Neonatal Intensive Care Unit, Máxima Medical Centre, Veldhoven, The Netherlands.
Pediatr Res. 2013 Apr;73(4 Pt 1):420-6. doi: 10.1038/pr.2013.15. Epub 2013 Jan 22.
The understanding of hypoxemia-induced changes in baroreflex function is limited and may be studied in a fetal sheep experiment before, during, and after standardized hypoxic conditions.
Preterm fetal lambs were instrumented at 102 d gestation (term: 146 d). At 106 d, intrauterine hypoxia--ischemia was induced by 25 min of umbilical cord occlusion (UCO). Baroreflex-related fluctuations were calculated at 30-min intervals during the first week after UCO by transfer function (cross-spectral) analysis between systolic blood pressure (SBP) and R-R interval fluctuations, estimated in the low-frequency (LF, 0.04-0.15 Hz) band. LF transfer gain (baroreflex sensitivity) and delay (s) reflect the baroreflex function.
Baseline did not differ in LF transfer gain and delay between controls and the UCO group. In controls, LF gain showed postnatal increase. By contrast, LF gain gradually decreased in the UCO group, resulting in significantly lower values 4-7 d after UCO. In the UCO group, LF delay increased and differed significantly from controls.
Our results show that intrauterine hypoxia-ischemia results in reduced baroreflex sensitivity over a period of 7 d, indicating limited efficacy to buffer BP changes by adapting heart rate. Cardiovascular dysregulation may augment already present cerebral damage after systemic hypoxia-ischemia in the reperfusion period.
对低氧血症引起的压力反射功能变化的理解有限，并且可以在胎儿羊实验中进行研究，该实验在标准化低氧条件之前、期间和之后进行。
在妊娠 102 天时对早产羔羊进行仪器操作（足月：146 天）。在 106 天，通过脐带结扎（UCO）25 分钟来诱导宫内缺氧-缺血。在 UCO 后的第一周内，通过在低频（LF，0.04-0.15 Hz）频段之间计算收缩压（SBP）和 R-R 间隔波动之间的传递函数（交叉谱）分析，来计算与压力反射相关的波动，LF 传递增益（压力反射敏感性）和延迟（s）反映了压力反射功能。
在 LF 传递增益和延迟方面，对照组和 UCO 组之间的基线没有差异。在对照组中，LF 增益显示出产后增加。相比之下，LF 增益在 UCO 组中逐渐降低，导致 UCO 后 4-7 天的数值显著降低。在 UCO 组中，LF 延迟增加，与对照组有显著差异。
我们的结果表明，宫内缺氧-缺血导致压力反射敏感性在 7 天内降低，表明通过适应心率来缓冲血压变化的效果有限。心血管失调可能会在再灌注期全身性缺氧-缺血后增加已经存在的脑损伤。
