RESUMO
In the human the heart contracts more than 2.0 billion times during the lifetime. The total amount of energy required in this period is equivalent to lift a huge tanker (more than 200 thousand tons) above your head. Thus there is no question that the heart requires a huge amount of energy. Since minimization of energy requirements would be one of the major design goals of the cardiovascular system, we investigated energy efficiency of ventriculo-arterial coupling under various conditions. In normal conscious dogs, the arterial system extracted maximal work from the left ventricle during exercise as well as at rest. At the same time, the energy consumption of the left ventricle to support the peripheral demand was minimum. This optimal coupling condition was well maintained despite changes in blood volume. The baroreflex system appeared to play a crucial role in this optimization. In the presence of left ventricular dysfunction, however, this optimality was no longer maintained. We conclude that the efficiency of cardiac contraction is fairly well maintained under various stresses as long as left ventricular function is normal.
