Kirkpatrick S E, Naliboff J, Pitlick P T, Friedman W F
Am J Physiol. 1975 Aug;229(2):318-23. doi: 10.1152/ajplegacy.1975.229.2.318.
Isolated cardiac muscle techniques and studies of the chronically instrumented fetal lamb heart were employed to evaluate the ability of fetal myocardium to exhibit poststimulation potentiation. Isometric tension development and the response to paired electrical stimulation were significantly reduced in isolated fetal ventricular myocardium when compared to the adult (P less than 0.001). As in the adult, increasing stimulation frequency raised fetal isometric tension via an increase in the rate of rise of tension development in the presence of reduction in time-to-peak tension. In seven fetal lambs the left ventricle was chronically instrumented with endocardial ultrasonic crystals and a high-fidelity micromanometer. After a 2-wk recovery period, heart rate was increased by atrial pacing from an average control level of 150 to 300 beats/min. Left ventricular dP/dt increased progressively and then fell beyond a heart rate of 270/min. When comparable pre- and immediate postpacing beats were analyzed, a step-wise increase in the velocity of left ventricular shortening and the mean rate of circumferential fiber shortening was observed in association with an increase in the extent of shortening. Thus, increases in the frequency of contraction exert a significant positive inotropic effect on the fetal heart.
采用离体心肌技术和对长期植入仪器的胎羊心脏进行研究，以评估胎儿心肌表现出刺激后增强作用的能力。与成年心肌相比，离体胎儿心室心肌的等长张力发展和对成对电刺激的反应显著降低（P<0.001）。与成年心肌一样，在峰值张力时间缩短的情况下，增加刺激频率可通过增加张力发展的上升速率来提高胎儿等长张力。在7只胎羊中，左心室长期植入心内膜超声晶体和高保真微测压计。经过2周的恢复期后，通过心房起搏使心率从平均对照水平150次/分钟增加到300次/分钟。左心室dp/dt逐渐增加，然后在心率超过270次/分钟时下降。当分析可比的起搏前和起搏后即刻搏动时，观察到左心室缩短速度和圆周纤维缩短平均速率逐步增加，同时缩短程度也增加。因此，收缩频率的增加对胎儿心脏产生显著的正性肌力作用。
