Heart rate variability parameters during endotoxemia. Left panel: ratio between low frequency and high frequency power (LF/HF). Right panel: high frequency power in normalized units (HFnu). Data are expressed as mea SEM of 10 subjects per group. LH/HF was log-transformed to attain normal distribution. Gray box indicates period in which the (sham) stimulation took place. P-values indicate differences between groups over time calculated using repeated measures two-way analysis of variance (ANOVA, interaction term). AU: arbitrary units.