Effect of Temperature on Heart Rate Variability in Neonatal ICU Patients With Hypoxic-Ischemic Encephalopathy

Abstract

Objective To determine whether measures of heart rate variability (HRV) are related to changes in temperature during rewarming after therapeutic hypothermia (TH) for hypoxic ischemic encephalopathy (HIE). Design Prospective observational study. Setting Level 4 neonatal intensive care unit in a free-standing academic children's hospital. Patients Forty-four infants with moderate to severe HIE treated with TH. Interventions Continuous EKG data from 2 hours prior to rewarming through 2 hours after completion of rewarming (up to 10 hours) were analyzed. Measurements and Main Results Median beat-to-beat interval (RRi) and measures of HRV were quantified including RRi standard deviation (SD), low (LF) and high (HF) frequency relative spectral power, detrended fluctuation analysis short- and long- α exponents (αS, αL) and root mean square short- and long- time scales (RMSS, RMSL). The relationships between HRV measures and esophageal/axillary temperatures were evaluated. HRV measures LF, αS, RMSS, and RMSL were negatively associated, while αL was positively associated, with temperature (P<0.01). These findings signify an overall decrease in HRV as temperature increased towards normothermia. Conclusions Measures of HRV are temperature dependent in the range of TH to normothermia. Core body temperature needs to be considered when evaluating HRV metrics as potential physiological biomarkers of illness severity in HIE infants undergoing TH.

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“…), temperature itself causes changes in HRV (Massaro et al. ), and HF power was increased the most in infants with moderate EEG findings of HIE as compared to those with mild EEG findings of HIE (Goulding et al. ).…”

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“…The main difference between this study and the previous study from the same group [21] was treatment with therapeutic hypothermia in the later. However, other studies have found no effect of temperature on SDNN in neonates with HIE but have reported an increase in HF in absolute power during rewarming and a negative association between LF in relative power and temperature [26,44].…”