Ventricular Matching with the Arterial System in Chronically Instrumented Dogs
We investigated how exercise (physiologic stress) and cardiac dysfunction (pathologic stress) influence the mechanical energy transmission from the left ventricle to the arterial system. With exercise, end-systolic elastance (Ees) increased by 46% and effective arterial elastance (Ea) increased by 35%, while the ratio of Ea to Ees remained fairly constant. The estimated ratio (Qmch) of external work to its theoretically derived maximal value was 0.95 ± 0.06 at rest and 0.93 ± 0.10 during maximal exercise. Similarly the ratio (Qmtb) of estimated minimum oxygen consumption of the heart to that actually measured to achieve a given level of cardiac output and arterial pressure was 0.97 ± 0.02 at rest and 0.98 ± 0.02 during exercise. With the creation of left ventricular dysfunction, Qmch was still close to unity (0.94 ± 0.07) in spite of a significant increase in Ea/Ees (1.42 ± 0.58). Qmtb, on the other hand, was significantly lowered (0.81 ± 0.09). We conclude that external work of the left ventricle of normal dogs is at a near-maximal level during exercise as well as at rest without compromising metabolic efficiency. In the left ventricle with dysfunction, external work is still close to optimal, whereas metabolic efficiency has significantly deteriorated.
KeywordsLeft Ventricle Left Ventricular Dysfunction External Work Ventricular Contractility Mechanical Optimality
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