Smolich Joseph J
Heart Research, Murdoch Children's Research Institute, Parkville, Victoria, Australia.
Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia.
J Physiol. 2025 Jul 31. doi: 10.1113/JP288749.
A widely held view is that an increased pulmonary arterial (PA) blood flow at birth is not triggered until the onset of lung aeration, but experimental data indicate that the non-ventilatory events of a reduction in lung liquid volume, complete fetal delivery, and umbilical cord clamping can also increase fetal PA flow. However, the effect of cord clamping strategy on the contribution of these non-ventilatory events to birth-related rises in PA flow is unknown. Accordingly, PA blood flow was measured via transit-time flow probe in anaesthetized, acutely instrumented preterm fetal lambs at baseline, after a ∼35% reduction in lung liquid volume, following complete fetal delivery, and then after (1) delayed cord clamping (DCC) preceded by ventilation lasting ∼100 s (n = 11), or (2) early cord clamping (ECC) followed by either a non-asphyxial (∼35 s, n = 10) or an asphyxial interval (∼100 s, < 10 mmHg, n = 10) before ventilation. PA flow rose stepwise after reduction of lung liquid volume (P < 0.001) and fetal delivery (P < 0.001), as well as initial ventilation (P < 0.001) and subsequent DCC (P = 0.002). PA flow also rose after ECC (P < 0.001), with flow maintained in the non-asphyxial group, but markedly reduced to near-baseline fetal levels by pulmonary vasoconstriction in the asphyxial group (P = 0.009), before rising with ventilation (P < 0.001). Overall, non-ventilatory events cumulatively accounted for ∼30% of the fetal baseline-to-peak newborn increment in PA flow. These findings suggest that (1) non-ventilatory events substantially contribute to a perinatal rise in PA blood flow with ECC or DCC, and (2) this contribution is negated if an asphyxial level of arterial oxygenation develops after ECC. KEY POINTS: Although a widely held view is that an increased pulmonary blood flow (PBF) at birth is not triggered until onset of lung aeration, reduction of lung liquid volume, complete fetal delivery and umbilical cord clamping also increase fetal PBF. The contribution of these non-ventilatory events to birth-related rises in PBF is unknown, particularly with different cord clamping strategies. Anaesthetized preterm fetal lambs instrumented with central arterial flow probes underwent birth via delayed cord clamping (DCC) preceded by ventilation, or early cord clamping (ECC) followed by either a non-asphyxial or asphyxial interval before ventilation. PBF rose with reduction of lung liquid volume, fetal delivery, ECC and DCC. However, while an increased PBF after ECC was maintained with a non-asphyxial interval, it fell markedly after ECC with an asphyxial interval, before rebounding with ventilation. Cumulatively, non-ventilatory events accounted for ∼ 30% of the perinatal increase in PBF occurring with DCC or ECC birth strategies.
一种广泛持有的观点是，出生时肺动脉（PA）血流增加直到肺通气开始才会触发，但实验数据表明，肺液体积减少、胎儿完全娩出和脐带钳夹等非通气事件也会增加胎儿PA血流。然而，脐带钳夹策略对这些非通气事件在与出生相关PA血流升高中所起作用的影响尚不清楚。因此，在麻醉状态下，通过经时血流探头对急性植入仪器的早产胎儿羔羊进行测量，在基线时、肺液体积减少约35%后、胎儿完全娩出后，然后在（1）持续约100秒通气后延迟脐带钳夹（DCC）（n = 11），或（2）早期脐带钳夹（ECC）后，在通气前先有一个非窒息期（约35秒，n = 10）或窒息期（约100秒，动脉血氧分压<10 mmHg）（n = 10）。肺液体积减少后（P < 0.001）、胎儿娩出后（P < 0.001）、初始通气时（P < 0.001）以及随后的DCC时（P = 0.002），PA血流呈逐步上升。ECC后PA血流也上升（P < 0.001），在非窒息组血流得以维持，但在窒息组中，在通气前因肺血管收缩PA血流显著降至接近胎儿基线水平（P = 0.009），随后通气时血流上升（P < 0.001）。总体而言，非通气事件累计占胎儿基线至新生儿峰值PA血流增量的约30%。这些发现表明：（1）非通气事件在ECC或DCC时对围产期PA血流升高有显著贡献；（2）如果ECC后出现动脉氧合的窒息水平，这种贡献会被抵消。要点：尽管一种广泛持有的观点是出生时肺血流增加直到肺通气开始才会触发，但肺液体积减少、胎儿完全娩出和脐带钳夹也会增加胎儿肺血流。这些非通气事件在与出生相关肺血流升高中的作用尚不清楚，特别是在不同的脐带钳夹策略下。用中心动脉血流探头植入的麻醉早产胎儿羔羊通过通气后延迟脐带钳夹（DCC）或早期脐带钳夹（ECC）并在通气前先有一个非窒息期或窒息期来模拟出生过程。肺液体积减少、胎儿娩出、ECC和DCC时肺血流均上升。然而，虽然ECC后非窒息期肺血流增加得以维持，但ECC后窒息期肺血流显著下降，然后在通气时反弹。总体而言，非通气事件在DCC或ECC出生策略导致的围产期肺血流增加中占约30%。
