Department of Physiology, Monash University, Melbourne, Australia.
Respir Res. 2010 Aug 19;11(1):111. doi: 10.1186/1465-9921-11-111.
The onset of ventilation at birth decreases pulmonary vascular resistance (PVR) resulting in a large increase in pulmonary blood flow (PBF). As the large cross sectional area of the pulmonary vascular bed develops late in gestation, we have investigated whether the ventilation-induced increase in PBF is reduced in immature lungs.
Surgery was performed in fetal sheep at 105 d GA (n = 7; term ~147 d) to insert an endotracheal tube, which was connected to a neonatal ventilation circuit, and a transonic flow probe was placed around the left pulmonary artery. At 110 d GA, fetuses (n = 7) were ventilated in utero (IUV) for 12 hrs while continuous measurements of PBF were made, fetuses were allowed to develop in utero for a further 7 days following ventilation.
PBF changes were highly variable between animals, increasing from 12.2 ± 6.6 mL/min to a maximum of 78.1 ± 23.1 mL/min in four fetuses after 10 minutes of ventilation. In the remaining three fetuses, little change in PBF was measured in response to IUV. The increases in PBF measured in responding fetuses were not sustained throughout the ventilation period and by 2 hrs of IUV had returned to pre-IUV control values.
Ventilation of very immature fetal sheep in utero increased PBF in 57% of fetuses but this increase was not sustained for more than 2 hrs, despite continuing ventilation. Immature lungs can increase PBF during ventilation, however, the present studies show these changes are transient and highly variable.
出生时开始通气会降低肺血管阻力（PVR），从而导致肺血流量（PBF）大幅增加。由于肺血管床的大横截面积在妊娠晚期才发育，我们研究了通气引起的 PBF 增加是否在未成熟的肺中减少。
在妊娠 105 天的胎儿羊中进行手术（n = 7；足月约 147 天），插入气管内管，与新生儿通气回路连接，并在左肺动脉周围放置一个跨声速流量探头。在妊娠 110 天，胎儿（n = 7）在子宫内通气（IUV）12 小时，同时连续测量 PBF，通气后胎儿在子宫内再发育 7 天。
动物之间的 PBF 变化差异很大，4 只胎儿在通气 10 分钟后从 12.2 ± 6.6 毫升/分钟增加到最大值 78.1 ± 23.1 毫升/分钟。在其余 3 只胎儿中，IUV 后 PBF 几乎没有变化。在有反应的胎儿中测量到的 PBF 增加在通气期间并未持续，在 IUV 2 小时后已恢复到 IUV 前的对照值。
在子宫内对非常未成熟的胎儿羊进行通气会使 57%的胎儿的 PBF 增加，但尽管继续通气，这种增加也不会持续超过 2 小时。未成熟的肺可以在通气时增加 PBF，然而，目前的研究表明这些变化是短暂的，且变化很大。
