Heart rate variability characteristics required for simulation of interval sequences

Fifty sequences of PhysioNet R-to-R interval data, covering periods of between 20 and 24 hours, were classified into real or simulated groups. The RR interval characteristics were investigated in both the time domain and frequency domain. Eleven characteristics were analysed, and the range of measurements for each was studied for outliers from the main distribution. In the time domain, a restricted pattern of RR interval distributions classified 4 sequences as abnormal, and a reduced RR variability produced 18 classifications, with an overlap of 8, giving a total of 14/50 as abnormal. In the frequency domain, abnormally restricted very low frequency characteristics produced 26 classifications as abnormal with 10 overlaps giving a total of 16. The low frequency to high frequency ratio classified 4 as abnormal, but three of these were already detected by abnormal low frequency characteristics, giving a total of 17 classified in the frequency domain. Of the 17 classified in the frequency domain and of the 14 in the time domain there was an overlap of 9, resulting in 22 abnormal classifications, and suggesting that these were simulated. When PhysioNet assessed this classification a correct grouping of 100% was achieved on a single entry (reference 20020426.082234).