Ontogenetic development of neural control of the heart rate in the human fetus quantitatively assessed using a probability matrix.

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For the past 3 years, we quantitatively analyzed, using a probability matrix, the age-related fetal heart rate changes in the fetuses with hydrocephalus and anencephalous as well as the normal fetuses.1. Analyzed was the age-related characteristics of FHR variation in normal fetuses from 20 to 41 weeks' gestation, using the "congruence rate" between the standard matrix constructed from the original whole data in each 2 consecutive gestational age and the matrix produced from a small sample of FIIR data randomly selected from the original data set, as a parameter. The minimum number of FHR beats necessary to get a "congruence rate" of 90% for the standard probability matrix was 2700 beats at 27-28 weeks' gestation, gradually increasing up to about 6000 beats at 34-35 weeks' gestation. Two statistically significant critical points were found to be at 28-29 weeks' and at 34-35 weeks' gestation. These findings indicate that there were 3 different characteristics of FHR variation pertaining … More to the mechanism. of PIIR control throughout the gestational periods studied.2. Refering to the standard probability matrix for the corresponding gestational week, the age-related differences in fetal heart rate change in anencephalic or hydrocephalic fetuses was evaluated, using the 'incongruence rate" as a parameter, representing the difference between the standard matrix and the subjected matrix. In hydrocephalic fetuses, the -incongruence rate- remained within the normal range, between 11.8 and 30.6% at 31-39 weeks' gestation. On the contrary, in anencephalic fetuses, the "incongruence rate" increased, with advance in gestation, from 15.9-40.6% at 24 weeks' gestation to 36.5-45.3% at 34 weeks' gestation. and the values were beyond the normal range from 31 weeks' gestation onwards. Combining these results with autopsy findings, these suggest that the central nervous system, cephalate to the medulla, begins to play a substantial role in the control of fetal heart rate changes, at least, from 31 weeks' gestation onwards. Less