Burkhoff D, de Tombe P P, Hunter W C, Kass D A
Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205.
Am J Physiol. 1991 Feb;260(2 Pt 2):H569-78. doi: 10.1152/ajpheart.1991.260.2.H569.
Recent studies have shown that at the same endsystolic volume, ejecting beats can achieve a higher end-systolic pressure than isovolumic beats. The purpose of this study was to assess the metabolic cost, in terms of oxygen consumption (MVO2), and efficiency, in terms of the relation between MVO2 and pressure-volume area (PVA), of this increase in strength during ejection. The slope of the end-systolic pressure-volume relation (ESPVR) (Ees) was greater during ejecting than isovolumic contractions when ejection fraction (EF) was greater than approximately 30%, indicating an increase in contractile strength. The difference in Ees between the two modes of contraction was as much as 30% at EFs of 60%. In contrast, the slope of the MVO2-PVA relation was less during ejecting than isovolumic contractions, indicating a decrease in MVO2 at any given PVA. The difference in slope was as much as 20% at EFs of 60%. Thus afterload conditions, allowing substantial fiber shortening, shift the ESPVR toward greater contractile strength and increase the metabolic efficiency when viewed in terms of the relation between MVO2 and total mechanical energy generation (PVA) by the ventricle. This may reflect an energetically favorable effect of shortening on muscle force-generating capability.
最近的研究表明，在相同的收缩末期容积下，射血搏动比等容搏动能达到更高的收缩末期压力。本研究的目的是评估射血过程中这种力量增加所带来的代谢成本（以耗氧量，即MVO2衡量）以及效率（以MVO2与压力-容积面积，即PVA之间的关系衡量）。当射血分数（EF）大于约30%时，射血时收缩末期压力-容积关系（ESPVR）（Ees）的斜率比等容收缩时更大，表明收缩力增加。在EF为60%时，两种收缩模式下Ees的差异高达30%。相反，射血时MVO2-PVA关系的斜率比等容收缩时更小，表明在任何给定的PVA下MVO2都降低。在EF为60%时，斜率差异高达20%。因此，允许大量纤维缩短的后负荷条件会使ESPVR向更大的收缩力方向移动，并从MVO2与心室产生的总机械能（PVA）之间的关系来看提高代谢效率。这可能反映了缩短对肌肉力量产生能力的能量有利影响。
