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Myocardial O2 consumption: determinants

The amount of oxygen consumed is determined by the basal O2 consumption, wall tension, contractility and heart rate.

Wall tension =(pressure*radius)/2*wall thickness

pressure = afterload; radius = preload

Pressure alone is not a good measure for myocardialO2consumption unless the other factors above are considered.

The greater the contractility, the more oxygen the myocardium consumes. Faster, more powerful contractions (increased dP/dT) requires more energy.

Increased HR leads to increased myocardialO2consumption. Heart rate is extremely important in that it influences not only supply, but demand as well, as the myocardium is perfused during diastole.

In the unanesthetized individual, myocardial consumption is the main determinant of myocardial supply.