Neurobehavioral stress linked to the central nervous system is associated with heart rate variability differences in preterm infants

OBJECTIVE: NeoNatal Neurobehavioral (NNNS-II) Scale measures behavioral signs of stress according to systems, including the autonomic and central nervous systems. These systems influence heart rate variability which is a biomarker for regulatory capacity. The present study aims to investigate whether patterns of autonomic dysregulation are evident in both behavioral and physiological measures. STUDY DESIGN: Heart rate variability metrics-short- and long-term fractal scaling exponents (alpha1, alpha2) and root mean square fluctuations (RMS1, RMS2)-were calculated from the heart rates of 51 preterm infants at 33 weeks postmenstrual age. The NNNS-II assessments were conducted at term-equivalent age. RESULTS: Linear regression revealed that higher total stress signs were associated with increased alpha2 (β =.366, p =.006), indicating reduced long-scale autonomic complexity. Autonomic and central nervous system-specific stress signs were significantly associated with elevated alpha2 (β = .349, p = .022). Individual items such as high-frequency tremors were also associated with increased alpha2 (β = .303, p = .018) whereas startles were not (p = .096). CONCLUSION: Neurobehavioral stress signs, particularly those associated with the central nervous system, are linked to early diminished autonomic variation in infants. These findings can help researchers and clinicians interpret the significance of neurobehavioral stress signs to autonomic tone in preterm infants.