Comparison of Heart Rate Variability Measured by ECG in Different Signal Lengths


      The measurement of heart rate variability, HRV, provides a noninvasive measurement of the autonomic nervous system (ANS) activity. HRV can be measured with the variation of RR intervals exhibited in a sequence of ECG sample. For a short-term HRV, the measuring time is usually five minutes. However, there are still many expectations of shortening the measuring time to evaluate the ANS. In this paper we analyzed and compared three minute HRV measurement to five minute standard short-term HRV. In order to evaluate the measurement results based on three minute and five minute HRVs, four major measurements were calculated in this study. The first is the standard deviation of normal-beat to normal-beat intervals (SDNN). The second is the square root of the mean squared differences of successive difference normal-beat to normal-beat intervals (RMSSD). The third is the proportion of interval differences of successive normal-beat to normal-beat intervals greater than 50 ms (pNN50). The fourth is the ratio of low frequency energy to high frequency energy (LF/HF) based on Fourier analysis method. Results show that the HRV presented by both SDNN and LF/HF using the three-minute measuring data differs significantly from that using the five-minute measuring data. In addition, the characteristics of HRV under different heart rate conditions shows that faster heart rate will come out smaller HRV. In conclusion, the HRV analyzed based on three minutes measuring data would not be equaled to that of five minutes measuring data. At the same time, the conditions of heart rate need to be considered when heart rate variability was analyzed.