Vagal Dysregulation in the First Week of Life is Associated with Markedly Increased Pro-Inflammatory Cytokines and Late Onset Sepsis or Necrotizing Enterocolitis in Preterm Neonates

Necrotizing enterocolitis (NEC) is the leading cause of death in premature neonates due to gastrointestinal disease. Known risk factors include low birth weight, formula feeding, and chorioamnionitis. NEC is most often characterized by an insidious onset of symptoms such as feeding intolerance and abdominal distension, followed by a rapid progression to fulminant sepsis and bowel necrosis. There are currently no non-invasive ways for clinicians to predict NEC before its onset. Heart rate variability (HRV) is a non-invasive way to measure changes in vagal tone, and the high-frequency (HF) component specifically measures parasympathetic activity. Our laboratory has shown that HF-HRV is a useful factor to predict NEC in neonates before the onset of clinical signs. We therefore hypothesized that decreased HF-HRV would be present in neonates at risk for NEC before the onset of symptoms, possibly due to a diminution in the vagal cholinergic anti-inflammatory pathway. As a result of changes to this pathway, pro-inflammatory cytokine levels would be elevated before the onset of symptoms, in conjunction with the diminished vagal tone assessed by HF-HRV.

We prospectively studied 126 preterm neonates (30.9±2.1wks; 1570±463g at birth); exclusion criteria included congenital abnormalities, CNS lesions, or other conditions known to affect autonomic nervous system functioning. Spectral analysis of postprandial resting vagal tone derived from the analog ECG signal was measured on day 5-8 of life, and weekly thereafter. Whole blood collected at day 5-8 and day 21 of life was used to quantify levels of TNF-α, IL-6, IL-8, IFN-γ, IL-1β, and IL-10 using the Meso Scale Discovery Multi-Spot Assay System. Additionally, clinical outcomes were followed throughout hospitalization. Two of 126 (1.6%) neonates developed Stage II or greater NEC, diagnosed via the Modified Bell's Staging Criteria, and 6 of 126 (4.8%) neonates developed late onset sepsis or clinical infection. HF-HRV measures taken at 5-8 days of life were significantly lowered in neonates who later developed NEC or clinical infection versus healthy neonates. Complete cytokine data were available on 84 neonates. TNF-α, IL-6, and IL-8 were significantly higher in neonates at 21 days of life who later developed NEC or clinical infection, as compared to healthy neonates.

Overall, these data show an inverse correlation between HF-HRV measures and levels of pro-inflammatory cytokines TNF-α, IL-6, and IL-8 in neonates who later developed NEC or clinical infection. These data support indirectly the hypothesis that there is a disruption in the vagal cholinergic anti-inflammatory pathway, and confirms HF-HRV as a promising non-invasive way to measure diminished vagal tone associated with NEC or sepsis before the clinical presentation of NEC. Funded by NIH: DK09935 (RAT, KKD).