Figure 2

Time course analysis of heart rate and heart rate variability following laparotomy. Changes (delta) in heart rate [HR, beats per minute (bpm)], interbeat interval [IBI, milliseconds (ms)], and standard deviation of interbeat interval [SDNN, milliseconds (ms)] relative to baseline (i.e., normal values taken the day before the experiment) are plotted over time. Symbols indicate 12-hour means (bars indicate ± SEM). Corresponding control experiments in which animals received anesthesia and injections only are depicted as black horizontal lines with grey columns representing ± SEM. Asterisks indicate statistical significance (n = 8, paired Student's t test with Bonferroni correction) at P ≤ 0.008. Note increased heart rate values with decreased heart rate variability parameters [IBI, SDNN] during the first light phase (12–24 h) in operated animals without pain treatment.