Heart Research, Murdoch Children's Research Institute , Parkville, Victoria , Australia.
Department of Paediatrics, University of Melbourne , Melbourne , Australia.
Am J Physiol Regul Integr Comp Physiol. 2019 Jun 1;316(6):R716-R724. doi: 10.1152/ajpregu.00318.2018. Epub 2019 Mar 6.
The glucocorticosteroid betamethasone is routinely administered via maternal intramuscular injection to enhance fetal lung maturation before anticipated preterm birth. Although antenatal betamethasone increases fetal pulmonary arterial (PA) blood flow, whether this agent alters the contribution of ) right ventricular (RV) output or ) left-to-right shunting across the ductus arteriosus to rises in PA blood flow after preterm birth is unknown. To address this question, anesthetized control ( = 7) and betamethasone-treated ( = 7) preterm fetal lambs (gestation 127 ± 1 days, means ± SD) were instrumented with aortic, pulmonary, and left atrial catheters as well as ductus arteriosus and left PA flow probes to calculate RV output, with hemodynamics measured for 30 min after cord clamping and mechanical ventilation. Mean PA blood flow was higher in betamethasone-treated than in control lambs over the initial 10 min after birth ( < 0.05). This higher PA flow was accompanied by a greater pulmonary vascular conductance ( ≤ 0.025), a larger proportion of RV output passing to lungs ( ≤ 0.01), despite a fall in this output, and earlier reversal and a greater magnitude ( ≤ 0.025) of net ductal shunting, due to the combination of higher left-to-right ( ≤ 0.025) and lesser right-to-left phasic shunting ( ≤ 0.025). These results suggest that antenatal betamethasone augments the initial rise in PA blood flow after birth in preterm lambs, with this augmented rise supported by the combination of ) a greater redistribution of RV output toward the lungs and ) a faster and larger reversal in net ductal shunting underpinned not only by greater left-to-right, but also by lesser right-to-left phasic shunting.
倍他米松是一种糖皮质激素，通常通过肌内注射给予孕妇，以在预计早产前增强胎儿肺成熟度。尽管产前倍他米松增加胎儿肺动脉 (PA) 血流，但这种药物是否改变右心室 (RV) 输出的贡献或动脉导管内的左向右分流对早产后 PA 血流升高的影响尚不清楚。为了解决这个问题，麻醉对照组（n = 7）和倍他米松治疗组（n = 7）的早产羔羊（妊娠 127 ± 1 天，平均值 ± 标准差）接受了主动脉、肺动脉和左心房导管以及动脉导管和左肺动脉流量探头的置管，以计算 RV 输出，在脐带夹闭和机械通气后 30 分钟测量血流动力学。出生后最初 10 分钟，倍他米松治疗组的平均 PA 血流高于对照组（<0.05）。这种较高的 PA 流量伴随着较高的肺血管传导率（≤0.025）和较大的 RV 输出流向肺部的比例（≤0.01），尽管 RV 输出下降，以及更早的逆转和更大的净导管分流幅度（≤0.025），这是由于较高的左向右分流（≤0.025）和较少的右向左相分流（≤0.025）的组合。这些结果表明，产前倍他米松增强了早产羔羊出生后 PA 血流的初始升高，这种增强的升高是由 RV 输出向肺部的更大再分布和净导管分流的更快和更大逆转共同支持的，这不仅取决于更大的左向右分流，还取决于较小的右向左相分流。
