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Infants Born Preterm Exhibit Different Patterns of Center-of-Pressure Movement Than Infants Born at Full Term

S.C. Dusing, PT, PhD, is Assistant Professor, Department of Physical Therapy, Virginia Commonwealth University, PO Box 980224, Richmond, VA 23298 (USA).
A. Kyvelidou, MS, is Graduate Research Assistant, Nebraska Biomechanics Core Facility, University of Nebraska Medical Center and University of Nebraska at Omaha, Omaha, Nebraska.
V.S. Mercer, PT, PhD, is Associate Professor, Division of Physical Therapy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
N. Stergiou, PhD, is Isaacson Professor and Director, Nebraska Biomechanics Core Facility, College of Education and College of Public Health, University of Nebraska Medical Center and University of Nebraska at Omaha.

scdusing{at}vcu.edu

Background: Infants born preterm are at risk for developmental impairments related to postural control.

Objective: The purpose of this study was to determine whether infants born preterm and infants born at full term differed in postural control at 1 to 3 weeks after term age.

Design: This study included 17 infants born preterm (mean gestational age=31.9 weeks, range=25.0–34.6) and 15 infants born at full term (mean gestational age=38.9 weeks, range=37.3–40.6) without diagnosed neurological or genetic conditions.

Measurement: Center-of-pressure (COP) data were recorded at 5 Hz while each infant was positioned supine on a pressure-sensitive mat in an alert behavioral state. Root mean square (RMS) displacement and approximate entropy (ApEn) were used to describe the COP movement variability in the time series. Differences between groups were identified using independent t tests.

Results: The COP time series were found to be deterministic, suggesting order in the time series. Infants born preterm exhibited significantly larger RMS values in the caudal-cephalic direction than infants born at full term (1.11 and 0.83 cm, respectively; t=–2.6, df=30, P=.01). However, infants born at full term had significantly larger ApEn values in the caudal-cephalic direction (1.19 and 1.11, respectively; t=2.4, df=30, P=.02). The 2 groups did not differ in RMS or ApEn values in the medial-lateral direction or the resultant.

Conclusions: Infants born at full term exhibited COP displacements in the caudal-cephalic direction that were smaller in amplitude, but may be considered more complex or less predictable, than those of infants born preterm. One explanation is that infants born preterm exhibited more stereotypic patterns of movement, resulting in large, but repetitive, COP excursions. A combination of linear and nonlinear measures may provide insight into the control of posture of young infants.

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