Fetal Physiology and Neuroscience Group and Circulatory Control Laboratory, Department of Physiology, University of Auckland, Auckland, New Zealand.
Exp Physiol. 2011 Aug;96(8):736-44. doi: 10.1113/expphysiol.2011.058354. Epub 2011 May 20.
Late preterm infants, born between 34 and 36 weeks gestation, have significantly higher morbidity than neonates born at full term, which may be partly related to reduced sensitivity of the arterial baroreflex. The present study assessed baroreflex control of heart rate (HR) and renal sympathetic nerve activity (RSNA) in near-term fetal sheep at 123 ± 1 days gestation. At this age, although fetuses are not fully mature in some respects (term is 147 days), sleep-state cycling is established [between high-voltage, low-frequency (HV) and low-voltage, high-frequency (LV) sleep], and neural myelination is similar to the term human infant. Fetal sheep were instrumented to record blood pressure (BP), HR (n = 15) and RSNA (n = 5). Blood pressure was manipulated using vasoactive drugs, phenylephrine and sodium nitroprusside. In both HV and LV sleep, phenylephrine was associated with increased arterial BP and decreased HR. In HV sleep, phenylephrine was associated with a fall in RSNA, from 124 ± 14 to 58 ± 11% (P < 0.05), but no significant change in RSNA in LV sleep. In contrast, the fall in BP after sodium nitroprusside was associated with a significant increase in HR during LV but not HV sleep, and there was no significant effect of hypotension on RSNA. These data demonstrate that in near-term fetal sheep baroreflex activity is only partly active and is highly modulated by sleep state. Critically, there was no RSNA response to marked hypotension; this finding has implications for the ability of the late preterm fetus to adapt to low BP.
晚期早产儿（妊娠 34 至 36 周之间出生）的发病率明显高于足月新生儿，这可能部分与动脉压力感受器反射的敏感性降低有关。本研究评估了 123±1 天妊娠的近足月胎儿的心率（HR）和肾交感神经活动（RSNA）的压力感受器反射控制。在这个年龄，尽管胎儿在某些方面尚未完全成熟（足月为 147 天），但睡眠状态已开始循环[高电压、低频率（HV）和低电压、高频率（LV）睡眠]，并且神经髓鞘形成与足月人类婴儿相似。对胎儿羊进行了仪器操作以记录血压（BP）、HR（n=15）和 RSNA（n=5）。通过血管活性药物（苯肾上腺素和硝普钠）来操纵血压。在 HV 和 LV 睡眠中，苯肾上腺素均与动脉血压升高和 HR 降低相关。在 HV 睡眠中，苯肾上腺素与 RSNA 降低相关，从 124±14%降至 58±11%（P<0.05），但在 LV 睡眠中 RSNA 无明显变化。相比之下，硝普钠引起的血压下降与 LV 睡眠而非 HV 睡眠时 HR 的显著增加相关，而低血压对 RSNA 没有明显影响。这些数据表明，在近足月胎儿中，压力感受器反射活动仅部分活跃，并受到睡眠状态的高度调节。至关重要的是，对于明显的低血压，没有 RSNA 反应；这一发现对晚期早产儿适应低血压的能力有影响。
