Contribution of the fetal baroreceptor reflex to the low frequency component of fetal heart rate fluctuations

Objective: The objective of this study was to examine whether the fetal baroreceptor reflex contributed to the low frequency component (LF: 0.025-0.125 cycles/beat) of fetal heart rate fluctuations. Methods: Sheep fetuses in late gestation with normoxemia were used. The baroreceptor function was expressed as the baroreceptor reflex sensitivity (BRS) based on the change of the R-R interval in response to the elevation of blood pressure by noradrenaline (Nor-Ad). A frequency analysis was conducted by the autoregression method on heart rate fluctuations and blood pressure fluctuations in 300 stable heart beats immediately before the Nor-Ad test. The gain and the coherence from blood pressure LF to heart rate LF were calculated. The correlations between the BRS and the power values of heart rate LF, blood pressure LF, and the gain or the coherence were examined. Results: The BRS and the gain showed a positive correlation (p < 0.01). There was a negative correlation between the heart rate LF and the BRS, and between the blood pressure LF and the BRS (p < 0.01, p < 0.005). Conclusions: This study showed that fetal BRS was involved in the change of LF in fetal heart rate fluctuation. Baroreceptor function should be considered when examining the change of LF domain in fetal heart beat fluctuation.