title: Redistribution of power spectrum of heart rate variability during acute umbilical artery embolism and hypoxemia in late-gestation fetal sheep.
abstract: OBJECTIVE
  Fetal heart rate variability (HRV) is subject to a number of factors, including fetal distress. The aim of this study was to investigate the power spectral distribution of fetal heart rate variability during acute hypoxemia following umbilical artery embolism and to test the hypothesis that the relative proportion of frequency domains in total power of HRV, reflects the changes in HRV during hypoxemia more closely than the absolute values.
  
  
  METHODS
  Acute hypoxemia was induced in seven catheterized late-gestation fetal sheep by repeated injections of microspheres to cause umbilical artery embolism. The very-low, low-, middle- and high-frequency domains (0-0.025, 0.025-0.125, 0.125-0.20, and 0.20-0.50 cycles/beat, respectively) were determined by power spectral analysis.
  
  
  RESULTS
  Umbilical artery embolism induced marked fetal hypoxemia, hypercapnia and acidosis, accompanied by an increase in heart rate and a decrease in arterial blood pressure. These changes were associated with the increase in power over the entire frequency range and in the relative power in the low-frequency range (P<0.01), and with decrease in the relative power in the high-frequency range (P<0.05). Correlations were found between the relative power in the low- and high-frequency ranges and PO2 and between the relative power in these ranges and mean arterial blood pressure (P<0.05), but not PCO2 or pH.
  
  
  CONCLUSIONS
  The present study indicates that acute hypoxemia induced by umbilical artery embolism leads to the redistribution of power spectral density of fetal HRV and that the relative proportion of individual frequency domains may reflect the changes in HRV during acute hypoxemia more closely than the absolute power values.
authors.affiliation: The Obstetrics & Gynecology Hospital, Fudan University, 419 Fangxie Road, Shanghai 200011, China. xiaotianli555@hotmail.com
authors.forename: Xiaotian
authors.initials: X
authors.lastname: Li
authors.forename: Dakan
authors.initials: D
authors.lastname: Tang
authors.forename: Shufeng
authors.initials: S
authors.lastname: Zhou
authors.forename: Guangxing
authors.initials: G
authors.lastname: Zhou
authors.forename: Caiyan
authors.initials: C
authors.lastname: Wang
authors.forename: Yiliang
authors.initials: Y
authors.lastname: Zhuang
authors.forename: Guoqiang
authors.initials: G
authors.lastname: Wu
authors.forename: Linlin
authors.initials: L
authors.lastname: Shen
mesh_terms: D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure; D003201:Computers; D004617:Embolism / Q000150:complications*; D005260:Female; D005865:Gestational Age; D006340:Heart Rate, Fetal; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology*; D008863:Microspheres; D011247:Pregnancy; D012756:Sheep / Q000196:embryology*; D014469:Umbilical Arteries