OBJECTIVE: We investigated whether there are differences in autonomic cardiovascular regulation in resuscitated patients undergoing therapeutic hypothermia (TH) in relation to the clinical outcome. METHOD: Between 2005 and 2007, 18 consecutive resuscitated patients were enrolled. ECG and blood pressure data were recorded for 48 h during hypothermia and warming up to a body core temperature of 36 degrees C. Autonomic regulation was assessed by applying time, frequency, and non-linear dynamics domain methods from heart rate and blood pressure variability (HRV/BPV) analyses. RESULTS: Nine patients survived with good neurological recovery, and nine patients died during the ICU stay. In both groups, we found a decreased HRV presented by standard deviation of R-R intervals (sdNN) below 50 ms(2) at each time of measurement. Immediately after recovery to a body core temperature of 36 degrees C, a significant higher HRV was found in survivors compared to non-survivors by means of indices sdNN (40.2 +/- 19.5 vs. 10.9 +/- 4.1 ms(2), P = 0.01), R-R intervals distribution histogram [shannon] (3.7 +/- 0.6 vs. 2.2 +/- 0.4, P = 0.008), very low frequency band [VLF] (152.2 +/- 99.3 vs. 3.4 +/- 1.9, P = 0.001) and the variance of the time series of R-R intervals [Wsdvar] (1.16 +/- 0.52 vs. 0.29 +/- 0.25, P = 0.02) . A decreased spontaneous BPV was found only among survivors comparing blood pressure characteristics within stable hypothermia to the initial state before hypothermia. CONCLUSION: Resuscitated patients show a significantly reduced HRV before, during and after TH. Compared to survivors, the non-survivors show a further and significantly decrease of HRV immediately after hypothermia.