Abstract
Cardiac performance and myocardial energetics were studied during physical exercise in 19 subjects with congestive heart failure. Mechanical efficiency of the left ventricle was subnormal at rest and failed to rise normally during effort. The oxygen consumed by a unit weight of muscle at rest was not significantly different in the patients with failure than in the control subjects. With physical effort the oxygen consumption rose out of proportion to both the new work performed and the new pressure generated by the left ventricle. Changes in pressure-time/qO 2 ratio suggest that, unlike the normal ventricle, the failing ventricle is unable to effect a decrease in mean chamber volume during exercise and may actually become larger. No consistent evidence for myocardial hypoxia or anaerobiosis during stress was found. The low mechanical efficiency of the failing heart may be explained by (1) the large chamber volume (and tensile forces required); (2) organic failure or “after-load” inhibition of change in fiber shortening rate; and (3) further increase in heart size on effort. The fixed pressure-time per minute per oxygen consumption is probably related to an increase in heart size on effort and is a resultant of the above-mentioned factors.
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