Itskovitz J, Goetzman B W, Rudolph A M
Am J Obstet Gynecol. 1982 Jan 1;142(1):66-73. doi: 10.1016/s0002-9378(16)32286-4.
The responses of fetal heart rate and blood pressure to a transient reduction in uterine blood flow were studied in normoxemic and chronically hypoxemic lambs. In normoxemic fetuses, a reduction in uterine blood flow, if prolonged sufficiently, produced reflex bradycardia mediated through chemoreceptors and was associated with a decrease in carotid arterial PO2 to below 20 torr. The bradycardia was associated with a marked decrease in left ventricular output as measured by electromagnetic flowmeter; both were abolished by atropine. In chronically hypoxemic fetuses, a reduction in uterine blood flow produced a delayed deceleration of the heart rate which consisted of three components: reflex bradycardia due to chemoreceptor stimulation; baroreceptor-mediated reflex bradycardia which involved the slow and late recovery of the heart rate; and nonreflex bradycardia which was probably secondary to hypoxic myocardial depression. Quantitative analysis revealed a relationship between the components of delayed deceleration and the status of fetal oxygenation prior to the reduction in uterine blood flow. The lower the carotid arterial PO2, the shorter was the delay in the onset of bradycardia, the greater the decrease in heart rate, and the more prolonged the duration of bradycardia. The conclusion is that the response of fetal heart rate to a transient reduction in uterine blood flow is related to the duration of the reduction and to the status of fetal oxygenation prior to the decrease in uterine blood flow.
在血氧正常和慢性低氧血症的羔羊中，研究了胎儿心率和血压对子宫血流短暂减少的反应。在血氧正常的胎儿中，如果子宫血流减少持续足够长的时间，会产生通过化学感受器介导的反射性心动过缓，并伴有颈动脉血氧分压降至20托以下。心动过缓与电磁流量计测量的左心室输出量显著减少有关；两者都被阿托品消除。在慢性低氧血症的胎儿中，子宫血流减少会导致心率延迟减速，其由三个部分组成：化学感受器刺激引起的反射性心动过缓；压力感受器介导的反射性心动过缓，涉及心率的缓慢和延迟恢复；以及可能继发于缺氧性心肌抑制的非反射性心动过缓。定量分析揭示了延迟减速的各组成部分与子宫血流减少前胎儿氧合状态之间的关系。颈动脉血氧分压越低，心动过缓开始的延迟越短，心率下降越大，心动过缓持续的时间越长。结论是，胎儿心率对子宫血流短暂减少的反应与减少的持续时间以及子宫血流减少前胎儿的氧合状态有关。
