MECHANICAL DETERMINANTS OF MYOCARDIAL OXYGEN-CONSUMPTION

1. Recent developments which attempt to identify the mechanical determ inants of myocardial oxygen consumption (mV(O2)) are considered, with emphasis being placed on the pressure-work and pressure-volume area (P VA) indices. 2. The difficulty of establishing a realistic in vivo bas al mV(O2) value is explained and the experimental reasons far the cont roversy over the magnitude of the activation metabolism are outlined. 3. The time varying elastance model of the heart is discussed includin g some current problems, The evidence for PVA as a satisfactory index of mV(O2) under all physiological and pharmacological conditions is ex amined, Most pharmacological agents alter the intercept of the mV(O2): PVA relationship but do not effect its slope: this result is interpret ed to mean that the majority of current inotropic agents alter the ene rgetic cost of calcium release/retrieval but not crossbridge efficienc y, 4. An attempt is made to establish the likely cost of a cardiac con traction in man, The use of newer technology (i) to estimate mV(O2) vi a positron emission tomography and (ii) to measure the work and potent ial energy output of the heart per beat with conductance catheters, is explained.