Electrical Grounding Improves Vagal Tone in Preterm Infants

Abstract

Background: Low vagal tone (VT) is a marker of vulnerability to stress and the risk of developing necrotizing enterocolitis in preterm infants. Electric fields produced by equipment in the neonatal intensive care unit (NICU) induce an electric potential measurable on the skin in reference to ground. An electrical connection to ground reduces the skin potential and improves VT in adults.

Objectives: We aimed to measure the electric field strengths in the NICU environment and to determine if connecting an infant to electrical ground would reduce the skin potential and improve VT. We also wished to determine if the skin potential correlated with VT.

Methods: Environmental magnetic flux density (MFD) was measured in and around incubators. Electrical grounding (EG) was achieved with a patch electrode and wire that extended to a ground outlet. We measured the skin potential in 26 infants and heart rate variability in 20 infants before, during, and after grounding. VT was represented by the high-frequency power of heart rate variability.

Results: The background MFD in the NICU was below 0.5 mG, but it ranged between 1.5 and 12.7 mG in the closed incubator. A 60-Hz oscillating potential was recorded on the skin of all infants. With EG, the skin voltage dropped by about 95%. Pre-grounding VT was inversely correlated with the skin potential. VT increased by 67% with EG. After grounding, the VT fell to the pre-grounding level.

Conclusion: The electrical environment affects autonomic balance. EG improves VT and may improve resilience to stress and lower the risk of neonatal morbidity in preterm infants.

Keywords: Electrical grounding; Electromagnetic fields; Heart rate variability; Vagal tone.

© 2017 S. Karger AG, Basel.

Figures

Fig. 1

The columns represent the magnetic flux density (MFD) within the standard incubator measured at the mattress level. The MFD ranged between 1.5 and 12.7 mG. The field strength was highest above the power supply and near the control panel.

Fig. 2

Recording of skin surface potential. A 1-s interval is shown. The field alternates at 60 Hz. At the onset of electrical grounding (arrow), the voltage diminished immediately. The mean decrease in voltage ± SE was 95.6 ± 1.1% (p < 0.001, paired sample t test).