Exposure to chronic hypoxia in late gestation fetal sheep impaired gestational age-related increases in overall FHRV and suppressed sympathetic nervous system control of FHRV (P<0.001).
Does chronic hypoxia alter the autonomic control of fetal heart rate variability in late gestation fetal sheep?
Chronic hypoxia impairs the normal gestational increase in fetal heart rate variability in sheep, predominantly through suppression of sympathetic control, providing a physiological basis for FHRV as a biomarker of fetal compromise.
p-value: p=<0.001
KEY POINTS: Fetal heart rate variability (FHRV) has long been recognised as a powerful predictor of fetal wellbeing, and a decrease in FHRV is associated with fetal compromise. However, the mechanisms by which FHRV is reduced in the chronically hypoxic fetus have yet to be established. The sympathetic and parasympathetic influences on heart rate mature at different rates throughout fetal life, and can be assessed by time domain and power spectral analysis of FHRV. In this study of chronically instrumented fetal sheep in late gestation, we analysed FHRV daily over a 16 day period towards term, and compared changes between fetuses of control and chronically hypoxic pregnancy. We show that FHRV in sheep is reduced by chronic hypoxia, predominantly due to dysregulation of the sympathetic control of the fetal heart rate. This presents a potential mechanism by which a reduction in indices of FHRV predicts fetuses at increased risk of neonatal morbidity and mortality in humans. Reduction in overall FHRV may therefore provide a biomarker that autonomic dysregulation of fetal heart rate control has taken place in a fetus where uteroplacental dysfunction is suspected. ABSTRACT: 10-12 mmHg), and a customised wireless data acquisition system to record beat-to-beat variation in the fetal heart rate. We determined in vivo longitudinal changes in overall FHRV and the sympathetic and parasympathetic contribution to FHRV in hypoxic (n = 6) and normoxic (n = 6) ovine fetuses with advancing gestational age. Normoxic fetuses show gestational age-related increases in overall indices of FHRV, and in the sympathetic nervous system contribution to FHRV (P < 0.001). Conversely, gestational age-related increases in overall FHRV were impaired by exposure to chronic hypoxia, and there was evidence of suppression of the sympathetic nervous system control of FHRV after 72 h of exposure to hypoxia (P < 0.001). This demonstrates that exposure to late gestation isolated chronic fetal hypoxia has the potential to alter the development of the autonomic nervous system control of FHRV in sheep. This presents a potential mechanism by which a reduction in indices of FHRV in human fetuses affected by uteroplacental dysfunction can predict fetuses at increased risk.
Shaw et al. (2018) studied Chronic fetal hypoxia (n=12). Chronic hypoxia vs. Normoxia was evaluated on Overall fetal heart rate variability (FHRV) and sympathetic/parasympathetic contribution (p=<0.001). Exposure to chronic hypoxia in late gestation fetal sheep impaired gestational age-related increases in overall FHRV and suppressed sympathetic nervous system control of FHRV (P<0.001).