Newborn infants demonstrate individual differences in cardiac reactivity to a standard stimulus, which can be quantified using specific time and magnitude parameters.
Methodologic techniques described in a previous report were explored in a group of 16 newborn infants. Cardiac-rate responses to a standard stimulus provided the data which were analyzed for purposes of differentiation of subjects. Estimates of clearly defined physiologic parameters which were extracted from each response trial can be categorized in two groups: time and magnitude. The former parameters appeared unrelated to prestimulus heart rate level and were analyzed by means of more simple parametric techniques. Individual infants were differentiated in this manner both in terms of the mean and the variability of the time parameters. The finding of significant correlations between the magnitude parameters and the prestimulus heart rate suggested the use of a regression model for statistical analysis. A proposed measure of maximal reactive capacity was derived for each infant and each parameter with respective error estimates. These too differentiated subjects. The implications and limitations of these data, as well as other response measures for the comparison of individuals, were discussed.
Lipton et al. (Wed,) studied this question.