Previous Beat Ejection but Not Previous Beat Pressure Load

Previous beat contraction history, in which the performance of the left ventricle on any one beat is influenced by the mechanical events of the previous beat, may be important in the beat-to-beat regulation of left ventricular performance in the intact cardiovascular system. Prior studies of this phenomenon have established that mechanical events of the previous beat influence the function of the current beat, but it is not known whether the important mechanical influence is exerted by previous beat ejection or previous beat pressure. In addition, the magnitude of the effect of previous beat contraction history on left ventricular performance is unknown. To make these determinations, we performed experiments in six isolated rabbit left ventricle preparations buffer perfused at 30°C. Left ventricular pressure and volume were controlled precisely with a servo-controlled linear motor system. After steady-state ejecting conditions were established by clamping left ventricular ejection pressure at 609% of peak isovolumic pressure, single test beats, which were pressure clamped at 40%o, 60%o, 80%, and 100l% of peak isovolumic pressure, were introduced and followed by an isovolumic reference beat. As the level of pressure clamp decreased from 100%/ to 40%o, developed pressure on the isovolumic beat following the single test beats increased from 139± 15 (mean± SD) to 151± 13