title: The cardiovascular response to birth asphyxia is altered by the surrounding environment.
abstract: 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.
authors.affiliation: The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Victoria, Australia.|Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia.
authors.forename: Tracey
authors.initials: T
authors.lastname: Ong
authors.affiliation: The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Victoria, Australia.|Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia.
authors.forename: Kristina S
authors.initials: KS
authors.lastname: Sobotka
authors.affiliation: The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Victoria, Australia.|Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia.
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Siew
authors.affiliation: The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Victoria, Australia.|Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia.
authors.forename: Kelly J
authors.initials: KJ
authors.lastname: Crossley
authors.affiliation: Division of Neonatology, Department of Pediatrics, Leiden, The Netherlands.
authors.forename: Jeroen J
authors.initials: JJ
authors.lastname: van Vonderen
authors.affiliation: The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Victoria, Australia.|Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia.
authors.forename: Graeme R
authors.initials: GR
authors.lastname: Polglase
authors.affiliation: The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Victoria, Australia.|Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia.
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Hooper
keywords: Animal Research; Basic Science; Fetal Medicine; Neonatology; Resuscitation