Circulating catecholamines are critical for fetal adaptation to hypoxia by regulating fetal heart rate (FHR) and promoting myocardial contractility and peripheral vasoconstriction. They have been hypothesized to contribute to changes in FHR variability (FHRV) and T wave morphology, clinical indices of fetal wellbeing during labor. β-adrenergic blockade with propranolol does not affect FHRV during labor-like hypoxemia and only attenuated the increase in T wave height between the episodes of hypoxemia. To further investigate the potential role of catecholamines, we investigated whether pharmacologic β-adrenergic stimulation could increase FHRV and T wave elevation during intermittent labor-like hypoxemia. 19 chronically instrumented fetal sheep at 0.85 of gestation received isoprenaline hydrochloride (n=7) or saline (control, n=12), followed by three 1-min complete umbilical cord occlusions (UCOs) separated by 4-min reperfusion periods. Before the UCOs, infusion of isoprenaline increased FHR (p<0.001), absolute-T/QRS ratio (p<0.001) and one measure of FHRV (root mean square of successive RR interval differences, RMSSD, p<0.05). UCOs triggered deep FHR decelerations. During UCOs, isoprenaline was associated with increased FHR (p<0.001) and absolute-T/QRS ratio (p<0.05), but no effect on T/QRS ratio was observed when normalized to baseline before UCOs (normalized-T/QRS ratio). Between UCOs, isoprenaline increased FHR (p<0.001) and absolute-T/QRS ratio (p<0.05) but did not affect normalized-T/QRS ratio or any measures of FHRV. Arterial pressure was not affected by isoprenaline at any point. Our findings indicate that circulating catecholamines regulate FHR but not FHRV during labor-like hypoxemia and promote T wave elevation between but not during intermittent fetal hypoxemia.

中文翻译：

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β-肾上腺素刺激对胎羊短暂脐带闭塞期间胎心率，心率变异性和T波升高的影响。

循环儿茶酚胺通过调节胎儿心率（FHR）并促进心肌收缩力和外周血管收缩，对于胎儿适应缺氧至关重要。据推测，它们可促进FHR变异性（FHRV）和T波形态，分娩时胎儿健康的临床指标的变化。普萘洛尔对β-肾上腺素的阻断在分娩样低氧血症期间不会影响FHRV，而只会减弱低氧血症发作之间T波高度的增加。为了进一步研究儿茶酚胺的潜在作用，我们研究了药理性β-肾上腺素能刺激是否可在间歇性劳动样低氧血症期间增加FHRV和T波升高。妊娠0.85的19头经长期仪器检查的胎羊接受盐酸异丙肾上腺素（n = 7）或生理盐水（对照组，n = 12），然后进行3次1分钟的完全脐带闭塞（UCO），再进行4分钟的再灌注。在UCO之前，输注异丙肾上腺素会增加FHR（p <0.001），绝对T / QRS比（p <0.001）和一种FHRV量度（连续RR间隔差的均方根，RMSSD，p <0.05）。UCO触发了深层FHR减速。在UCOs期间，异丙肾上腺素与FHR升高（p <0.001）和绝对T / QRS比（p <0.05）相关，但在UCOs归一化至基线之前未观察到对T / QRS比的影响（归一化T / QRS比）。在UCO之间，异丙肾上腺素增加FHR（p <0.001）和绝对T / QRS比（p <0.05），但不影响归一化T / QRS比或任何FHRV指标。异丙肾上腺素在任何时候都不会影响动脉压。