title: Ontogeny and control of the heart rate power spectrum in the last third of gestation in fetal sheep.
abstract: Power spectral analysis of fetal heart rate variability has been proposed to provide a non-invasive estimate of autonomic balance. However, there are few systematic data before birth. We therefore examined developmental changes in the frequency power spectrum at very low (0-0.04 Hz), low (0.04-0.15 Hz) and high frequencies (0.15-0.4 Hz), as well as the ratio of low- to high-frequency power (LF/HF), in chronically catheterized, healthy fetal sheep at 0.6 (n = 8), 0.7 (n = 7) and 0.8 gestational age (ga; n = 11). In a second study, 0.8 ga fetuses received either atropine (4.8 mg bolus, then 4.8 mg h(-1) for 30 min, n = 6) or 6-hydroxydopamine (20 mg ml(-1) at 2.5 ml h(-1) for 3 h; n = 9). Data were analysed by sleep state, defined by low-voltage-high-frequency (LV) or high-voltage-low-frequency (HV) EEG. Total spectral power increased with gestational age (P < 0.05), while LF/HF decreased from 0.6 to 0.7 ga. At 0.8 ga, heart rate and LF/HF were significantly higher during HV than LV sleep (P < 0.05). Consistent with this, although total spectral power was not significantly greater during HV sleep, there was a significant interaction between sleep state and frequency band (P = 0.02). Both atropine (P = 0.05) and 6-hydroxydopamine (P < 0.05) were associated with an overall reduction in spectral power but no significant effect on the LF/HF ratio. This study does not support substantial, consistent differences between the frequencies of sympathetic and parasympathetic activity in late-gestation fetal sheep.
authors.affiliation: A. J. Gunn: Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Private Bag 92019, Auckland, New Zealand. aj.gunn@auckland.ac.nz.
authors.forename: Miriam E
authors.initials: ME
authors.lastname: Koome
authors.forename: Laura
authors.initials: L
authors.lastname: Bennet
authors.forename: Lindsea C
authors.initials: LC
authors.lastname: Booth
authors.forename: Joanne O
authors.initials: JO
authors.lastname: Davidson
authors.forename: Guido
authors.initials: G
authors.lastname: Wassink
authors.forename: Alistair Jan
authors.initials: AJ
authors.lastname: Gunn
mesh_terms: D000818:Animals; D005260:Female; D005333:Fetus / Q000502:physiology*; D005865:Gestational Age; D006339:Heart Rate / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000502:physiology; D011247:Pregnancy; D012756:Sheep / Q000502:physiology*; D012890:Sleep / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology