosphere.
    • Developed tension (DT), maximal rate of tension development (+dP/dt), and maximal rate of relaxation (-dP/dt) were measured.
    • Experiments were conducted at varying temperatures (37°C, 28°C) and with different calcium (5 mM) and potassium (10 mM) concentrations.
    • Time-to-peak tension (TPT) and action potential duration were also monitored.

    Main Results:

    • During ischemia, DT and -dP/dt declined monoexponentially (λ = 0.39 min⁻¹ at 37°C).
    • +dP/dt declined similarly to DT after a 60-90s delay; TPT shortened immediately, while action potential duration shortened later.
    • Calcium (5 mM) slowed the decline of +dP/dt (λ = 0.26 min⁻¹).
    • Reperfusion after 10 min of ischemia showed similar recovery rates (λ = 0.21–0.23 min⁻¹) independent of temperature, but recovery magnitude was reduced at 37°C.
    • Potassium (10 mM) did not affect decline rates but significantly increased recovery magnitude (P < 0.01).

    Conclusions:

    • Myocardial mechanical function declines during global ischemia, with distinct kinetics for different parameters.
    • Recovery of mechanical function upon reperfusion is temperature-independent in rate but sensitive in magnitude.
    • Potassium supplementation enhances the magnitude of mechanical recovery post-ischemia.
    • Results suggest that depletion and/or repletion of single cellular compartments are rate-limiting steps in ischemia and reperfusion.

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