Heart rate as an indicator of the behavioral state. Studies in the newborn infant and prospects for fetal heart rate monitoring.

Term healthy newborn infants underwent polygraphy between days 4 and 6 of life. Behavioral states were determined according to Prechtl's criteria. The neonatal heart rate was analyzed for the various behavioral states, with the use of quantitative indices for long-term and short-term irregularity. The applied indices were, respectively, the long-term irregularity index (LTI index) and the interval difference index (ID index). During state 1 the R-R interval length was longer (p less than 0.01), the LTI index lower (p less than 0.01), and the ID index higher (p less then 0.02) than in the immediately preceding or following state 2. For nonconsecutive states 1 and 2 a maximum separation was obtained with the discriminant function 0.0159 RR - 0.065 LTI + 0.062 ID - 7.49. This discriminant function gave a total percentage of correct classification of states 1 and 2 epochs of 93%. The data are discussed with respect to the presence of cycling sleep states in the newborn infant as well as in the fetus. Prospects for fetal antepartum heart rate monitoring are considered.