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This Article Full Text Full Text (PDF) All Versions of this Article: 293/3/R1287    most recent 00373.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Wibbens, B. Articles by Gunn, A. J. Search for Related Content PubMed PubMed Citation Articles by Wibbens, B. Articles by Gunn, A. J.

DEVELOPMENTAL PHYSIOLOGY AND PREGNANCY

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

¹Departments of Physiology and Obstetrics and Gynecology, Auckland University, Auckland, New Zealand; ²Department of Obstetrics and Gynecology, Academic Medical Hospital, Groningen, The Netherlands; and ³Department of Obstetrics and Gynecology, Isala Clinics, Zwolle, The Netherlands

Submitted 27 May 2007 ; accepted in final form 19 July 2007

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_O2 > 17 mmHg (n = 9) or hypoxic Pa_O2 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) µg/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.

asphyxia; fetal electrocardiogram monitoring; ST segment