Background 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.
Methods 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.
Results 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).
Conclusions 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.
- Animal Research
- Basic Science
- Fetal Medicine
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Contributors TO wrote the ethics application, participated in the study design and coordination, collected the data, reviewed the literature, wrote a first draft and submitted the manuscript. KSS and KJC collected the data and edited the manuscript. MLS and JJvV collected the data. GRP and SBH participated in the study design and coordination, data collection and edited the manuscript. All authors have read and approved the final manuscript.
Funding This research was supported by a National Institute of Health R01HD072848-01A1, NH&MRC Research Fellowships (GRP: 1026890 and SBH: 545921), a Rebecca L Cooper Medical Research Foundation Fellowship (GRP) and the Victorian Government's Operational Infrastructure Support Program.
Competing interests None declared.
Ethics approval The experimental protocol was performed in accordance with the guidelines established by the National Health and Medical Research Council of Australia and received approval of the Monash Medical Centre, Monash University Animal Ethics Committee.
Provenance and peer review Not commissioned; externally peer reviewed.