Myocardial Oxygen Consumption During Ventricular Contraction and Relaxation

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Abstract
Determinations of left ventricular oxygen consumption were made in the isolated heart of a dog while the ventricle performed work by compressing air. In the described preparation the air compressed by the ventricle could be rapidly released and the ventricular pressure pulse repeatedly interrupted at specific points during its cycle. Upon interrupting the pressure pulse at its peak there was a 10% increase in peak pressure that appeared in the subsequent four to five beats. When the intraventricular pressure was released at various points during its ascent to peak pressure, left ventricular oxygen consumption could be correlated with both the pressure, at which it was interrupted, and the area under the pressure pulse. When the oxygen consumed by a ventricle developing a full pressure pulse was compared to that of a ventricle in which the intraventricular pressure was released at its peak-land when the peak systolic pressure of the two compared pulses were equal-then the oxygen consumed by the ventricle when the pulse was interrupted averaged 91% of that when the pulse was full. These studies indicate that by the time the pressure pulse has reached its peak, myocardial oxygen consumption has been largely determined, and that the oxygen cost of the ventricular relaxation is small.