Ong Tracey, Sobotka Kristina S, Siew Melissa L, Crossley Kelly J, van Vonderen Jeroen J, Polglase Graeme R, Hooper Stuart B
The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Victoria, Australia.
Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia.
Arch Dis Child Fetal Neonatal Ed. 2016 Nov;101(6):F540-F545. doi: 10.1136/archdischild-2015-309596. Epub 2016 Apr 8.
A sustained bradycardia is used as a major indicator of severe perinatal asphyxia. However, lambs asphyxiated ex utero do not exhibit the same bradycardic response as lambs asphyxiated in utero. It is possible that the local in utero environment may influence the initial cardiovascular response to asphyxia. We assessed the effect of facial immersion in water on the cardiovascular response to birth asphyxia.
Pregnant ewes (138±1 days gestation) were anaesthetised and fetuses were exteriorised and instrumented for measurement of cardiopulmonary haemodynamics. The lamb's head either remained in air (n=5) or was placed in water that was either warm (40±1°C; n=5) or at room temperature (21±1°C; n=5) before the umbilical cord was clamped to induce asphyxia.
Heart rate after bradycardia onset was reduced in lambs asphyxiated with their head in cool water (-34±2%) and warm water (-25±4%) compared with those in air (-11±5%; p<0.05). Similarly, the decrease in blood pressure was faster in lambs with water around the face compared with those in air. From 75 s after asphyxia onset, mean and end-diastolic carotid blood flow was higher in the group asphyxiated in air (25±4 mL/kg/min), compared with the groups in water (13±3 mL/kg/min, warm water; 16±2 mL/kg/min, cool water; p<0.05).
The cardiovascular response to birth asphyxia is altered by the presence and temperature of water surrounding the head. The previous understanding of the vagally mediated bradycardia associated with birth asphyxia may include components of the diving reflex.
持续性心动过缓被用作重度围产期窒息的主要指标。然而，子宫外窒息的羔羊与子宫内窒息的羔羊表现出不同的心动过缓反应。子宫内的局部环境可能会影响对窒息的初始心血管反应。我们评估了面部浸入水中对出生窒息心血管反应的影响。
对怀孕母羊（妊娠138±1天）进行麻醉，将胎儿取出并安装仪器以测量心肺血流动力学。在夹住脐带诱发窒息之前，羔羊的头部要么置于空气中（n = 5），要么置于温水（40±1°C；n = 5）或室温（21±1°C；n = 5）的水中。
与头部置于空气中的羔羊（-11±5%）相比，头部置于冷水（-34±2%）和温水中（-25±4%）的窒息羔羊心动过缓发作后的心率降低（p<0.05）。同样，面部周围有水的羔羊血压下降比置于空气中的羔羊更快。窒息发作后75秒起，置于空气中窒息组的平均和舒张末期颈动脉血流量较高（25±4 mL/kg/min），而置于水中的组（温水组为13±3 mL/kg/min；冷水组为16±2 mL/kg/min；p<0.05）。
头部周围水的存在和温度会改变对出生窒息的心血管反应。先前对与出生窒息相关的迷走神经介导的心动过缓的认识可能包括潜水反射的成分。
