  Fetal heart rate variability (fHRV) is an important indicator of health and
disease, yet its physiological origins, neural contributions in particular, are
not well understood. We aimed to develop novel experimental and data analytical
approaches to identify fHRV measures reflecting the vagus nerve contributions
to fHRV. In near-term ovine fetuses, a comprehensive set of 46 fHRV measures
was computed from fetal pre-cordial electrocardiogram recorded during surgery
and 72 hours later without (n=24) and with intra-surgical bilateral cervical
vagotomy (n=15). The fetal heart rate did not change due to vagotomy. We
identify fHRV measures specific to the vagal modulation of fHRV: Multiscale
time irreversibility asymmetry index (AsymI), Detrended fluctuation analysis
(DFA) alpha1, Kullback-Leibler permutation entropy (KLPE) and Scale dependent
Lyapunov exponent slope (SDLE alpha). We provide a systematic delineation of
vagal contributions to fHRV across signal-analytical domains which should be
relevant for the emerging field of bioelectronic medicine and the deciphering
of the vagus code. Our findings also have clinical significance for in utero
monitoring of fetal health during surgery.
