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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\u2010like 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\u2010hydroxydopamine (6\u2010OHDA; <jats:italic>n<\/jats:italic>\u00a0=\u00a06) or sham treatment (control; <jats:italic>n<\/jats:italic>\u00a0=\u00a07), followed 4\u20135\u00a0days later by 2\u00a0min episodes of complete umbilical cord occlusion repeated every 5\u00a0min for up to 4\u00a0h, or until mean arterial blood pressure fell to &lt;20\u00a0mmHg for two successive occlusions. FHRV was decreased before occlusions in the 6\u2010OHDA group (<jats:italic>P<\/jats:italic>\u00a0&lt;\u00a00.05) and 2\u20134.5\u00a0h during recovery after occlusions (<jats:italic>P<\/jats:italic>\u00a0&lt;\u00a00.05) 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 (<jats:italic>P<\/jats:italic>\u00a0&lt;\u00a00.05), 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.<\/jats:p><\/jats:sec>","DOI":"10.1113\/jp270125","type":"journal-article","created":{"date-parts":[[2015,4,10]],"date-time":"2015-04-10T21:44:34Z","timestamp":1428702274000},"page":"1265-1277","source":"Crossref","is-referenced-by-count":52,"title":["Sympathetic neural activation does not mediate heart rate variability during repeated brief umbilical cord occlusions in near\u2010term fetal sheep"],"prefix":"10.1113","volume":"594","author":[{"given":"Christopher A.","family":"Lear","sequence":"first","affiliation":[{"name":"The Fetal Physiology and Neuroscience Group, Department of Physiology The University of Auckland  Auckland New Zealand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Robert","family":"Galinsky","sequence":"additional","affiliation":[{"name":"The Fetal Physiology and Neuroscience Group, Department of Physiology The University of Auckland  Auckland New Zealand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Guido","family":"Wassink","sequence":"additional","affiliation":[{"name":"The Fetal Physiology and Neuroscience Group, Department of Physiology The University of Auckland  Auckland New Zealand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Clinton J.","family":"Mitchell","sequence":"additional","affiliation":[{"name":"The Fetal Physiology and Neuroscience Group, Department of Physiology The University of Auckland  Auckland New Zealand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Joanne O.","family":"Davidson","sequence":"additional","affiliation":[{"name":"The Fetal Physiology and Neuroscience Group, Department of Physiology The University of Auckland  Auckland New Zealand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jennifer A.","family":"Westgate","sequence":"additional","affiliation":[{"name":"The Fetal Physiology and Neuroscience Group, Department of Physiology The University of Auckland  Auckland New Zealand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Laura","family":"Bennet","sequence":"additional","affiliation":[{"name":"The Fetal Physiology and Neuroscience Group, Department of Physiology The University of Auckland  Auckland New Zealand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alistair J.","family":"Gunn","sequence":"additional","affiliation":[{"name":"The Fetal Physiology and Neuroscience Group, Department of Physiology The University of Auckland  Auckland New Zealand"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2015,5,22]]},"reference":[{"key":"e_1_2_6_2_1","doi-asserted-by":"publisher","DOI":"10.1016\/S0165-3806(96)80010-1"},{"key":"e_1_2_6_3_1","doi-asserted-by":"publisher","DOI":"10.1152\/ajpheart.1985.249.4.H867"},{"key":"e_1_2_6_4_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1471-0528.2007.01479.x"},{"key":"e_1_2_6_5_1","doi-asserted-by":"publisher","DOI":"10.1016\/S0140-6736(01)05703-8"},{"key":"e_1_2_6_6_1","unstructured":"J. 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