Derived Indices of Myocardial Function in Isolated Work-Performing Hearts
Quantitative measurements of the status of myocardial function and of changes in function produced by experimental conditions or agents are difficult to obtain. The difficulties increase when heart-to-heart comparisons are required. Clinically, the introduction and improvement of cardiac catheterization, electro- and echocardiography, and real-time radioopaque and radionuclide imaging have lessened the difficulty of this task somewhat. In animal experiments, greater quantitation has been attempted by direct measurements of pressures and their rates of change in most vessels and cavities of the heart and the circulatory system. Strain gauge arches and ultrasonic dimension crystals have been used to quantitate isometric force development (F), including rate change (dF/dt), and to accurately and directly determine wall thickness changes and diameter changes of heart chambers. In addition, information about isotonic contraction, velocity of contractile element shortening, velocity of circumferential fiber shortening, and maximum velocity of shortening can be obtained. Accurate and convenient flow and combined flow (cardiac output) measurements are possible. This information allows reliable calculation of preload and afterload, ventricular volumes and their changes, atrial and ventricular end-diastolic pressures, cardiac output, and stroke volume for a meaningful construction of Starling function curves.
KeywordsCardiac Output Coronary Flow Venous Return Myocardial Function Pressure Load
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