The respiratory metabolism of the body depends on the supply of oxygen in the circulating blood. During its passage through active tissues the blood becomes depleted in respect to oxygen in proportion to the intensity of the metabolism, on the one hand, and the vigor of the circulation, on the other. The latter factor is maintained in large measure by the work of the blood pump, the heart. Accordingly, a recent writer1 has remarked that the efficiency of the heart is nothing else than the volume of blood that it can pump in relation to the oxygen requirement in the body. Otherwise defined, it is the ratio of the circulation, its volume per minute, to the oxygen requirement. On this basis the index of efficiency is therefore the arteriovenous oxygen difference during rest and various degrees of muscular exertion. This has become a measurable factor in man, the practical
EFFICIENCY OF THE HEART. JAMA. 1927;89(24):2042–2043. doi:10.1001/jama.1927.02690240034013
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