A number of developmental disorders in children, including learning disabilities, can be traced to deficits in attention and abnormalities in autonomic nervous system (ANS) functioning. A vagally-mediated decrease in heart rate is used as a marker of attention in infants, and an association between prestimulus respiratory sinus arrhythmia (RSA) and the magnitude of the heart rate deceleration has been demonstrated. Evaluation of ANS functioning and information processing capabilities are particularly well- suited for assessing central nervous system (CNS) status in utero: the ANS can be examined in human fetuses noninvasively using spectral decomposition techniques, and human fetuses are capable of displaying a heart rate deceleratory response to certain acoustic stimuli. After identifying acoustic parameters which consistently elicit a heart rate deceleration in normal human term fetuses, we will examine the relationship between prestimulus RSA and the magnitude of the cardiac deceleratory response and determine if there is a decrease in respiratory frequency and heart rate variability (HRV) concomitant with the heart rate deceleration. Furthermore, we will determine if fetuses categorized as sympathetic-dominant exhibit a different type of cardiac response to low- intensity acoustic stimuli than fetuses categorized as parasympathetic- dominant and whether these characteristics are stable over time. Special emphasis will be placed on identifying parameters which are capable of distinguishing growth-restricted fetuses and fetuses with CNS structural anomalies from normal fetuses. An important aspect of the proposed study plan is that subjects examined as fetuses will be examined again as neonates and will be followed prospectively to two years of age. The fetal electrocardiogram will be captured noninvasively using standard cardiac electrodes positioned on the mother's abdomen. Adaptive signal processing methodology will be used to extract fetal R-waves from the raw data. Sympathetic-parasympathetic balance will be evaluated by applying spectral decomposition techniques to the analysis of fetal and neonatal HRV data. The heart rate response to low-intensity acoustic stimuli will be related to ANS functioning in both fetuses and neonates. We believe that differences in intrinsic ANS activity and cardiac responsivity may ultimately help to identify the fetus at-risk for neurobehavioral abnormalities and hence facilitate the implementation of appropriate intervention protocols early in the course of development.
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| Groome, L J; Mooney, D M; Holland, S B et al. (1997) The heart rate deceleratory response in low-risk human fetuses: effect of stimulus intensity on response topography. Dev Psychobiol 30:103-13 |
