Chemical Energy Required for Cardiac
Contraction: Oxygen Utilization by the Heart
Heart muscle, like skeletal muscle, uses chemical energy to provide
the work of contraction. This energy is derived mainly from oxidative
metabolism of fatty acids and, to a lesser extent, of other nutrients,
especially lactate and glucose. Therefore, the rate of oxygen con-sumption by
the heart is an excellent measure of the chemical energy liberated while the
heart performs its work.
Efficiency of Cardiac Contraction. During heart muscle
con-traction, most of the expended chemical energy is con-verted into heat and a much smaller portion into workoutput. The ratio of work output to
total chemicalenergy expenditure is called the efficiency of cardiaccontraction, or simply efficiency of the heart. Maximumefficiency of the normal heart is
between 20 and 25 per cent. In heart failure, this can decrease to as low as 5
to 10 per cent.
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