Anderson P A, Manring A, Crenshaw C
Am J Obstet Gynecol. 1980 Sep 1;138(1):33-43. doi: 10.1016/0002-9378(80)90008-3.
The force-interval relationship was evaluated in the developing heart of the lamb. The qualitative characteristics of the relationship were the same in isolated muscle (from 93 to 141 days' gestation to 1 year old) as in the chronically instrumented in utero fetus (122 to 141 days' gestation): (1) contractility, e.g., the maximum rate of rise of force, increased monotonically from a small value immediately after a contraction to a plateau, and (2) postextrasystolic potentiation was present in all preparations. In the intact animal, postextrasystolic potentiation depended on the basic pacing interval, t0, and the timing of the extrasystole, t1: when t0 was held constant and t1 was increased, potentiation decreased; when t1 was held constant and t0 was increased, potentiation increased. The qualitative characteristics of the relationship, and so the underlying myocardial basis, were unchanged over the developmental period studied.
在发育中的羔羊心脏中评估了力-间期关系。该关系的定性特征在离体肌肉（妊娠93至141天至1岁）中与慢性植入子宫内胎儿（妊娠122至141天）中相同：(1)收缩性，例如力的最大上升速率，从收缩后立即的小值单调增加至平台期，以及(2)所有标本中均存在期外收缩后增强。在完整动物中，期外收缩后增强取决于基本起搏间期t0和期外收缩的时间t1：当t0保持不变而t1增加时，增强作用减弱；当t1保持不变而t0增加时，增强作用增强。在所研究的发育阶段，该关系的定性特征以及潜在的心肌基础均未改变。
