Chemical sympathectomy with 6-OHDA did not significantly affect the increase in fetal heart rate variability between repeated brief umbilical cord occlusions or the transient increase in T/QRS ratio.
Does chemical sympathectomy alter fetal heart rate variability and T/QRS ratio during repeated brief umbilical cord occlusions in near-term fetal sheep?
Sympathetic nervous system activity does not mediate the increase in fetal heart rate variability or transient T/QRS ratio elevation during repeated brief umbilical cord occlusions in near-term fetal sheep.
Changes in fetal heart rate variability (FHRV) and ST segment elevation (measured as the T/QRS ratio) are used to evaluate fetal adaptation to labour. The sympathetic nervous system (SNS) is an important contributor to FHRV under healthy normoxic conditions, and is critical for rapid support of blood pressure during brief labour-like asphyxia. However, although it has been assumed that SNS activity contributes to FHRV during labour; this has never been tested, and it is unclear whether the SNS contributes to the rapid increase in T/QRS ratio during brief asphyxia. Thirteen chronically instrumented fetal sheep at 0.85 of gestation received either chemical sympathectomy with 6-hydroxydopamine (6-OHDA; n = 6) or sham treatment (control; n = 7), followed 4-5 days later by 2 min episodes of complete umbilical cord occlusion repeated every 5 min for up to 4 h, or until mean arterial blood pressure fell to <20 mmHg for two successive occlusions. FHRV was decreased before occlusions in the 6-OHDA group (P < 0.05) and 2-4.5 h during recovery after occlusions (P < 0.05) compared to the control group. During each occlusion there was a rapid increase in T/QRS ratio. Between successive occlusions the T/QRS ratio rapidly returned to baseline, and FHRV increased above baseline in both groups (P < 0.05), with no significant effect of sympathectomy on FHRV or T/QRS ratio. In conclusion, these data show that SNS activity does not mediate the increase in FHRV between repeated episodes of brief umbilical cord occlusion or the transient increase in T/QRS ratio during occlusions.
Lear et al. (2015) studied Fetal adaptation to labour / brief umbilical cord occlusions (n=13). Chemical sympathectomy with 6-hydroxydopamine (6-OHDA) vs. Sham treatment (control) was evaluated on Fetal heart rate variability (FHRV) and T/QRS ratio. Chemical sympathectomy with 6-OHDA did not significantly affect the increase in fetal heart rate variability between repeated brief umbilical cord occlusions or the transient increase in T/QRS ratio.