Anderson P A, Manring A, Crenshaw C
Am J Obstet Gynecol. 1980 Sep 1;138(1):44-54.
The interaction of the force-interval relationship, muscle length (ventricular volume), and inotropy was evaluated in isolated fetal myocardial preparations and in the in utero chronically instrumented fetal lamb. In the isolated muscle, 93 to 141 days' gestation, a change in muscle length strengthened all contractions equally (multiplicatively) but produced no other changes in either the quantitative or the qualitative characteristics of the force-interval relationship; it was significantly altered by isoproterenol. Similarly, in the intact fetal lamb the qualitative and quantitative features of the relationship did not depend on ventricular volume, e.g., postextrasystolic potentiation was constant over a wide range of volumes. But isoproterenol produced a decrease in postextrasystolic potentiation. These results demonstrate that the force-interval relationship satisfies two major criteria for an index of cardiac contractility and suggest that the relationship may provide a basis for the evaluation of changes in contractility with development and birth.
在离体胎儿心肌标本以及子宫内长期植入仪器的胎羊身上，对力-间期关系、肌肉长度（心室容积）和心肌收缩力之间的相互作用进行了评估。在妊娠93至141天的离体肌肉中，肌肉长度的变化会同等程度地（成倍地）增强所有收缩，但在力-间期关系的定量或定性特征方面不会产生其他变化；异丙肾上腺素会使其发生显著改变。同样，在完整的胎羊中，该关系的定性和定量特征并不取决于心室容积，例如，早搏后增强在很宽的容积范围内是恒定的。但异丙肾上腺素会导致早搏后增强减弱。这些结果表明，力-间期关系满足作为心脏收缩性指标的两个主要标准，并提示该关系可能为评估发育和出生过程中收缩性的变化提供基础。
