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Cardiac Oxygen Demand

  • The heart exerts significant energy to pressurize the blood entering the ventricles and accelerate it through the vasculature. A significant amount of oxygen is required to fuel these energy-costly processes. Cardiac Oxygen Demand is largely dependent on three basic variables, as discussed below. Some texts may attempt to explain how these variables modulate cardiac oxygen demand; however, in reality such relationships are likely highly complex and beyond the scope of this text.
Major Variables
  • Ventricular Wall Tension
    • Generation of ventricular wall tension during systole is the most energy-costly process of cardiac function. Consequently, the afterload against which the heart pumps is the dominant variable determining the quantity of myocardial oxygen consumption.
  • Heart Rate
    • Naturally, the rate of oxygen consumption by the heart is proportional to the frequency of heart pumping (i.e. the heart rate).
  • Contractility
    • Myocardial oxygen consumption also appears to be related to myocardial contractility. This is likely because processes which increase myocardial contractility also increase the quantity of ventricular wall tension generated by the myocardium.