No abstract

Human neonates (average age, 36 hours) discriminated three facial expressions (happy, sad, and surprised) posed by a live model as evidenced by diminished visual fixation on each face over trials and renewed fixations to the presentation of a different face. The expressions posed by the model, unseeen by the observer, were guessed at greater than chance accuracy simply by observing the face of the neonate, whose facial movements in the brow, eyes, and mouth regions provided evidence for imitation of the facial expressions.

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The relationship between heart rate (HR) and oxygen consumption (V̇o2) has been investigated in a sample of 20 low‐risk, term neonates aged 14–48 hrs. Repeated, simultaneous measurements of HR and V̇o2 were performed on each neonate during each of three epochs ordered by increasing level of activity. A robust linear relationship was found between HR and V̇o2, with an average correlation of.90. Substantial variation was observed across individuals in the slope of the HR‐V̇o2 regression line. This variation was curvilinearly related to ponderal index (PI), with low PI neonates having the shallowest and steepest slopes. These findings suggest that HR may provide a flexible, non‐restrictive means of estimating neonatal V̇o2 but that the impact of prenatal growth history and postnatal growth performance on the estimation of V̇o2 from HR merits further investigation.

A laboratory and a field experiment used within-subject designs to test the hypothesis that nonnutritive sucking (NNS) reduces heart rate (HR) in preterm infants. Infants in Experiment A were provided a standard pacifier nipple for 30 min under strictly controlled conditions. In the field Experiment B, nursing staff provided infants with a standard pacifier during alternate intervals in a sequence of four interfeed intervals spanning 12 hr. NNS significantly reduced average HR in each experiment. Given the strongly positive relationship between HR and energy expenditure, these results suggest that NNS reduces energy expenditure in preterm infants. Such an effect, in turn, could help to explain how the opportunity to engage in NNS enhances growth in preterms.