The role of autonomic nervous system function in hypothermia-mediated sepsis protection

Abstract Objective The objective of this study is to determine whether hypothermia will lessen decreases in heart rate variability and improve outcome in a rat model of sepsis. Methods Thirty-six male Sprague-Dawley rats were randomized into 3 groups: control, low sepsis, and high sepsis groups. These groups were each subdivided into a normothermia (37°C) (n = 6) and a hypothermia group (34°C) (n = 6). Cyclophosphamide (100 mg/kg) was administered 5 days before Staphylococcus aureus injection to produce conditions in which sepsis could be induced reliably. Hypothermic rats received temperature reduction for 1 hour post injection. Electrocardiogram was recorded before, after, and 1 day after staphylococcal injection, and the low frequency, high frequency (HF), and LF/HF ratio measurements of heart rate variability and the frequencies of arrhythmia were recorded. The effects of time, sepsis severity, and hypothermia on these variables were analyzed using a multivariate generalized estimation equation mode. Results Four deaths occurred in the normothermic group, and none, in the hypothermic group. Sepsis of both low and high severity increased low frequency and HF 1 day after sepsis induction. Hypothermia significantly decreased HF in low, but not high sepsis severity. Conclusions Hypothermia decreased mortality in septic rats. The influence of hypothermia on HF depended on the severity of the sepsis.