Block B S, Schlafer D H, Wentworth R A, Kreitzer L A, Nathanielsz P W
Department of Obstetrics and Gynecology, University of Chicago.
Am J Obstet Gynecol. 1990 May;162(5):1325-31. doi: 10.1016/0002-9378(90)90046-a.
In response to acute hypoxemia, the fetus invokes physiologic compensatory mechanisms that cause a preferential redistribution of the circulation to sustain the brain, heart, and adrenal gland and maintain blood flow to the placenta. These mechanisms are available for a limited time and eventually the fetus is no longer able to maintain preferential perfusion and decompensation occurs. To identify the relationship between hypoxemia with severe acidemia and the breakdown of circulatory compensation, we decreased uterine blood flow in 10 chronically instrumented pregnant sheep. We measured fetal blood gases and pH, arterial and central venous pressures, heart rate, combined ventricular output, and regional blood flow distribution during hypoxemia with severe acidemia and when a fixed-baseline sustained bradycardia (agonal) heart rate pattern developed. Hypoxemia with severe acidemia was characterized by markedly decreased blood flow to most organs; however, the preferential perfusion of the brain, heart, adrenal gland, and placenta was still present. An agonal heart rate pattern was characterized by complete cardiovascular collapse. This study demonstrates that circulatory compensation is present in fetal sheep affected by deficiency of oxygen delivery despite hypoxemia with severe acidemia.
为应对急性低氧血症，胎儿会启动生理代偿机制，导致循环系统优先重新分配，以维持大脑、心脏和肾上腺的功能，并保持胎盘的血流。这些机制的作用时间有限，最终胎儿将无法维持优先灌注，进而发生失代偿。为确定严重酸血症性低氧血症与循环代偿功能衰竭之间的关系，我们减少了10只长期植入仪器的怀孕绵羊的子宫血流量。我们在严重酸血症性低氧血症期间以及出现固定基线持续性心动过缓（濒死）心率模式时，测量了胎儿的血气和pH值、动脉压和中心静脉压、心率、联合心室输出量以及局部血流分布。严重酸血症性低氧血症的特征是大多数器官的血流量显著减少；然而，大脑、心脏、肾上腺和胎盘仍存在优先灌注。濒死心率模式的特征是心血管系统完全崩溃。这项研究表明，尽管存在严重酸血症性低氧血症，但受氧输送不足影响的胎羊仍存在循环代偿。
