Abstract
The influence of an increase in the volume of the left ventricular chamber on myocardial oxygen consumption was studied in the heart-lung preparation modified to measure coronary flow. Left ventricular volume was increased by injecting saline into a rubber balloon stabilized in the left ventricular chamber away from the inflow and outflow tracts. At constant mean aortic pressure and cardiac output, left ventricular balloon volumes of 5, 10, 15, and 20 ml. increased minimal left ventricular end-diastolic volumes (balloon volume + stroke output) to 15·1 ± 0·6 ml. (52% above control values), 20·1 ± 0·7 ml. (104% above control values), 25·3 ± 0·7 ml. (157% above control values), and 29·5 ± 0·8 ml. (216% above control values), respectively. At these end-diastolic volumes, tension per cm2 of cross-sectional area of left ventricular muscle at the equator, increased above control values by 35%, 57%, 108%, and 147%, respectively. This was accompanied by an increase in oxygen consumption above control values averaging 4%, 16%, 39%, and 59%, respectively; the latter three values were statistically significant.
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