title: Preexisting hypoxia is associated with a delayed but more sustained rise in T/QRS ratio during prolonged umbilical cord occlusion in near-term fetal sheep.
abstract: There is limited information about whether preexisting fetal hypoxia alters hemodynamic responses and changes in T/QRS ratio and ST waveform shape during subsequent severe asphyxia. Chronically instrumented near-term sheep fetuses (124 +/- 1 days) were identified as either normoxic Pa(O(2)) > 17 mmHg (n = 9) or hypoxic Pa(O(2)) < or = 17 mmHg (n = 5); then they received complete occlusion of the umbilical cord for 15 min. Umbilical cord occlusion led to sustained bradycardia, severe acidosis, and transient hypertension followed by profound hypotension in both groups. Preexisting hypoxia did not affect changes in mean arterial blood pressure but was associated with a more rapid initial fall in femoral blood flow and vascular conductance and with transiently higher fetal heart rate at 2 min and from 9 to 11 min of occlusion compared with previously normoxic fetuses. Occlusion was associated with a significant but transient rise in T/QRS ratio; preexisting hypoxia was associated with a significant delay in this rise (maxima 3.7 +/- 0.4 vs. 6.2 +/- 0.5 min), but a slower rate of fall. There was a similar elevation in troponin-T levels 6 h after occlusion in the two groups [median (range) 0.43 (0.08, 1.32) vs. 0.55 (0.16, 2.32) microg/l, not significant]. In conclusion, mild preexisting hypoxia in normally grown singleton fetal sheep is associated with more rapid centralization of circulation after umbilical cord occlusion and delayed elevation of the ST waveform and slower fall, suggesting that chronic hypoxia alters myocardial dynamics during asphyxia.
authors.affiliation: Department of Physiology, The University of Auckland, Auckland, New Zealand.
authors.forename: Bert
authors.initials: B
authors.lastname: Wibbens
authors.forename: Laura
authors.initials: L
authors.lastname: Bennet
authors.forename: Jenny A
authors.initials: JA
authors.lastname: Westgate
authors.forename: Harmen H
authors.initials: HH
authors.lastname: De Haan
authors.forename: Guido
authors.initials: G
authors.lastname: Wassink
authors.forename: Alistair J
authors.initials: AJ
authors.lastname: Gunn
mesh_terms: D000653:Amniotic Fluid / Q000502:physiology; D000818:Animals; D001784:Blood Gas Analysis; D001786:Blood Glucose / Q000378:metabolism; D001794:Blood Pressure / Q000502:physiology; D002339:Carotid Arteries / Q000502:physiology; D003627:Data Interpretation, Statistical; D004562:Electrocardiography; D005260:Female; D005263:Femoral Artery / Q000502:physiology; D005311:Fetal Hypoxia / Q000503:physiopathology*; D006340:Heart Rate, Fetal / Q000502:physiology*; D006973:Hypertension / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology; D019344:Lactic Acid / Q000097:blood; D011247:Pregnancy; D012039:Regional Blood Flow / Q000502:physiology; D012756:Sheep; D020107:Troponin T / Q000097:blood; D014470:Umbilical Cord / Q000502:physiology*
chemical_list: D001786:Blood Glucose; D020107:Troponin T; D019344:Lactic Acid